Pipes, Pipe Fittings, and Piping Details
Pipes are available in a variety of materials, sizes, and weights. The type selected for a particular installation will depend on a number of factors, including government codes and standards, specifications, system requirements, availability of materials, and cost. Some of these factors, such as codes and standards, will have priorities over others, but all should be given equal consideration before deciding which pipe to use. The purpose of this chapter is to offer some guidance for making these decisions.
The materials used in the manufacture of piping and tubing for steam and hydronic heating systems include the following:
• Wrought iron
• Wrought steel
• Galvanized steel
• Copper, brass, and bronze Plastic
Synthetic rubber Composites
Steel piping leads in popularity and is available in the form of either wrought steel or galvanized steel. Wrought-iron and cast-iron pipe are also used, but less frequently because of their higher cost. Copper and brass are employed in the manufacture of both pipes and tubes and find their greatest application in radiant panel heating, air-conditioning, and refrigeration systems. Other metals (for example, aluminum, bronze, and alloy metals) have also been used in the manufacture of this pipe, but with limited application due to cost, lack of availability, and other factors. In addition to steel and copper tubing, modern hydronic heating systems also commonly use plastic tubing (cross-linked polyethylene or polybutylene), synthetic rubber hose, and composite tubing.
Note
The terms pipe or piping and tube or tubing are sometimes used interchangeably, especially when referring to the piping/tubing systems of hydronic radiant panel heating systems. See Copper and Brass Piping and Tubing in this chapter.
This chapter concentrates on a description of iron, steel, copper, and brass pipes; the various types of nonmetal tubing; the pipe fittings used with them; and the methods employed in installing them.
Wrought-iron pipe enjoyed widespread use in steam heating systems prior to World War II and was still being used, although on a much smaller scale, until 1968 when its production was discontinued in the United States.
Wrought-iron pipe has been shown to have an extremely long service life. Piping systems installed 50 to 80 years ago are still operating without any signs of deterioration. This is due not only to the internal grain structure of wrought-iron pipe, but also to its high resistance to corrosion.
Note
Some ferrous metals, such as black iron (ordinary steel), are subject to corrosion if oxygen is allowed to enter the pipes. Certain types of cast-iron pipe fittings, as well as some valves and fittings, are also subject to corrosion if oxygen is present. The corrosion is irreversible.
Wrought-iron pipe differs very little in appearance from wrought — steel pipe. Indeed, were it not for special markings, the casual observer would not be able to distinguish between the two. Some wrought-iron pipe is stamped genuine wrought iron ’’on each length. More frequently, the distinguishing mark is a spiral line marked into each length of pipe. The spiral identification line may be painted onto the surface in some bright color (usually red) or knurled into the metal.
The pipe used in heating installations is manufactured for different pressures and is available in various rated sizes (also referred to as the nominal inside diameter). The three grades of wrought-iron pipe are as follows:
Standard
Extra strong (or heavy)
Double extra strong (or very heavy)
SIZE |
STANDARD |
EXTRA STRONG |
DOUBLE EXTRA STRONG |
12 |
O |
O |
O |
34 1 |
O O |
O P |
O O |
Figure 8-1 Three sizes of standard, extra-strong, and double — extra-strong wrought pipe.
The pipe sections shown in Figure 8-1 are approximately half their actual size. Figure 8-2 illustrates their actual sizes, showing proportions of the three grades of wrought pipes.
The diameters given for pipes are far from the actual diameters, especially in the small sizes. Thus, a pipe known as Vi inch (rated size) has an outside diameter of 0.54 inch and an inside diameter of 0.364 inch. Dimensions for standard, extra-strong, and double — extra-strong pipe are given in Tables 8-1, 8-2, and 8-3.
Wrought-iron pipes are adapted to higher pressures by making the walls thicker, but without changing the outside diameters. It is the inside diameter that is reduced.
|
358 |
Nominal Weight per Foot Threaded and |
Nominal |
Diameter Nominal
Vs |
0.405 |
0.269 |
0.068 |
0.245 |
Y4 |
0.540 |
0.364 |
0.088 |
0.425 |
Vs |
0.675 |
0.493 |
0.091 |
0.568 |
V2 |
0.840 |
0.622 |
0.109 |
0.852 |
3/4 |
1.050 |
0.824 |
0.113 |
1.134 |
1 |
1.315 |
1.049 |
0.133 |
1.684 |
1V4 |
1.660 |
1.380 |
0.140 |
2.281 |
1V2 |
1.900 |
1.610 |
0.145 |
2.731 |
2 |
2.375 |
2.067 |
0.154 |
3.678 |
2Vi |
2.875 |
2.469 |
0.203 |
5.819 |
3 |
3.500 |
3.068 |
0.216 |
7.616 |
3V2 |
4.000 |
3.548 |
0.226 |
9.202 |
4 |
4.500 |
4.026 |
0.237 |
10.889 |
5 |
5.563 |
5.047 |
0.258 |
14.810 |
6 |
6.625 |
6.065 |
0.280 |
19.185 |
Size External Internal |
(in) (in) (in) |
Thickness Coupled (in) (lbs) |
Transverse Area
|
Length of Pipe per Square Foot
|
Length of Pipe
Containing
I Cubic Number of
Foot Threads
(ft) per Inch
2533.775 |
27 |
1383.789 |
18 |
754.360 |
18 |
473.906 |
14 |
270.034 |
14 |
166.618 |
HVi |
96.275 |
IIV2 |
70.733 |
IIV2 |
42.913 |
IIV2 |
30.077 |
8 |
19.479 |
8 |
14.565 |
8 |
11.312 |
8 |
7.198 |
8 |
4.984 |
8 |
8 |
8.625 |
8.071 |
0.277 |
25.000 |
8 |
8.625 |
7.981 |
0.322 |
28.809 |
10 |
10.750 |
10.192 |
0.279 |
32.000 |
10 |
10.750 |
10.136 |
0.307 |
35.000 |
10 |
10.750 |
10.020 |
0.365 |
41.132 |
12 |
12.750 |
12.090 |
0.330 |
45.000 |
12 |
12.750 |
12.000 |
0.375 |
50.706 |
14 |
15.000 |
14.250 |
0.375 |
60.375 |
17 |
17.000 |
16.214 |
0.393 |
72.602 |
18 |
18.000 |
17.182 |
0.409 |
80.482 |
20 |
20.000 |
19.182 |
0.409 |
89.617 |
359 |
58.426 |
51.161 |
0.442 |
0.473 |
2.815 |
8 |
58.426 |
50.027 |
0.442 |
0.478 |
2.878 |
8 |
90.763 |
81.585 |
0.355 |
0.374 |
1.765 |
8 |
90.763 |
80.691 |
0.355 |
0.376 |
1.785 |
8 |
90.763 |
78.855 |
0.355 |
0.381 |
1.826 |
8 |
127.676 |
114.800 |
0.299 |
0.315 |
1.254 |
8 |
127.676 |
113.097 |
0.299 |
0.318 |
1.273 |
8 |
176.715 |
159.485 |
0.254 |
0.268 |
0.903 |
8 |
226.980 |
206.476 |
0.224 |
0.235 |
0.697 |
8 |
254.469 |
231.866 |
0.212 |
0.222 |
0.621 |
8 |
314.159 |
288.986 |
0.190 |
0.199 |
0.498 |
8 |
360 |
Diameter Nominal
Size External Internal (in) (in) (in)
|
3/4 |
1.050 |
0.742 |
0.154 |
1 |
1.315 |
0.957 |
0.179 |
1V4 |
1.660 |
1.278 |
0.191 |
1V2 |
1.900 |
1.500 |
0.200 |
2 |
2.375 |
1.939 |
0.218 |
2V2 |
2.875 |
2.323 |
0.276 |
3 |
3.500 |
2.900 |
0.300 |
3X/2 |
4.000 |
3.364 |
0.318 |
Dimensions of Extra-Strong Pipe
|
4 |
4.500 |
3.826 |
0.337 |
14.983 |
5 |
5.563 |
4.813 |
0.375 |
20.778 |
6 |
6.625 |
5.761 |
0.432 |
28.573 |
8 |
8.625 |
7.625 |
0.500 |
43.388 |
10 |
10.750 |
9.750 |
0.500 |
54.735 |
12 |
12.750 |
11.750 |
0.500 |
65.415 |
W O> |
15.904 |
11.497 |
0.848 |
0.998 |
12.525 |
24.306 |
18.194 |
0.686 |
0.793 |
7.915 |
34.472 |
26.067 |
0.576 |
0.663 |
5.524 |
58.426 |
45.663 |
0.442 |
0.500 |
3.154 |
90.063 |
74.662 |
0.355 |
0.391 |
1.929 |
[27.676 |
108.434 |
0.299 |
0.325 |
1.328 |
Nominal Size (in) |
Diameter |
Nominal Thickness (in) |
Nominal Weight Per Foot Plain Ends (lbs) |
Transverse Area |
Length of Pipe per Square Foot |
Length of Pipe Containing 1 Cubic Foot (ft) |
|||
External Surface (ft) |
Internal Surface (ft) |
||||||||
External (in) |
Internal (in) |
External (in2) |
Internal (in2) |
||||||
0.840 |
0.252 |
0.294 |
1.714 |
0.554 |
0.050 |
4.547 |
15.157 |
2887.165 |
|
3/4 |
1.050 |
0.434 |
0.308 |
2.440 |
0.866 |
0.148 |
3.637 |
8.801 |
973.404 |
1 |
1.315 |
0.599 |
0.358 |
3.659 |
1.358 |
0.282 |
2.904 |
6.376 |
510.998 |
M |
1.660 |
0.896 |
0.382 |
5.214 |
2.164 |
0.630 |
2.301 |
4.263 |
228.379 |
11/2 |
1.900 |
1.100 |
0.400 |
6.408 |
2.835 |
0.950 |
2.010 |
3.472 |
151.526 |
2 |
2.375 |
1.503 |
0.436 |
9.029 |
4.430 |
1.774 |
1.608 |
2.541 |
81.162 |
21/2 |
2.875 |
1.771 |
0.552 |
13.695 |
6.492 |
2.464 |
1.328 |
2.156 |
58.457 |
3 |
3.500 |
2.300 |
0.600 |
18.583 |
9.621 |
4.155 |
1.091 |
1.660 |
34.659 |
4 |
4.500 |
3.152 |
0.674 |
27.541 |
15.904 |
7.803 |
0.848 |
1.211 |
18.454 |
5 |
5.563 |
4.063 |
0.750 |
38.552 |
24.306 |
12.966 |
0.686 |
0.940 |
11.107 |
6 |
6.625 |
4.897 |
0.864 |
53.160 |
34.472 |
18.835 |
0.576 |
0.780 |
7.646 |
8 |
8.625 |
6.875 |
0.875 |
72.424 |
58.426 |
37.122 |
0.443 |
0.555 |
3.879 |
362 |
Wrought-steel pipe is cheaper than wrought-iron pipe and consequently is used more widely in heating, ventilating, and air-conditioning than the latter. Depending on the method of manufacture, wrought-steel pipe is available as either welded pipe or seamless pipe. Seamless wrought-steel pipe finds frequent application in high-pressure work.
The wall thickness and weights of wrought-steel pipe are approximately the same as those for wrought-iron pipe. As with wrought-iron pipe, the two most commonly used weights are standard and extra strong. Theoretical bursting and working pressures for wrought-steel pipe are listed in Table 8-4.
In some systems, steel piping has lasted as long as 80 years without showing signs of deterioration. When installed properly, steel piping and tubing are not subject to leakage. Most problems with floor systems occur with steel pipe or tubing installed in a single-pour slab. The stresses that can develop in this type of construction can sometimes damage the pipes or tubing in the radiant floor panels. This does not seem to be the case if the pipes or tubing is installed between the two sections of a two-pour slab or above a concrete slab and beneath a wood floor.
Armco plastic-coated steel, cold-rolled or extruded steel, and stainless steel are among the types of steels currently used in the manufacture of tubing for hydronic heating systems.
Galvanized steel or iron pipe is covered with a protective coating to resist corrosion. This type of pipe is often used underground or in other areas subject to corrosion. The coating is not permanent, and care should be used when handling it to avoid nicks and scratches. If the surface coating is broken, corrosion will begin that much sooner. Galvanized pipe is cheaper than copper pipe but more expensive than either wrought-iron or wrought-steel pipe.
Caution
Galvanized pipe and galvanized fittings are not recommended for use in steam heating systems.
Copper and Brass Pipes and Tubing
Copper and brass are used in the manufacture of both pipes and tubes and find their greatest application in air-conditioning, refrigeration, and hydronic radiant floor heating systems. One major advantage of using copper or brass is that both metals are corrosion resistant.
Table 8-4 Wrought-Steel PipeTheor etical Bursting and Working Pressures (pounds per square inch)*
|
364 |
Vs |
3 |
13,432 |
1679 |
18,760 |
2345 |
||
1/4 |
6 |
13,032 |
1629 |
17,624 |
2204 |
||
3/s |
10 |
10,784 |
1348 |
14,928 |
1866 |
||
1/2 |
13 |
10,384 |
1298 |
14,000 |
1750 |
28,000 |
3500 |
3/4 |
19 |
8,608 |
1076 |
11,728 |
1466 |
23,464 |
2933 |
1 |
25 |
8,088 |
1011 |
10,888 |
1361 |
21,776 |
2722 |
114 |
32 |
6,744 |
843 |
9,200 |
1150 |
18,408 |
2301 |
11/2 |
38 |
6,104 |
763 |
8,416 |
1052 |
16,840 |
2105 |
2 |
50 |
5,184 |
648 |
7,336 |
917 |
14,680 |
1835 |
212 |
64 |
5,648 |
706 |
7,680 |
960 |
15,360 |
1920 |
3 |
76 |
4,936 |
617 |
6,856 |
857 |
13,714 |
1714 |
312 |
90 |
5,610 |
701 |
7,950 |
994 |
15,900 |
1987 |
4 |
100 |
5,266 |
658 |
7,480 |
935 |
14,970 |
1871 |
412 |
113 |
4,940 |
618 |
7,100 |
887 |
14,200 |
1775 |
5 |
125 |
4,630 |
579 |
6,740 |
842 |
13,480 |
1685 |
6 |
150 |
4,220 |
528 |
6,520 |
815 |
13,040 |
1630 |
7 |
175 |
3,940 |
493 |
6,550 |
819 |
11,470 |
1434 |
8 |
200 |
3,730 |
466 |
5,780 |
722 |
10,140 |
1267 |
9 |
225 |
3,550 |
444 |
5,190 |
649 |
||
10 |
300 |
3,390 |
424 |
4,650 |
581 |
||
12 |
300 |
2,940 |
368 |
3,920 |
490 |
14 |
350 |
2,680 |
335 |
3,570 |
446 |
15 |
375 |
2,500 |
313 |
3,333 |
417 |
16 |
400 |
2,340 |
293 |
3,120 |
390 |
18 |
450 |
2,080 |
260 |
2,770 |
346 |
20 |
500 |
1,870 |
234 |
2,500 |
313 |
22 |
550 |
1,700 |
213 |
2,270 |
284 |
24 |
600 |
1,560 |
195 |
2,080 |
260 |
*Butt-welded pipe was figured on sizes 3 inches and smaller and lap-welded pipe on sizes 3 !/2 inches and larger. |
365 |
Sometimes the terms copper tube and copper pipe are used interchangeably as if they were synonymous. Another semantic idiosyncrasy is to refer to the same product as tube or tubing when still on the inventory at the supply house, but as pipe or piping when installed. Both usages can be confusing because there are differences between the two. For example, copper pipe is often made thicker than tubing because it can be used with threaded fittings if soldering is not desired for making the joint connection. Another point to remember is that copper pipes have the same outside diameters as standard steel pipes. Copper tubing, on the other hand, is standardized on the basis of use into three standard wall-thickness schedules (see Table 8-5): (1) Type K, (2) Type L, and (3) Type M. Type L and Type M are used in heating, ventilating, and air-conditioning systems.
Copper tubing is available as hard-grained (drawn) copper tubes or soft (annealed) copper tubes. The former is subject to freezing, which can cause the tubes to twist in almost the same way as steel pipes. On the other hand, the stiffness of hard-grained copper tubes enables them to hold their shape better than the softer ones. They are, therefore, often used for exposed lines such as mains hung from the ceiling.
The soft-tempered Type L copper tubing is recommended for hydronic radiant heating panels. Because of the relative ease with which soft copper tubes can be bent and shaped, they are especially well adapted for making connections around furnaces, boilers, oil-burning equipment, and other obstructions. This high workability characteristic of copper tubing also results in reduced installation time and lower installation costs. Copper tubing is produced in diameters ranging from V8 inch to 10 inches and in a variety of different wall thicknesses. Both copper and brass fittings are available. Hydronic heating systems use small tube sizes joined by soldering.
The DIN Rating System
Oxygen from the outside air can permeate the tubing material and enter the hydronic system where it will corrode iron and steel components (boiler, fittings, valves, and so on). In the early 1990s, American tubing manufacturers decided to adopt the German DIN Standard 4726 as a uniform rating system. DIN stands for Deutsche (German) Industry Norm. The DIN Standard 4726 requires that hydronic systems not permit the entry of more than one-tenth of a milligram of oxygen per liter of water per day when the water is 104°F (40°C). All of the tubing used in hydronic heating systems must meet this standard.
Pipes, Pipe Fittings, and Piping Details 367 Table 8-5 Sizes and Dimensions of Copper Water Tubes
For General |
||
For |
Plumbing and |
|
Underground |
House Heating |
|
Services and |
For General |
Purposes, with |
General |
Plumbing and |
Normal Water |
Plumbing |
House Heating |
Conditions. |
Purposes, Used |
Purposes, Used |
Used with |
With Solder or |
With Solder or |
Solder Fittings |
Flared Fittings |
Fittings |
Only |
Type Hard or |
Type Hard or |
Type Hard |
Sizes |
K |
Soft |
L |
Soft |
M |
||
Nominal Size (in) |
Outside Diameter (in) |
Wall Thick Ness |
Pounds Per Foot |
Wall Thick Ness |
Pounds Per Foot |
Wall Thick Ness |
Pounds Per Foot |
Vs |
0.250 |
0.032 |
0.085 |
0.025 |
0.068 |
0.025 |
0.068 |
1/4 |
0.375 |
0.032 |
0.133 |
0.030 |
0.126 |
0.025 |
0.106 |
3/s |
0.500 |
0.049 |
0.269 |
0.035 |
0.198 |
0.025 |
0.144 |
1/2 |
0.625 |
0.049 |
0.344 |
0.040 |
0.285 |
0.028 |
0.203 |
5/s |
0.750 |
0.049 |
0.418 |
0.042 |
0.362 |
0.030 |
0.263 |
3/4 |
0.s75 |
0.065 |
0.641 |
0.045 |
0.455 |
0.032 |
0.328 |
1 |
1.125 |
0.065 |
0.839 |
0.050 |
0.655 |
0.035 |
0.464 |
11/4 |
1.375 |
0.065 |
1.04 |
0.055 |
0.884 |
0.042 |
0.681 |
11/2 |
1.625 |
0.072 |
1.36 |
0.060 |
1.14 |
0.049 |
0.94 |
2 |
2.125 |
0.0s3 |
2.06 |
0.070 |
1.75 |
0.058 |
1.46 |
212 |
2.625 |
0.095 |
2.92 |
0.080 |
2.48 |
0.065 |
2.03 |
3 |
3.125 |
0.109 |
4.00 |
0.090 |
3.33 |
0.072 |
2.68 |
31/2 |
3.625 |
0.109 |
5.12 |
0.100 |
4.29 |
0.083 |
3.58 |
4 |
4.125 |
0.134 |
6.51 |
0.110 |
5.38 |
0.095 |
4.66 |
5 |
5.125 |
0.160 |
9.67 |
0.125 |
7.61 |
0.109 |
6.66 |
6 |
6.125 |
0.192 |
13.87 |
0.140 |
10.20 |
0.122 |
8.91 |
S |
S.125 |
0.271 |
25.90 |
0.200 |
19.29 |
0.170 |
16.46 |
10 |
10.125 |
0.33s |
40.26 |
0.250 |
30.04 |
0.212 |
25.57 |
12 |
12.125 |
0.405 |
57.76 |
0.280 |
40.36 |
0.254 |
36.69 |
Both cross-linked polyethylene tubing and polybutylene tubing are used in modern hydronic radiant panel heating systems. The former is by far the more popular of the two. The tubing is available in coils.
Some plastic tubing may become hardened and brittle after long use. If the tubing is then subjected to sudden unusual high pressures,
Such as those caused by boiler, valve, or other system component failures, cracks form and leakage occurs. Long cracks or fractures along a tubing circuit are not considered repairable to code.
Normal temperature differences in a hydronic system will cause the plastic tubing to expand and contract. This expansion and contraction over a long period of time eventually causes cracks or fractures to develop in the tubing, especially if it is already weakened by age or other factors. Expansion and contraction at the joints and connections between the tubing and the system boiler and manifolds may also cause leakage.
Cross-Linked Polyethylene Tubing
Cross-linked polyethylene (PEX) tubing is commonly used indoors in hydronic radiant heating panels or outdoors embedded beneath the surface of driveways, sidewalks, and patios to melt snow and ice. It is made of a high-density polyethylene plastic that has been subjected to a cross-linking process. It is flexible, durable, and easy to install. There are two types of PEX tubing:
Oxygen barrier tubing Nonbarrier tubing
Oxygen barrier tubing (BPEX) is treated with an oxygen barrier coating (EVOH) to prevent oxygen from passing through the tubing wall. It is designed specifically to prevent corrosion to any ferrous fittings or valves in the piping system. BPEX tubing is recommended for use in hydronic radiant heating system.
Nonbarrier tubing should be used in a hydronic radiant heating system only if it can be isolated from the ferrous components by a corrosion-resistant heat exchanger, or if only corrosion-resistant system components (boiler, valves, and fittings) are used.
PEX tubing is easy to install. Its flexibility allows the installer to bend it around obstructions and into narrow spaces. A rigid plastic cutter tool, or a copper tubing cutter equipped with a plastic cutting wheel, should be used to cut and install PEX tubing. Both tools produce a square cut without burrs.
Caution
PEX tubing is not resistant to ultraviolet (UV) rays. It should not be allowed to remain unprotected outdoors for long periods of time.
Polybutylene Tubing
Polybutylene tubing is offered in diameters and lengths comparable to PEX tubing but is more expensive, less durable, and not as easy to install.
Synthetic rubber hose is very flexible and highly temperature resistant, but it is less durable than PEX tubing and has a low pressure rating. A number of different rubbers have been used to produce synthetic rubber hose for use in hydronic systems. Cross-linked EPDM is one of the most popular types.
Some manufacturers are producing composite tubing for hydronic heating systems. Composite construction commonly involves the combination of aluminum sandwiched between layers of plastic (PEX) or synthetic rubber.
PAX tubing is a typical three-layer composite tubing consisting of an inner layer of PEX tubing, a middle layer of aluminum, and an outer layer of PEX tubing. The aluminum middle layer, which provides an effective barrier to oxygen penetration through the tubing walls, is bonded to the inner PEX layer. PEX tubing is very flexible and, because of its aluminum middle layer, will retain its shape after bending much more easily than standard PEX tubing or BPEX tubing. PAX tubing is recommended for use in hydronic floor panel heating systems.
Brass tube and brass pipe should also be distinguished from one another. Brass tubing is generally manufactured from yellow brass (about 65 percent copper, 35 percent zinc). Brass piping is more frequently a red brass (about 85 percent copper, 15 percent zinc) and is much stronger than the tubing. As a result, brass pipe is sometimes used in heating, ventilating, and air-conditioning systems, particularly when it is necessary to use a pipe material that strongly resists corrosion.
Pipe cannot be obtained in unlimited lengths. In most pipe installations, it is frequently necessary to join together two or more shorter lengths of pipe in order to create the longer one required by the blueprints. Furthermore, in practically all pipe installations there are numerous changes in directions and branches that require joining the pipes together in special arrangements. Pipe fittings have been devised for the necessary connections.
A pipe fitting may therefore be defined as any piece attached to pipes in order to lengthen a pipe, to alter its direction, to connect a branch to a main, to connect two pipes of different sizes, or to close an end.
Classification of Pipe Fittings
The pipe fittings used in heating, ventilating, and air-conditioning installations are most commonly either screwed or flanged types. Screwed pipe fittings use a male and female thread combination, which tightens together to form the joint. Screwed pipe fittings are designated as either male or female, depending on the location of the thread. A female thread is an internal thread, and a male thread is an external one.
A flanged pipe fitting has a lip or extension projecting at a right angle to its surface. This lip is bolted to the facing lip of the adjacent fitting for additional strength. As a result, flanged fittings are generally recommended for 4-inch pipe and above.
Screwed and flanged pipe fittings are used to make temporary joints. If soldering, brazing, or welding is used in joining the separate lengths of pipe, the joint is considered a permanent one. The advantage of a so-called temporary joint is that it can be easily disassembled for repair.
The great multiplicity of pipe fittings can be divided on the basis of their functions into the following six general classes:
Extension or joining fittings
• Reducing or enlarging fittings
• Directional fittings Branching fittings
• Union or makeup fittings Shutoff or closing fittings
Nipples, locknuts, couplings, offsets, joints, and unions are all examples of extension or joining fittings. With the possible exception of an offset, these fittings are designed to join and extend (but not change the direction of) a length of pipe. An offset is used to reposition a length of piping so that it is parallel but not in alignment with another section of its length. The offset itself constitutes a change of direction; however, its function is to create a piping run parallel but not in alignment with the rest of its length.
Nipples
Nipples are classified as close, short, or long (see Figure 8-3). Standard lengths of nipples are listed in Table 8-6. The length of close nipples varies with the pipe size, it being determined by the length of thread necessary to make a satisfactory joint. There is one length of
A |
/«1 111,1,1m 1UW
LONG NIPPLE |
CLOSE NIPPLE |
RIGHT — AND LEFT-HAND CENTER NIPPLE |
SHORT NIPPLE
|
THREADED END |
SHOULDER END GASKET UNION SCREW RING
GOOD ALIGNMENT |
GASKET
|
GROUND-JOINT UNION |
BAD ALIGNMENT j
|
Figure 8-3 Various pipe fittings used in heating and air-conditioning installations.
|
|
|
|
|
|
|
BLIND VARIOUS FLANGES |
Figure 8-3 (Continued) |
Short nipple for each size of pipe. Long nipples are made in many lengths up to 12 inches. Anything over 12 inches is known as cut pipe.
Locknuts
Locknuts are commonly used on long screw nipples that have couplings (see Figure 8-3). A recessed or grooved end on the locknut fitting is used to hold packing when a particularly tight joint is required. If at all possible, a union is preferred to a locknut because a much tighter joint is obtained.
The standard length for all sizes of locknut (or tank nipples) is 6 inches. They are made from standard-weight pipe threaded (for lock — nut) 4 inches long on one end and with regular pipe thread on the other. Tank nipples longer than 6 inches are made-to-order only.
Couplings
A coupling is a pipe fitting used to couple or connect two lengths of pipe. They are available in numerous sizes and types. The standard coupling (see Figure 8-3) is threaded with right-hand threads. Others are available with both right-hand and left-hand threads. The extension piece coupling illustrated in Figure 8-3 has a male thread at one end. Couplings used as reducers (see Figure 8-3) are also common.
Offsets
An offset fitting (see Figure 8-3) is used when it is necessary to pass the pipeline around an obstruction that blocks its path. The new path will be parallel to the old one, but not aligned with it.
Joints
A joint (also referred to as an expansion joint or bend) is a pipe fitting designed to accommodate the linear expansion and contraction of the pipe metal caused by the temperature differences between the water or steam inside the pipe and the air on the outside of it. The
Size (in) |
Standard Black, Right Hand Kind of Nipples |
||
V8 to V2 |
Close, short, then by |
Vi-inch lengths from 2 |
Inches long to 6 inches long |
Then by |
1-inch lengths from 6 |
Inches long to 12 inches long |
|
% and 1 |
Close, short, then by |
V2-inch lengths from 2V2 |
Inches long to 6 inches long |
Then by |
1-inch lengths from 6 |
Inches long to 12 inches long |
|
LVito 2 |
Close, short, then by |
V2-inch lengths from 3 |
Inches long to 6 inches long |
Then by |
1-inch lengths from 6 |
Inches long to 12 inches long |
|
21/2 and 3 |
Close, short, then by |
V2-inch lengths from 3V2 |
Inches long to 6 inches long |
Then by |
1-inch lengths from 6 |
Inches long to 12 inches long |
|
3V/2 and 4 |
Close, short, then by |
V2-inch lengths from 4V2 |
Inches long to 6 inches long |
Then by |
1-inch lengths from 6 |
Inches long to 12 inches long |
|
5 and 6 |
Close, short, then by |
V2-inch lengths from 5 |
Inches long to 6 inches long |
Then by |
1-inch lengths from 6 |
Inches long to 12 inches long |
|
8 |
Close, short, then by |
V2-inch lengths from 5V2 |
Inches long to 6 inches long |
Then by |
1-inch lengths from 6 |
Inches long to 12 inches long |
|
10 and 12 |
Close, short, then by |
1-inch lengths from 8 |
Inches long to 12 inches long |
376 |
Up to and including 8-inch size, same lengths as black, right hand
Standard Black, Right and Left Hand
Up to and including 4-inch size, same lengths as black, right hand
Extra Strong Black, Right Hand
377 |
Up to and including 2-inch size, same lengths as standard, black, right hand
Amount of expansion or contraction at different temperatures for a variety of metals used in steam pipes is listed in Table 8-7.
A union is another form of extension fitting used to join two pipes. The two most common types of unions are (1) the ground-joint union and (2) the plain or gasket union.
A ground-joint union (see Figure 8-3) consists of a composition ring pressing against iron or both contact surfaces of composition. A joint using a ground-joint union is characterized by spherical contact. Because no gasket is used, perfect alignment of the two pipes is not as important in making up the joint as it is when a plain or gasket union is used.
A disassembled plain or gasket union fitting is shown in Figure 8-3. It consists of three basic parts and a gasket. In assembling, the gasket (A) is placed over the projection on the shoulder so that it is in contact with its surface (B). The ring is slipped over the shoulder end and the threaded end placed in position so that the flat surface (C) of the threaded end presses against the gasket. The ring is then screwed firmly into the threaded end. Since the shoulder on the shoulder end cannot back off the ring, the two ends are pressed firmly together against the gasket by the ring, thus securing a tight joint.
The limitations of the plain or gasket union are also illustrated in Figure 8-3. The alignment must be good to secure a tight joint. In the illustration, the ring section is omitted for clearness. If both ends are in line and firmly pressed together against the gasket by the ring, the gasket will bear evenly over the entire contact surface and the joint will be tight. If the two ends are out of alignment when the ring is screwed tight, it will bring great pressure on the gasket at point A, and the surfaces will not come together at the opposite point B, thus causing a leak.
Reducing or Enlarging Fittings
Both bushings and reducers are examples of reducing or enlarging fittings. Their function in pipe installations is to connect pipes of different sizes.
Bushings and reducers may be distinguished by their construction. A reducer is a coupling device with female threads at both ends (see Figure 8-3). A bushing has both male and female threads.
A bushing (see Figure 8-3) is a pipe fitting designed in the form of a hollow plug, and it is used to connect the male thread of a pipe end to a fitting of larger size. Bushings are sold according to the pipe size of the male thread. Thus, a V4-inch bushing (or, more specifically, a
Table 8-7 Expansion of Pipe (Increase in Inches per 100 Feet)
Note: Expansion given is approximate but is correct to the best known information. The linear expansion and contraction of pipe, due to difference of temperature of the fluid carried and the surrounding air must be cared for by suitable expansion joints or bends. In order to determine the amount of expansion or contraction in a pipeline, Table 8-8 shows the increase in length of a pipe 100 feet long at various temperatures. The expansion for any length of pipe may be found by taking the difference in increased length at the minimum and maximum temperatures, dividing by 100, and multiplying by the length in feet of the line under consideration. |
379 |
V^inchXVs-inch bushing) is one used to connect a Vi-inch fitting to a Vs-inch pipe. This may be less confusing if you remember that a bushing has one male and one female thread and that the female thread of the bushing must be tightened into the male thread of the pipe end.
Ordinary bushings are sometimes used when a reducing fitting of proper size is unavailable. If the reduction is considerable, it may be necessary to use two bushings. A common application of eccentric bushings is to avoid water pockets on horizontal pipelines. This application is illustrated in Eliminating Water Pockets later in the chapter.
Directional fittings such as offsets, elbows, and return bends are used to change the direction of a pipe. Because of an overlap in function, offsets also may be considered to be a type of extension or joining fitting.
Elbows
An elbow (see Figure 8-3) is a pipe fitting used to change the direction of a gas, water, or steam pipeline. Elbows are available in standard angles of 45° and 90, or special angles of 22 V20 and 60° (see Figure 8-3).
Return Bends
A return bend (see Figure 8-3) is a U-shaped pipe fitting commonly used for making up pipe coils for both water and steam heating boilers. They are commonly available in three patterns (close, medium, and open) with female threads at both ends. It is important to know the dimensions between centers when making up heating coils in order to avoid possible interference.
As the name implies, a branching fitting is used to join a branch pipe to the main pipeline. The principal branching fittings used for this purpose are as follows:
Tees
Crosses
• Y branches
Elbows with side outlets
• Return bends with back or side outlets
Tees
Tees (see Figure 8-3) are made in a variety of sizes and patterns and represent the most widely used branch fitting. As the name suggests, a tee fitting is used for starting a branch pipe at a 90° angle to the main pipe.
A tee fitting is specified by first giving the run and then the branch. The run of a tee refers to its body with the outlets opposite each other (that is, at 180).
Tees are available with all three outlets the same size, with the branch outlet a size different from the two outlets of the run, or with all three outlets different sizes. Whatever the size configuration of outlets, the run is always specified first. Tee specifications generally take the following form:
• 1" (1-inch outlets on run and tee)
• 1" X V2" (1-inch outlets on run; V^-inch tee outlet)
• 1" X Vx (outlets of 1 inch and V2 inch on the run; y2-inch tee outlet)
A cross fitting (see Figure 8-3) is simply a tee with two branch outlets instead of one. The branch outlets are located directly opposite one another on the main pipe so that the fitting forms the shape of a cross (hence its name). Both branch outlets are always the same size, regardless of the size of the outlets.
A Ybranch (see Figure 8-3) is a pipe fitting with side outlets located at 45° or 60° angles to the main pipe. Y branches are available in a number of pipe sizes. They may be straight or reducing, and single — or double-branching.
An elbow with three outlets is classified as a branching rather than a directional fitting because the third outlet serves as the connection for a branch pipeline (see Figure 8-3). The branching outlet should be at a 90° angle to the plane of the elbow run.
Return Bends with Back or Side Outlets
An ordinary return bend is a U-shaped fitting with two outlets (see Figure 8-3). Some return bends are designed with three outlets, the third outlet being located on either the back or the side of the fitting and used for connecting to a branch pipeline. This type of return bend is more properly classified as a branching fitting.
Sometimes it is necessary to close the end of a fitting or pipe. This is accomplished with a shutoff or closing fitting, and the following two types are used for this purpose:
• Plugs
• Caps
Plugs
A plug (see Figure 8-3) is used to close the end of a pipe or fitting when it has a female thread. In other words, it is designed to be inserted into the end of the pipe or fitting. Plugs are made in a variety of sizes (V8 inch to 12 inches), designs (hexagon, square head, or countersunk heads), and materials (for example, iron, brass).
Caps
A cap (see Figure 8-3) performs the same function as a plug except that it is used to close the end of a pipe or fitting that has a male thread. They are also available in a variety of sizes, designs, and materials.
Union or makeup fittings (see Figure 8-3) are represented by union elbows and union tees. This type of pipe fitting combines both a union and an elbow or tee in a single unit. They are available with female or both male and female threads.
Flanges (see Figure 8-3) are pipe fittings used to close flanged pipelines or fittings. They are manufactured in the form of cast-iron discs and are available in many sizes, thicknesses, and types.
The linear expansion and contraction of pipe due to the surrounding air must be provided for (especially in the case of long lines) by suitable expansion joints, bends, or equivalent provisions.
In order to determine the amount of expansion or contraction in a pipeline, Table 8-8 shows the increase in length of a pipe 100 feet long at various temperatures.
The expansion for any length of pipe may be found by taking the difference in increased length at the minimum and maximum temperatures, dividing by 100, and multiplying by the length in feet of the line under consideration. See Table 8-8.
Expansion of Steam Pipes (Inches Increase per 100 Feet)
Steel 0 0.15 0.30 0.45 0.60 0.75 0.90 1.10 1.25 1.45 1.60 1.80 2.00 2.15 2.35 2.50 2.70 2.90 3.05 3.25 3.45 3.70 3.95 4.20 4.45 4.70 4.95 5.20 5.45 5.70 6.00 6.30 6.55 6.90 |
Temperature
(°F)
0
20
40
60
80
100
120
140
160
180
200
220
240
260
280
300
320
340
360
380
400
420
440
460
480
500
520
540
560
580
600
620
640
660
Wrought Iron
0
0.15
0.30
0.45
0.60
0.80
0.95
1.15
1.35
1.50
1.65
1.85
2.5 2.20
2.40
2.60
2.80
3.05
3.25
3.45
3.65
3.90
4.20
4.45
4.70
4.90
5.15
5.40
5.70
6.00
6.25
6.55
6.85
7.20
Cast Iron
0
0.10
0.30
0.40
0.55
0.75
0.85
1.00
1.15
1.30
1.50
1.65
1.80
1.95
2.15
2.35
2.50
2.70
2.90 3.10
3.30
3.50
3.75
4.00
4.25
4.45
4.70
4.95
5.20
5.45
5.70
5.95
6.25
6.55
Brass and Copper
0
0.25
0.45
0.65
0.90
1.15
1.40
1.65
1.90
2.15
2.40
2.65
2.90
3.15
3.45
3.75
4.05
4.35
4.65
4.95
5.25
5.60
5.95
6.30
6.65
7.05
7.45
7.85
8.25
8.65
9.05
9.50
9.95
10.40
(continued)
Temperature (°F) |
Steel |
Wrought Iron |
Cast Iron |
Brass and Copper |
680 |
7.20 |
7.50 |
6.85 |
10.95 |
700 |
7.50 |
7.85 |
7.15 |
11.40 |
720 |
7.80 |
8.20 |
7.45 |
11.90 |
740 |
8.20 |
8.55 |
7.80 |
12.40 |
760 |
8.55 |
8.90 |
8.15 |
12.95 |
780 |
8.95 |
9.30 |
8.50 |
13.50 |
800 |
9.30 |
9.75 |
8.90 |
14.10 |
Some authorities regard a valve as simply another type of pipe fitting and distinguish it from others by its capacity to control the flow of steam or hot water through the pipe. Be that as it may, the subject of valves is so extensive that it warrants a chapter of its own (see Chapter 9 of Volume 2, V alves and Valve Installation)’.
The threads used on pipes are referred to as pipe threads. The distinguishing characteristic of pipe threads is that they are tapered. This results in a greater number of turns when screwing the pipe to another length of pipe or pipe fitting. When properly done, this will result in a tight, leak-free joint. Care must be taken, however, not to exceed the elastic limit or the joint will leak.
The total taper used on pipe threads in % inch per foot. The total number of threads per inch will vary from 27 threads for V8-in pipe to 8 threads for 2y2-in pipe and larger sizes. Standard pipe threads are listed in Table 8-9.
Pipe sizing refers to the procedure of determining the projected capacities of a piping installation and selecting the pipe sizes most capable of meeting these capacities. Most methods used for determining pipe sizes are only approximate calculations, and they should be considered as such when you are using them.
Both the American Society of Heating, Refrigerating, and Air — Conditioning Engineers (ASHRAE) and the Institute of Boiler and Radiator Manufacturers (IBR) issue publications that contain considerable data for designing the piping arrangements of various steam and hot-water space heating systems. Manufacturers of proprietary heating systems, pipes, pipe fittings, and valves also provide data for sizing pipes and valves. Examples of these data are illustrated in Tables 8-10 and 8-11. Methods for pipe sizing are explained in detail with accompanying examples. These publications can be obtained by writing to these organizations. Their addresses are given elsewhere in this book. Sometimes copies are also available at a local library.
Because pipe sizing is specific to the piping arrangement and other variables within a system, no attempt is made in this chapter to cover the subject with the detail it requires. The basic principles of the methods used for sizing steam and hot-water heating pipes, along with recommendations for their application, are described in the sections that follow.
Many manufacturers of proprietary or patented steam heating systems provide their own pipe-sizing schedules. For nonproprietary systems, the projected capacities of the piping installation must be determined by a number of sizing calculations.
The principal factors used in determining pipe sizes for a given load of steam in a heating system are the following:
Initial pressure
Total pressure drop allowed between the boiler and the end of the return line
Equivalent length of run from the boiler to the farthest radiator or convector
• Pressure drop per 100 feet of equivalent length
The total pressure drop should not exceed the initial gauge pressure of the system. As a general rule, it should not exceed 50 percent of the initial gauge pressure.
The equivalent length of run equals the actual measured length of pipe plus the equivalent straight pipe length of the fittings and valves. Table 8-12 lists equivalent lengths of the more common fittings and valves and is an example of the data provided by the ASHRAE for sizing pipes.
The pressure drop in pounds per square inch per 100 feet is determined by dividing 50 percent of the initial pressure by the equivalent length of the longest piping circuit.
For the sake of illustration, assume that you must calculate the pressure drop and determine the pipe size for a steam heating
A |
B |
E |
F |
G |
H |
P |
|||
Nominal |
Pitch Dia. at |
Pitch Dia. at |
Length Of |
Normal Engagement by Hand Between Male and |
Outside |
Actual Inside |
Number Of Threads |
Pitch |
Depth |
Size |
End of |
Gauging |
Effective |
Female |
Dia. of |
Dia. of |
Per |
Of |
Of |
Of Pipe |
Pipe |
Notch |
Thread |
Thread |
Pipe |
Pipe |
Inch |
Thread |
Thread |
(in) |
(in) |
(in) |
(in) |
(in) |
(in) |
(in) |
(in) |
(in) |
|
Vs |
0.36351 |
0.37476 |
0.2638 |
0.180 |
0.405 |
0.269 |
27 |
0.0370 |
0.02963 |
X/4 |
0.47739 |
0.48989 |
0.4018 |
0.200 |
0.540 |
0.364 |
18 |
0.0556 |
0.04444 |
3/s |
0.61201 |
0.62701 |
0.4078 |
0.240 |
0.675 |
0.493 |
18 |
0.0556 |
0.04444 |
12 |
0.75843 |
0.77843 |
0.5337 |
0.320 |
0.840 |
0.622 |
14 |
0.0714 |
0.05714 |
3/4 |
0.06768 |
0.98886 |
0.5457 |
0.339 |
1.050 |
0.824 |
14 |
0.0714 |
0.05714 |
1 |
1.21363 |
1.23863 |
0.6828 |
0.400 |
1.315 |
1.049 |
11V2 |
0.0870 |
0.06954 |
L1/4 |
1.55713 |
1.58338 |
0.7068 |
0.420 |
1.660 |
1.380 |
11V2 |
0.0870 |
0.06954 |
11/2 |
1.79609 |
1.82234 |
0.7235 |
0.420 |
1.900 |
1.610 |
11V2 |
0.0870 |
0.06956 |
2 |
2.26902 |
2.29627 |
0.7565 |
0.436 |
2.375 |
2.067 |
111/2 |
0.0870 |
0.06956 |
2V2 |
2.71953 |
2.76216 |
1.1375 |
0.681 |
2.875 |
2.469 |
8 |
0.1250 |
0.10000 |
386 |
3 |
3.34063 |
3.38850 |
1.2000 |
0.766 |
3V2 |
3.83750 |
3.88881 |
1.2500 |
0.821 |
4 |
4.33438 |
4.38713 |
1.3000 |
0.844 |
4V2 |
4.83125 |
4.88594 |
1.3500 |
0.875 |
5 |
5.39073 |
5.44929 |
1.4063 |
0.937 |
6 |
6.44609 |
6.50597 |
1.5125 |
0.958 |
7 |
7.43984 |
7.50234 |
1.6125 |
1.000 |
8 |
8.43359 |
8.50003 |
1.7125 |
1.063 |
9 |
9.42734 |
9.49797 |
1.8125 |
1.130 |
10 |
10.54531 |
10.62094 |
1.9250 |
1.210 |
12 |
12.53281 |
12.61781 |
2.1250 |
1.360 |
14 O. D. |
13.77500 |
13.87262 |
2.250 |
1.562 |
15 O. D. |
14.76875 |
14.87419 |
2.350 |
1.687 |
16 O. D. |
15.76250 |
15.87575 |
2.450 |
1.812 |
18 O. D. |
17.75000 |
17.87500 |
2.650 |
2.000 |
20 O. D. |
19.73750 |
19.87031 |
2.850 |
2.125 |
22 O. D. |
21.72500 |
21.86562 |
3.050 |
2.250 |
24 O. D. |
23.71250 |
23.86094 |
3.250 |
2.375 |
Data abstracted from the American Standard for Pipe Threads A. SA.-B2—1919. |
3.500 |
3.068 |
8 |
4.000 |
3.548 |
8 |
4.500 |
4.026 |
8 |
5.000 |
4.506 |
8 |
5.563 |
5.047 |
8 |
6.625 |
6.055 |
8 |
7.625 |
7.023 |
8 |
8.625 |
7.981 |
8 |
9.625 |
8.941 |
8 |
10.750 |
10.020 |
8 |
12.750 |
12.000 |
8 |
14.000 |
— |
8 |
15.000 |
— |
8 |
16.000 |
— |
8 |
18.000 |
— |
8 |
20.000 |
__ |
8 |
22.000 |
— |
8 |
24.000 |
— |
8 |
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0.1250 0.10000
0. 1250 0.10000
0. 1250 0.10000
0. 1250 0.10000
— IMPERFECT — THREAD DUE TO LEAD OF DIE |
NORMAL ENGAGEMENT BY HAND BETWEEN MALE AND FEMALE THREAD |
LENGTH OF EFFECTIVE THREADS ———————————— E—————————- |
I |
■3os, |
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A = G — (0.05 G + 1.1)P B = A + 0.0625 F E = P (0.8G + 6.8)
DEPTH OF THREAD = 0.8P TOTAL TAPER ^"-IN. PER FOOT
Illustration for Table 8-9.
System in which the initial pressure is 2 psig. In order to do this, the following steps are necessary:
Pipe Size (in) |
Internal Diameter D (in) |
Pipe Size |
In Inches |
|||||||||||||||||
D5/‘ |
1 8 |
1 4 |
3 8 |
1 2 |
3 4 |
1 |
1 [3] 4 |
1 1 2 |
2 |
21 2 |
3 |
31 2 |
4 |
5 |
6 |
8 |
10 |
12 |
||
Vs |
0.269 |
0.037530 |
1.0 |
|||||||||||||||||
V4 |
0.364 |
0.079938 |
2.1 |
1.0 |
||||||||||||||||
3/8 |
0.493 |
0.17065 |
4.5 |
2.1 |
1.0 |
|||||||||||||||
12 |
0.622 |
0.30512 |
8.1 |
3.8 |
1.8 |
1.0 |
||||||||||||||
3/4 |
0.824 |
0.61634 |
16 |
7.7 |
3.6 |
2.0 |
1.0 |
|||||||||||||
1 |
1.049 |
1.1270 |
30 |
14 |
6.6 |
3.7 |
3.7 |
1.0 |
||||||||||||
1/4 |
1.380 |
2.2372 |
60 |
28 |
13 |
7.3 |
3.6 |
2.0 |
1.0 |
|||||||||||
11/2 |
1.610 |
3.2890 |
88 |
41 |
19 |
11 |
5.3 |
2.9 |
1.5 |
1.0 |
||||||||||
2 |
2.067 |
6.1426 |
164 |
77 |
36 |
20 |
10 |
5.5 |
2.7 |
1.9 |
1.0 |
|||||||||
21/2 |
2.469 |
9.5786 |
255 |
120 |
56 |
31 |
16 |
8.5 |
4.3 |
2.9 |
1.6 |
1.0 |
||||||||
3 |
3.068 |
16.487 |
439 |
206 |
97 |
54 |
27 |
15 |
7.4 |
5.0 |
2.7 |
1.7 |
1.0 |
|||||||
31/2 |
3.548 |
23.711 |
632 |
297 |
139 |
78 |
38 |
21 |
11 |
7.2 |
3.9 |
2.5 |
1.4 |
1.0 |
||||||
4 |
4.026 |
32.523 |
867 |
407 |
191 |
107 |
53 |
29 |
15 |
9.9 |
5.3 |
3.4 |
2.0 |
1.4 |
1.0 |
|||||
5 |
5.047 |
57.225 |
1526 |
716 |
335 |
188 |
93 |
51 |
26 |
17 |
9.3 |
6.0 |
3.5 |
2.4 |
1.8 |
1.0 |
— |
— |
— |
— |
6 |
6.065 |
90.589 |
2414 |
1163 |
531 |
297 |
147 |
80 |
40 |
28 |
15 |
9.5 |
5.5 |
3.8 |
2.8 |
1.6 |
1.0 |
— |
— |
— |
8 |
7.981 |
179.95 |
4795 |
2251 |
1054 |
590 |
292 |
160 |
80 |
55 |
29 |
19 |
11 |
7.6 |
5.5 |
3.1 |
2.0 |
1.0 |
— |
— |
10 |
10.020 |
317.81 |
8468 |
3976 |
1862 |
1042 |
516 |
282 |
142 |
97 |
52 |
33 |
19 |
13 |
9.8 |
5.6 |
3.5 |
1.8 |
1.0 |
— |
12 |
12.000 |
498.83 |
13292 |
6240 |
2923 |
1635 |
809 |
443 |
223 |
152 |
81 |
52 |
30 |
21 |
15 |
8.7 |
5.5 |
2.8 |
1.6 |
1.0 |
The figure that lies at the intersection of any two sizes is the number of smaller-size pipes required to equal one of the larger. Example: How many 2-inch standard pipes will it take to equal the discharge of one 8-inch standard pipe? Solution:Twenty-nine 2-inch pipes; the figure in the table that lies at the intersection of these two sizes is 29. |
389 |
Table 8-11 Diagram Showing Resistance of Valves and Fittings of the Flow of Liquids
ORDINARY ENTRANCE |
■ -45° ELBOW |
48- |
42- |
36- |
30 |
30 |
24—’ |
22 |
■20 |
20 — 1-—- 16 — |
14 |
12 |
10 |
10 |
INSIDE DIAMETER, INCHES |
9 |
8 |
SUDDEN ENLARGEMENT d/D-1/4 d/D-!/2 D/D- |
7 |
6- |
5 |
41/2 |
4 |
3 |
3 |
< CD < |
21/2 |
2-1 |
2 |
SUDDEN CONTRACTION d/D-M d/D-V2 d/D-5’4 |
11/2 |
11/4 |
; 1000 -500 ■ 300 — 200 100 LL LL ■" 50 “ — Q * Q -30 h 20, -10 |
-5 ; . I ■3 ; -2 ; I -■1 " 0.5 " 0.3 -0.2 -0.1 |
50 |
|
|
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Table 8-12 Length of Pipe in Feet for Fittings to Be Added to Actual Length of Run in Order to Obtain Equivalent Length
|
*Valve in full open position. Example of length in
|
6. Check the pressure drop by calculating the equivalent length of run of the longest circuit from the pipe sizes determined. The pipe size determined in step 5 will be correct if the calculated pressure drop is less than the assumed pressure drop.
A steam supply main should not pitch less than Vi inch per 10 feet of run, and its diameter should not be smaller than 2 inches. In
Gravity one-pipe systems, the diameter of the supply main at the farthest point should not be smaller than 50 percent of its largest diameter.
A rule-of-thumb method for determining the size of steam mains is to take the total amount of direct radiation and add to it 25 percent of the total for the piping allowance. Next, find the square root of this total and divide by 10. The result will be the size steam main to use for a one-pipe system. For a two-pipe system, one size smaller is generally sufficient for the supply main, and the return can be one or two sizes smaller than the supply main. A steam main should not decrease in size according to the area of its branches but much more gradually.
The aforementioned method for sizing steam mains can be illustrated by using a structure with an assumed direct radiation of 500 square feet. Adding 25 percent for piping allowance gives 625. The square root of 625 is 25, which divided by 10 gives 2V2, or the size of the steam main (2V2 inches). For reference and practical use, refer to Table 8-13 when making calculations.
The pitch of runouts to risers and radiators should be at least V2 inch per foot toward the main. Runouts over 8 feet in length but with less than Vi-inch pitch per foot should be one size larger than specified in the pipe-sizing tables.
Table 8-13 Size of Steam Mains
|
Sizing Hot-Water (Hydronic) Pipes/Tubing
Simplified pipe-sizing tables for hot-water heating systems are also available from organizations such as the ASHRAE.
Pipe sizing hot-water lines is similar in some respects to the calculations used in duct sizing because the pipe sizes are selected on the basis of the quantity and rate of water flow (expressed in gallons per minute, or gpm) and the constant friction loss. This friction loss (or drop) is expressed in thousandths-of-an-inch per foot of pipe length.
The velocity of water in the smaller residential pipes should not exceed 4 fps (feet per second), or there will be a noise problem.
In forced hot-water heating systems, the problem of friction drop in the pipes can be overcome by the pump or circulator. In this respect, a forced hot-water heating system is much easier to size than a steam heating system.
The rule-of-thumb method used to size steam mains (see previous section) can also be used to determine the approximate sizes of hot — water mains; however, certain important differences should be noted.
When sizing hot-water mains, the mains may be reduced in size in proportion to the branches taken off. They should, however, have as large an area as the sum of all branches beyond this point. It is advisable that the horizontal branches be one size larger than the risers. Returns should be the same size as the supply mains. Table 8-14 lists sizes of hot-water mains and the equivalent radiation ranges in square feet. Sizes for mains and branches are given in Table 8-15.
Table 8-14 |
Sizes of Hot-Water Mains |
Radiation (ft2) |
Pipe (in) |
75 to 125 |
114 |
125 to 175 |
11/2 |
175 to 300 |
2 |
300 to 475 |
21/2 |
475 to 700 |
3 |
700 to 950 |
31/2 |
950 to 1200 |
4 |
1200 to 1575 |
41/2 |
1575 to 1975 |
5 |
1975 to 2375 |
51/2 |
2375 to 2850 |
6 |
Main |
Branch
1 inch will supply 1V4 inch will supply 1V2 inch will supply
2 inch will supply
2 V2 inch will supply
3 inch will supply 3V2 inch will supply
4 inch will supply 4V2 inch will supply
5 inch will supply
6 inch will supply
7 inch will supply
8 inch will supply
2, 3/4 inch 2, 1 inch 2, 1V4 inches 2, 1V2 inches
2, 1V2 inches and 1, 1V4 inches, or 1, 2 inches and 1, 1V4 inches
1, 2V2 inches and 1, 2 inches, or 2, 2 inches and 1, 1V2 inches
2, 2V2 inches or 1, 3 inches, and 1, 2 inches or 3, 2 inches
1, 3V2 inches and 1, 2V2 inches, or 2, 3 inches and 4, 2 inches 1, 3V2 inches and 1, 3 inches, or 1, 4 inches and 1, 2V2 inches 1, 4 inches and 1, 3 inches, or
1, 4V2 inches and 1, 2V2 inches
2, 4 inches and 1, 3 inches, or
4, 3 inches or 10, 2 inches
1, 6 inches and 1, 4 inches, or
3, 4 inches and 1, 2 inches
2, 6 inches and 1, 5 inches, or
5, 4 inches and 2, 2 inches
WIDTH OF ROOM 22 21 20 19 18 17 16 15 14 13 12 11 |
YBRANCH |
, * THREAD fi-. s ‘d3EngagemenT^;v,^| |
SERVICE TEE CROSS |
&A ^ Ja 10° ELBOW 45° ELBOW 90° STREET ELBOW45° STREET ELBO’" omw. nr-rrr □W. Lui w ‘_j! j ‘ |
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Size (in) |
General dimentions of Crane standard malleable iron screwed fittings. The reference letters refer to the accompanying table.
395 |
Dimensions (in)
Vs |
“/16 |
3/4 |
— |
— |
1 |
7/8 |
— |
11/16 |
— |
— |
— |
— |
31/32 |
14 |
13/16 |
3/4 |
— |
— |
13/16 |
15/16 |
11/4 |
11/16 |
— |
— |
— |
— |
11/16 |
3/8 |
15/16 |
13/16 |
— |
— |
17/16 |
11/32 |
11/4 |
11/16 |
— |
— |
123/32 |
215/32 |
15/32 |
V2 |
11/8 |
7/8 |
13/4 |
17/8 |
15/8 |
15/32 |
13/8 |
25/32 |
11/8 |
11/2 |
123/32 |
215/32 |
111/32 |
3/4 |
15/16 |
1 |
21/32 |
25/16 |
17/8 |
15/16 |
17/16 |
11/32 |
13/8 |
2 |
21/16 |
27/8 |
11/2 |
1 |
11/2 |
11/8 |
25/16 |
225/32 |
21/8 |
115/32 |
111/16 |
17/32 |
13/4 |
21/2 |
27/16 |
33/8 |
111/16 |
1V4 |
13/4 |
15/16 |
213/16 |
35/16 |
27/16 |
123/32 |
21/16 |
19/32 |
21/8 |
3 |
215/16 |
43/32 |
115/16 |
11/2 |
115/16 |
17/16 |
33/16 |
311/16 |
211/16 |
17/8 |
25/16 |
111/32 |
21/2 |
31/2 |
39/32 |
417/32 |
25/32 |
2 |
214 |
111/16 |
37/8 |
41/4 |
31/4 |
77/32 |
25/8 |
17/16 |
23/4 |
4 |
4I/32 |
517/32 |
217/32 |
21/2 |
211/16 |
115/16 |
— |
55/32 |
4 |
— |
31/16 |
2 |
— |
41/2 |
43/4 |
61/2 |
27/8 |
3 |
31/16 |
23/16 |
— |
513/16 |
411/16 |
— |
39/16 |
21/8 |
— |
5 |
511/16 |
73/4 |
31/2 |
31/2 |
327/32 |
219/32 |
— |
— |
— |
— |
4 |
23/16 |
— |
— |
— |
— |
— |
4 |
313/16 |
25/8 |
— |
615/16 |
511/16 |
— |
43/8 |
25/16 |
— |
6 |
615/16 |
9 |
45/16 |
5 |
51/2 |
31/16 |
— |
615/16 |
— |
— |
51/8 |
217/32 |
— |
— |
— |
— |
— |
6 |
51/8 |
315/32 |
— |
— |
— |
— |
57/8 |
211/16 |
— |
— |
— |
— |
— |
General dimensions of Crane standard malleable iron screwed fittings. |
DISTANCE CENTER TO FACE
-■bZ
72222m^2222222222222222222222222222222222222222222. |
ACTUAL LENGTH OF PIPE D — |
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D = A — 2B + 2C
Figure 8-4 Diagram showing how to obtain the actual length of a pipe connecting two fittings.
Figure 8-5 Joint made up showing length of thread on pipe
(A) screwed into fitting.
Pipe fitting may be done either by making close visual judgments or entirely by measurements scaled on a drawing. The first method is a hit-or-miss process and requires an experienced fitter to do a good job; the second method is one of precision and is the better way. In actual practice, a combination of the two methods will, in some cases, save time and give satisfactory results.
Working from a drawing with all the necessary dimensions has certain advantages. Especially in the case of a big job, all the pipe may be cut and threaded in the shop so that at the place of installation the only work to be done is assembling.
In making a drawing, the measurements are based on the distances between the centers of fittings. The data necessary to locate these centers are given in a more general dimension drawing with an accompanying table such as the one illustrated in Table 8-16. These dimension drawings and tables should be the ones corresponding to the make of fittings used; otherwise, there might be the possibility of
slight variation. In general, however, the different makes are pretty well standardized.
Figure 8-4 illustrates how the actual length of pipe connecting the two fittings is obtained. The actual length of pipe is equal to the distance between centers (of fittings) minus twice the distance from the center of the face of the fittings plus twice the allowance for threads. This is expressed by the following equation:
D = A — 2B + 2C
The allowance for the length of thread that is screwed into the fitting (dimension C in Figure 8-4) is obtained from a table furnished by the manufacturer. This allowance (called A in Figure 8-5) corresponds to the values given in the accompanying table (see Table 8-17). Note that the dimension A in Figure 8-5 is the same as dimension C in Figure 8-4.
A working drawing showing centerlines and distances between centers of an installation is shown in Figure 8-6. This gives all the information except the actual length of the pipes.
Problem
Find the length of the pipe connecting the 2-inch elbows in Figure 8-7. Using Figure 8-4 as a guide, the following dimensions are provided: A = 12 ft, B = 21/4 in, and C = n/16 in. The problem is solved as follows:
1. D = A-2B + 2C
2. D = 12 ft—2 X 2V4 in + 2 X 11/16 in
3. D = 12 ft-4Vi in + 22/32 (or 13/8) in
4. D = 11 ft 7V2 in + 13/8 in
5. D = 11 ft 8% in
In pipe fitting, an offset is a change of direction (other than 90°) in a pipe bringing one part out of (but parallel with) the line of another.
An example of an offset is illustrated in Figure 8-8. As shown here, the problem is an obstruction (E), such as a wall, blocking the path of a pipeline (L). It is necessary to change the position of pipeline L at point A to some parallel position such as line F in order to move around the obstruction. When two lines such as L and F are to be piped with elbows other than 90° elbows, the pipe fitter is confronted with the following two problems: (1) finding the length of pipe H and (2) determining the distance BC. By determining the distance BC, the pipe fitter will be able to fix point A so that the two elbows A and C will be in alignment.
Table 8-17 Length of Thread on Pipe
|
398 |
Between centers of an installation. |
|
Figure 8-8 Pipeline connected with two 45° elbows illustrating offsets and method of finding length of connecting pipe H. |
Of course, in the triangle ABC, the length of pipe AC and either offset (AB or BC) that may be required are quickly calculated by solving the triangle ABC for the desired member, but this involves taking the square root, which is not always easily understood by the average worker. Alternative methods are suggested in the following sections.
If, in Figure 8-8, the distance between pipelines L and F is 20 inches (offset AB), what length of pipe H is required to connect with the 45° elbows A and C?
Based on the triangle ABC, the following equation is offered for solving this problem:
1. AC2 = AB2 + BC2 from which:
2. AC = VAB2 = BC2 or substituting:
3. AC = V202 + 202 = V800 = 28.28 inches
It should be remembered that when 45° elbows are used, both offsets are equal. Therefore, if offset AB is 20 inches long, offset BC also must be the same length.
Note that the value (that is, 28.28 inches) for the length of pipe H obtained by the aforementioned equation is the calculated length and does not allow for the projections of the elbows. In other words, pipe H (as calculated by this equation) is too long and must be shortened so that the elbows will fit.
Figure 8-8 illustrates the difference between the calculated length (that is, the measurement from point A to point C) and the actual length of connecting pipe H when used with elbows other than 90°. Actual length is obtained by deducting the allowance for projection of the elbows from the calculated length. |
Another method of calculating the connecting pipe length (that is, the length of pipe H in Figure 8-9) is by multiplying the offset by 53/128 inch and adding the product to the original offset figure. Thus, if offset AB is 20 inches, the following calculations are possible:
. 53 1060 „ 9
‘ X 128 = 128 = 32
99
32 32
The pipe fitter will often encounter elbows of angles other than 45°. For these, the distance between elbow centers (points A and C) can easily be calculated with the following procedure:
1. Determine the angle of the elbow.
2. Determine the elbow constant equivalent to its angle.
3. Multiply the elbow constant by the known offset.
|
In Figure 8-10, even though only offset AB is known, it is possible to determine the length of the other offset (BC) and the distance between elbow centers (AC). In order to do this, the following equations must be used:
AC = offset AB X constant for AC BC = offset AB X constant for AB
Assume that the distance between pipelines L and F (offset AB) in Figure 8-10 is 20 inches and the angle of the elbow is 22y2°. In Table 8-18 you will find that for a 22V20 elbow, the elbow constant for AB is 2.41. Substituting values in the second equation, you have the following:
BC = 20 X 2.61 = 48.2 inches
The constant for the elbow centers of 221/2° elbows is 2.61. Substituting values in the first equation gives the following results:
AC = 20 X 2.61 = 52.2 inches
Table 8-18 Elbow Constants
|
Offsets may also be calculated by using basic trigonometry. Using the example given in Figure 8-10, determine the length of the offset AB if AC is 8 feet and the angle ^ = 60°. From Table 8-19, sine 60° = 0.866:
Length of offset AB = 0.866 X 8 = 6.93
If piping is to be run along the wall or ceiling, it should be attached to the surface with pipe supports (for example, hangers, straps, clamps). The type of pipe supports used and their spacing will be regulated in accordance with approved local standards.
Pipe straps (perforated metal straps) are used to support small size pipes (see Figure 8-11). Larger pipes require various types of hangers (for example, rod, spring), chains, or other devices capable of supporting the heavier weight.
Vertical pipe is best supported with a shoulder clamp attached to the flooring at the point through which the pipe passes, or by clamps attached to adjacent walls or columns.
Pipe hangers and anchors are also used for supporting suspended piping or securing it (as in the case of anchors) to adjacent surfaces. Hangers are similar in appearance and function to pipe straps (see previous).
Joint compound (also referred to as pipe dope) is a substance applied to the male thread when making up screwed joints. The purpose of applying a joint compound is to lubricate the threads so that tightening is made easier. By lubricating the threads, the friction and heat produced by the tightening operation are greatly
|
Deg |
Sin |
Cos |
Tan |
Sec |
Deg |
Sin |
Cos |
Tan |
Sec |
0 |
0.00000 |
1.0000 |
0.00000 |
1.0000 |
46 |
0.7193 |
0.6947 |
1.0355 |
1.4395 |
1 |
0.01745 |
0.9998 |
0.01745 |
1.0001 |
47 |
0.7314 |
0.6820 |
1.0724 |
1.4663 |
2 |
0.03490 |
0.9994 |
0.03492 |
1.0006 |
48 |
0.7431 |
0.6691 |
1.1106 |
1.4945 |
3 |
0.05234 |
0.9986 |
0.05241 |
1.0014 |
49 |
0.7547 |
0.6561 |
1.1504 |
1.5242 |
4 |
0.06976 |
0.9976 |
0.06993 |
1.0024 |
50 |
0.7660 |
0.6428 |
1.1918 |
1.5557 |
5 |
0.08716 |
0.9962 |
0.08749 |
1.0038 |
51 |
0.7771 |
0.6293 |
1.2349 |
1.5890 |
6 |
0.10453 |
0.9945 |
0.10510 |
1.0055 |
52 |
0.7880 |
0.6157 |
1.2799 |
1.6243 |
7 |
0.12187 |
0.9925 |
0.12278 |
1.0075 |
53 |
0.7986 |
0.6018 |
1.3270 |
1.6618 |
8 |
0.1392 |
0.9903 |
0.1405 |
1.0098 |
54 |
0.8090 |
0.5878 |
1.3764 |
1.7013 |
9 |
0.1564 |
0.9877 |
0.1584 |
1.0125 |
55 |
0.8192 |
0.5736 |
1.4281 |
1.7434 |
10 |
0.1736 |
0.9848 |
0.1763 |
1.0154 |
56 |
0.8290 |
0.5592 |
1.4826 |
1.7883 |
11 |
0.1908 |
0.9816 |
0.1944 |
1.0187 |
57 |
0.8387 |
0.5446 |
1.5399 |
1.8361 |
12 |
0.2079 |
0.9781 |
0.2126 |
1.0223 |
58 |
0.8480 |
0.5299 |
1.6003 |
1.8871 |
13 |
0.2250 |
0.9744 |
0.2309 |
1.0263 |
59 |
0.8572 |
0.5150 |
1.6643 |
1.9416 |
14 |
0.2419 |
0.9703 |
0.2493 |
1.0300 |
60 |
0.8660 |
0.5000 |
1.7321 |
2.0000 |
15 |
0.2588 |
0.9659 |
0.2679 |
1.0353 |
61 |
0.8746 |
0.4848 |
1.8040 |
2.0627 |
16 |
0.2756 |
0.9613 |
0.2867 |
1.0403 |
62 |
0.8820 |
0.4695 |
1.8807 |
2.1300 |
17 |
0.2924 |
0.9563 |
0.3057 |
1.0457 |
63 |
0.8910 |
0.4540 |
1.9626 |
2.2027 |
18 |
0.3090 |
0.9511 |
0.3249 |
1.0515 |
64 |
0.8988 |
0.4384 |
2.0503 |
2.2812 |
19 |
0.3256 |
0.0455 |
0.3443 |
1.0576 |
65 |
0.9063 |
0.4226 |
2.1445 |
2.3662 |
20 |
0.3420 |
0.9397 |
0.3640 |
1.0642 |
66 |
0.9135 |
0.4067 |
2.2460 |
2.4586 |
21 |
0.3584 |
0.9336 |
0.3839 |
1.0711 |
67 |
0.9205 |
0.3907 |
2.3559 |
2.5593 |
404 |
22 |
0.3746 |
0.0272 |
0.4040 |
1.0785 |
23 |
0.3907 |
0.9205 |
0.4245 |
1.0664 |
24 |
0.4087 |
0.9135 |
0.4452 |
1.0846 |
25 |
0.4220 |
0.9063 |
0.4663 |
1.1034 |
26 |
0.4386 |
0.8938 |
0.4877 |
1.1126 |
27 |
0.4540 |
0.8910 |
0.5095 |
1.1223 |
28 |
0.4695 |
0.8829 |
0.5317 |
1.1326 |
29 |
0.4848 |
0.8746 |
0.5543 |
1.1433 |
30 |
0.5000 |
0.8660 |
0.5774 |
1.1547 |
31 |
0.5150 |
0.8572 |
0.6009 |
1.1666 |
32 |
0.5200 |
0.8480 |
0.6249 |
1.1792 |
33 |
0.5446 |
0.8387 |
0.6494 |
1.1924 |
34 |
0.5592 |
0.8290 |
0.6745 |
1.2062 |
35 |
0.5736 |
0.8192 |
0.7002 |
1.2208 |
36 |
0.5878 |
0.8090 |
0.7265 |
1.2361 |
37 |
0.6018 |
0.7936 |
0.7536 |
1.2521 |
38 |
0.6157 |
0.7880 |
0.7613 |
1.2690 |
39 |
0.6293 |
0.7771 |
0.8098 |
1.2867 |
40 |
0.6428 |
0.7660 |
0.8391 |
1.3054 |
41 |
0.6561 |
0.7547 |
0.8693 |
1.3230 |
42 |
0.6691 |
0.7431 |
0.9004 |
1.3456 |
43 |
0.6820 |
0.7314 |
0.9325 |
1.3673 |
44 |
0.6947 |
0.7193 |
0.9657 |
1.3902 |
45 |
0.7071 |
0.7071 |
1.0000 |
1.4142 |
405 |
68 |
0.9272 |
0.3746 |
2.4751 |
2.6695 |
69 |
0.9330 |
0.3586 |
2.0051 |
2.7904 |
70 |
0.9397 |
0.3420 |
2.7475 |
2.9238 |
71 |
0.9455 |
0.3256 |
2.9042 |
3.0715 |
72 |
0.9511 |
0.3090 |
3.0777 |
3.2361 |
73 |
0.9563 |
0.2024 |
3.2709 |
3.4203 |
74 |
0.9613 |
0.2756 |
3.4874 |
3.6279 |
75 |
0.9650 |
0.2588 |
3.7321 |
3.8637 |
76 |
0.9703 |
0.2419 |
4.0108 |
4.1336 |
77 |
0.9744 |
0.2250 |
4.3315 |
4.4454 |
78 |
0.9781 |
0.2079 |
4.7046 |
4.9007 |
79 |
0.9816 |
0.1908 |
5.1446 |
5.2406 |
80 |
0.9848 |
0.1736 |
5.6713 |
5.7588 |
81 |
0.9877 |
0.1564 |
6.3128 |
6.3924 |
82 |
0.9903 |
0.1392 |
7.1154 |
7.1853 |
83 |
0.9925 |
0.12187 |
8.1443 |
8.2055 |
84 |
0.9945 |
0.10453 |
9.5668 |
— |
85 |
0.9962 |
0.08716 |
11.4301 |
11.474 |
86 |
0.9976 |
0.06976 |
14.3007 |
14.335 |
87 |
0.9986 |
0.05384 |
10.0811 |
19.107 |
88 |
0.9954 |
0.03490 |
28.6363 |
28.654 |
89 |
0.9903 |
0.01745 |
57.2900 |
57.299 |
90 |
1.0000 |
Inf. |
Inf. |
Inf. |
Reduced. Moreover, the joint compound forms a seal inside the screwed joint, which prevents leakage and ensures a tight joint.
Joint compounds are commercially available, or they may be made on the job from a variety of different materials. Red lead, white lead, or graphite have frequently been used as a joint compound. Red lead produces a very tight joint, but it hardens to such an extent that it is difficult to unscrew the joint for repairs.
A tape material has also been developed for use in making up screwed joints. It functions in the same manner as a joint compound. The tape is made of Teflon and is so thin that it will sink into the threads when wrapped around them.
An old toothbrush is an excellent tool for applying joint compound to the thread. It is important to remember that the joint compound must be applied to the male thread only. If it is applied to the female thread, some of it will be forced into the pipe where it will lodge as a contaminating substance.
The numerous wrenches used in pipe fitting may be listed as follows:
Monkey wrench
Pipe wrench
• Stillson wrench
• Chain wrench Strap wrench
Open wrench
The important point to remember in pipe fitting is to select a suitable wrench for the job at hand. Each of the aforementioned wrenches is designed for one or more specific tasks. No wrench is suitable for every task encountered in pipe fitting.
A monkey wrench has smooth parallel jaws that are especially adapted for hexagonal valves and fittings (see Figure 8-12). Not only does it fit better on the part to be turned, it also does not have the crushing effect of a pipe wrench.
The operating principle of a pipe wrench is simple. The harder you pull, the tighter it squeezes the pipe. The pipe wrench was designed for use on pipe and screw fittings only. On parallel-sided objects, its efficiency is not up to that of a monkey wrench, and its squeezing action can do a great deal of damage.
Many inexperienced fitters have learned from experience that using a pipe wrench too large for the job can cause the fitting to
Figure 8-12 Using a monkey,-Lk wrench.
&
Stretch or crack. The result is a leaking joint that will require a new fitting to remedy the damage.
A Stillson wrench has serrated teeth jaws that enable it to grip a pipe or round surface in order to turn it against considerable resistance. The correct method for using a Stillson wrench is illustrated in Figure 8-13. Adjust the wrench so that the jaws will take hold of the pipe at about the middle part of the jaws. To support the wrench and prevent unnecessary lost motion when the wrench engages the pipe, hold the jaw at A, with the left hand pressing it against the pipe. At the beginning of the turning stroke B, with the jaw held firmly against the pipe with the left hand, the wrench will at once bite or take hold of the pipe with only the lost motion necessary to bring jaw C in contact with the pipe.
Figure 8-14 shows a chain wrench (or pipe tongs) and the method in which it is used. Although they are made for small sizes up, they are generally used for 6-inch pipe and larger.
A strap wrench (see Figure 8-15) is used when working with plated or polished-finish piping in order not to mar the surface. It also comes in handy in tight places where you cannot insert a Stillson wrench.
Open-end wrenches (see Figure 8-16) are used for making up flange couplings. The right size should be used in order to prevent wearing of the bolt heads or slippage that can cause bruised knuckles.
|
JAWS ON ■BITE’ Figure 8-13 Method of using a Stillson wrench. |
Figure 8-14 Method of using a chain wrench. |
|
Either a pipe vise or a machinist vise (see Figure 8-17) can be used in pipe fitting. The pipe vise is used for pipe only. The machinist vise, on the other hand, has square jaws or a combination of square and gripper jaws, making it suitable for pipe as well as other work.
Several precautions should be taken when using a pipe vise. It exerts a powerful force at the jaws, which in some cases can do damage to the pipe. That is why experienced fitters never put a valve or fitting into a vise when making up a joint at the bench. There is too much danger of distorting the part by oversqueezing it or of putting the working parts of a valve out of line. The correct and incorrect methods of connecting a valve to a pipe are illustrated in Figure 8-18. Always hold a valve between lead — or copper-covered machinist vise jaws while unscrewing the bonnet (see Figure 8-18).
|
■SOFT’ JAW COVERS OF LEAD OR COPPER |
Figure 8-18 Correct method of using the pipe and machinist vise.
Pipe fitting may be defined as the operations that must be performed in installing a pipe system made up of pipe and fittings. These pipe fitting operations can be listed as follows:
1. Cutting.
2. Threading.
3. Reaming.
4. Cleaning.
5. Tapping.
6. Bending.
7. Assembling.
8. Making up.
Figure 8-19 illustrates the principal operations in pipe fitting. After being marked to length by nicking with a file, the pipe is put in a vise and cut with a pipe cutter (or hacksaw) as shown in Figure 8-19A. Any external enlargement is removed with a metal file (see Figure 8-19B). The thread is next cut with stock and dies as in Figure 8-19C. After carefully cleaning the thread with a hard toothbrush and applying red lead or pipe cement to the freshly cut thread, the joint is made up with a Stillson wrench (see Figure 8-19D).
Pipe is manufactured in different lengths varying from 12 to 22 feet. Accordingly, it must be cut to required length for the pipe
Figure 8-19 Pipe cutting. |
(B) |
Installation. This may be done with either a hacksaw or a pipe cutter. The latter method is generally quicker and more convenient.
When a length of pipe is being cut or threaded, it is held firmly in a pipe vise. The pipe vise should be adjusted just tight enough to prevent the pipe from slipping, but not so tight as to cause the jaw teeth to unduly dig into the pipe.
A pipe cutter is a tool usually consisting of a hoop-shaped frame on whose stem a slide can be moved by a screw. On the side and frame, several cutting dies on wheels are mounted. In cutting, the
pipe cutter is placed around the pipe so that the wheels contact the pipe. The tool is rotated around the pipe, tightening up with the screw stem each revolution until the pipe is cut.
The operating principles of a three-wheel cutter and a combined wheel and roller cutter are illustrated in Figure 8-20A. The cuts show the comparative movements necessary with the two types of cutters to perform their functions. The three-wheel cutter requires only a small arc of movement and is recommended for cutting pipe in inaccessible locations. The wheel cutter has a greater range than the roller cutter and is therefore preferred for general use.
The major disadvantage of a pipe cutter is that it does not cut but crushes the metal of the pipe, leaving a shoulder on the outside and a burr on the inside. This does not apply to the knife-type pipe cutter designed to actually cut (not crush) the pipe.
Figure 8-20B shows the appearance of pipe when cut by a hacksaw or knife cutter and when cut by a wheel pipe cutter. When the latter is used, the external enlargement must be removed by a file and the internal burr by a pipe reamer.
A pipe thread is cut with stock and dies. Adjustable dies are used in pipe threading because of slight variations in fittings, especially cast — iron fittings. Figure 8-21 illustrates an adjustable pipe stock and dies for double-ended dies. As shown, each pair of dies has one size thread at one end and another size at the other end. Thus, the two dies in the stock are in position for cutting ^-inch thread, and by reversing them they will cut %-inch thread. The cut shows plainly the reference marks, which must register with each other in adjusting the dies by means of the end setscrews to standard size.
A vise is used in conjunction with the pipe stock and dies when threading a pipe. After securing the pipe in the vise, use plenty of oil in starting and cutting the thread. In starting, press the dies firmly against the pipe until they take hold. After a few turns, blow out the chips and apply more oil. This should be done several times before completing the cut. When complete, blow out the chips as cleanly as possible and back off the dies. When drawing in your breath preliminary to blowing out the chips, turn your head away from the die to avoid drawing the chips into your lungs.
A nipple is short piece of pipe 12 inches in length or less and threaded at both ends. Nipples are properly cut by using a nipple holder designed for use with hand stock and dies. The holder is double ended and holds two sizes of nipples, one being for ^-inch nipples and the other for 3/4-inch nipples. In construction, there is a
|
|
|
|
|
|
|
|
|
|
METAL UPSET BY CRUSHING ACTION OF PIPE CUTTER WHEEL |
……………………. ‘ |
Figure 8-20 The appearance of a pipe cut by a hacksaw and a pipe cut by a cutter wheel. |
Pin inside the holder having a fluted end that digs into the nipple end when pressed forward by driving down the wedge. In operation, the nipple is screwed by hand into the holder as far as it will go, and then the wedge is driven down sufficiently to firmly secure the nipple. The holder is arranged in such a way that when the thread is cut, the nipple can be removed by simply starting back the wedge, which loosens the inner part of the holder and allows the nipple to be easily unscrewed by hand. The holder can be used for making either right or both right and left nipples.
The burrs should be removed with a reamer to avoid future trouble with clogged pipes. This is a job that should be done thoroughly.
The correct way of removing the shoulder (that is, external enlargement) left on a pipe end after cutting it with a pipe cutter is by using a flat file. Obviously at each stroke, the file should be given a turning motion, removing the excess metal through an arc of the circumference. The position of the pipe is changed in the vise from time to time until the excess metal is removed all around the pipe. When the operation is done by moving the file in a straight line, it will result in a series of flat places on the surface. A good pipe threader will also remove the external enlargement of the pipe end caused by using a pipe cutter.
Dirt, sand, metal chips, and other foreign matter should be removed from pipelines to prevent future problems. When a new pipeline is installed, flush it out completely with water to remove any loose scale or foreign matter.
Check the threads for any dirt or other foreign matter. It is important to be thorough about this because dirt in the threads can also get into the lines when the joints are made up. Dirt can also cause tearing of the metal when screwing up a connection. It increases friction and interferes with making a tight joint.
Flanged faces should also be cleaned thoroughly. Manufacturers usually coat flanges with a heavy oil or grease to prevent rusting. A solvent will easily remove this coating. Special precaution should be taken against dirt on gaskets. Dirt on any part of a flanged joint tends to cause leaks.
An internal or female thread is cut by means of a pipe tap, a conical screw made of hardened steel and grooved longitudinally. A pipe tap and pipe reamer are illustrated in Figure 8-22.
Table 8-20 gives drill sizes that permit direct tapping without reaming the holes beforehand. Table 8-21 gives drill sizes for both the Briggs, or American Standard, and the Whitworth, or British Standard.
Figure 8-22 A typical pipe tap and pipe reamer. |
With the proper tools, pipes may be bent within certain limits without difficulty.
An example of a pipe-bending tool is illustrated in Figure 8-23.
Pipes can also be bent by hand without the use of special tools. One method involves the complete filling of the pipe with sand and capping both ends so that none of the sand will be lost. Heat the part to be bent and then clamp the pipe in a vise as close to the part to be bent as possible. Now cool the outside with water so that the inside, being hot and plastic, is compressed as the bend is made.
Figure 8-23 Pipe-bending tool.
Assembling is the operation of putting together the various lengths of pipe and fittings used in an installation.
If no mistakes have been made in cutting the pipe to the right length or in following the dimensions on the blueprint, the pipe and fittings may be installed without difficulty. In other words, the last joint (either a right or left union, or long screw joint) will come together smoothly or, as they say in the trade, make up.
Table 8-20 Drill Sizes for Briggs Standard Pipe Taps (For Direct Tapping Without Reaming)
416 |
Size of V8 !4 3/a 3/4 1 11/4 11-2 2 2V2 3 31/2 4
Pipe
Size of 21/64 7/16 9/16 45/64 29/32 19/64 131/64 14%4 213/«4 25/8 3V4 34%4 415/64
Drill
Table 8-21 Drill Sizes for Pipe Taps
|
Screwed joints are put together with red or white lead pigment mixed with graphite and linseed oil, or with some standard commercial joint compound.
It is unnecessary to put much material on the threads because it will be simply pushed out and wasted when the joint is screwed up.
It should be put on evenly and cover all the threads, with care being taken not to let any touch the reamed end of the pipe where it may get inside. The red lead is preferably obtained in the powder form and mixed with oil and a little dryer at the time the pipe is to be made up. Get a clean piece of glass on which to prepare the lead. The toothbrush should be laid on the glass after applying the lead in order to avoid getting grit on the brush and paint on the table. When grit becomes mixed with the lead, it prevents close contact of the filling and pipe, thus making the joint less efficient.
The following steps should be taken before making up a screwed joint:
1. Ream the pipe ends.
2. Remove burrs from both the inside and outside of the pipe.
3. Thoroughly clean the inside of the pipe.
4. Thoroughly clean the threads.
Clean threads, a suitable joint compound, and proper tightening (neither too much nor too little) are all necessary for a satisfactory screwed joint.
There are four requirements for satisfactorily making up a flanged joint. In the proper order of sequence, these four requirements are as follows:
Thorough cleaning Accurate alignment
• Using the proper gasket
Tightening bolts in proper order
Thoroughly clean the flange face with a solvent to remove any grease, and wipe it dry. The alignment must be accurate for satisfactory makeup. This is particularly important where valve flanges are involved. If the alignment is poor, a severe stress on the valve flanges may distort the valve seats and prevent tight closure (see Figure 8-24).
Selecting a suitable gasket for the service is also very important. Using the wrong gasket may result in a leak.
Figure 8-25 illustrates the recommended method of tightening the bolts with a wrench. This must be done not in rotation but in sequence as indicated by the numbers. This is the crossover method. Do not fully tighten on the first round but go over them two or preferably three times to fully tighten.
|
Figure 8-24 Flange and pipe alignment.
|
Nonferrous Pipes, Tubing, and Fittings
Both brass and copper are used as materials for this type of pipe and tubing. The construction may be either cast or wrought, and the methods of joining include screwed, flared, and soldered.
The technique used with screwed fittings is the same as with ordinary malleable-iron fittings. This has already been described in the first part of this chapter.
The fittings used for flared soft tube end joints are cast fittings. These are usually used on oil burner construction and supply lines. Flared joint fittings include elbows, tees, couplings, unions, and a full range of reducing and adapter combinations in all standard sizes and combinations of sizes from 1/8 inch to 2 inches inclusive (see Figure 8-26). A double-seal type of flared joint fitting is illustrated in Figure 8-27.
The sequence of operations required to make a flared joint are as follows:
1. Cut the tube with a hacksaw to the exact length, using a guide to ensure a square cut.
2. Remove all burrs and irregularities by filing both inside and outside.
3. Slip the coupling nut over the end of the tube and insert the flanging tool.
4. Drive the flanging tool into the tube with a few hammer blows, expanding the tube to its proper flare.
5. Assemble the fitting and tighten it by using two wrenches, one on the nut and the other on the body of the fitting.
Solder fittings usually come in cast bronze and wrought copper. The two kinds of fittings used are the edge-feed fitting and the hole — feed fitting (see Figure 8-28).
The basic principle of solder fittings is capillary attraction. Because of capillary attraction, solder can be fed vertically upward between two closely fitted tubes to a height many times the distance required to made a soldered joint, regardless of the size of the fitting.
Either a 50-50 tin-lead solder or a 95-5 tin-antimony solder is recommended for joining copper tube. The former is generally used for moderate pressures with temperatures ranging up to 250°F. The 95-5 tin-antimony solder is used where higher strength is required, but it has the disadvantage of being difficult to handle. Pressure ratings for soldered joints using these two solders are listed in Table 8-22. A suitable paste-type flux is recommended for use with these solders.
®®> @7
T FITTING UNION 90°ELBOW
MALE ADAPTER FEMALE ADAPTER FLARING TOOL
|
FEMALE ADAPTER RIGID PIPE |
Figure 8-27 Double-seal flared joint fitting. |
Figure 8-28 Edge — and hole-feed solder fittings.
Table 8-22 Safe Strength of Soldered Joints Pressure Ratings, Maximum Service Pressure (psi)
*Standard copper water tube sizes +ASTM B32, alloy grade 50A *Including refrigerants and other noncorrosive liquids and gases §ASTM B260, brazing filler metal (Courtesy Copper & Brass Research Assoc.) |
The series of operations necessary in making a solder fitting joint are as follows:
1. Measure the tube to proper length so that it will run the full length of the socket of the fitting.
2. Cut the tube end squarely.
3. Clean tube end and socket of fitting.
4. Apply soldering flux to the cleaned areas of tube and fitting socket.
5. Assemble the joint.
6. Revolve the fitting if you can, to spread the flux evenly.
7. Apply heat and solder.
8. Remove residual solder and flux.
9. Allow joint to cool.
With a hole-feed fitting that has a feed hole for the solder and a groove inside, the procedure is just the same as for an edge-feed fitting except that solder is fed into the feed hole until it appears as a ring at the edge of the fitting. Be sure the hole is kept full of solder, as it shrinks on cooling and solidifying.
Do not select fittings that are oversize because they will result in a loose fit. The capillary action is dependent on a fairly tight fit, although a certain amount of looseness can be tolerated. A loose fit causes the greatest difficulty when working with large-size copper tubes.
A thorough cleaning of the tube surface and the fitting socket is absolutely essential for a strong, tight, and durable joint. This cannot be emphasized too strongly.
Brazing is rapidly taking the place of many operations formerly performed by soldering because it is simpler and quicker and results in a stronger joint. Like soldering, the brazing alloy is applied at temperatures below the melting point of the metal being brazed. In this respect, both brazing and soldering differ from welding, which forms a joint by melting (fusing) the metal at temperatures above its melting point.
During the brazing process, the brazing alloy is heated until it adheres to the pipe surface and enters into the porous structure of the metal. The brazed joint is almost always as strong as the brazed metal surrounding it.
Brazing can be used to join nonferrous metals, such as copper, brass, or aluminum, or ferrous metals, such as cast iron, malleable iron, or steel. The brazing alloy used in making the joint depends on the type of metal being brazed. For example, aluminum requires the use of a special aluminum brazing alloy, whereas a low-temper — ature brazing alloy or a silver alloy is recommended for brazing copper and copper alloys. A local welding supply dealer should be able to provide answers to your questions about which alloy to use.
The procedure for brazing consists essentially of the following operations:
1. Clean both surfaces.
2. Apply a suitable flux.
3. Align and clamp the parts to be joined.
4. Preheat the surface until the flux becomes fluid.
5. Apply a suitable brazing alloy.
6. Allow the surface time to cool.
7. Clean the surface.
The pipe surfaces must be thoroughly cleaned, or the result will be a weak bond or no bond at all. All dirt, grease, oil, and other surface contaminants must be removed, or the capillary attraction so important to the brazing process will not function properly.
Select a flux suited to the requirements of the brazing operation. Fluxes differ in their chemical compositions and the brazing temperature ranges within which they are designed to operate. Apply the flux to the joint surface with a brush.
Align the parts to be joined, securing them in position until after the brazing alloy has solidified. Preheat the metal to the required brazing temperature (indicated by the flux reaching the fluid stage).
After the flux has become fluid, add the brazing alloy. If conditions are right, the brazing alloy will spread over the metal surface and into the joint by capillary attraction. Do not overheat the surface. Remove the heat as soon as the entire surface has been covered by the brazing alloy. Allow time for the joint to cool and then clean the surface.
Braze welding is another bonding process that does not melt the base metal. In this respect, it resembles both soldering and brazing.
Brazing and braze welding operate under essentially the same basic principles. For example, both use nonferrous filler metals that melt above 880°F but below the melting point of the base metal. They differ primarily in application and procedure.
The braze-welding process follows most of the steps previously described for brazing but will differ principally as follows:
1. Edge preparation is necessary in braze welding and is essentially similar to that employed in gas welding. The edges must be prepared before the surfaces are cleaned.
2. A suitable filler metal is used instead of a brazing alloy.
The filler metal will flow throughout the joint by capillary attraction. Flanges that are to be brazed to copper pipes must be of copper or what is known as brazing metal (98 percent copper and 2 percent tin), as gunmetal flange would melt before the brazing alloy ran.
Oxyacetylene welding (gas welding) is probably the most common welding process used for joining pipe and fittings, particularly on smaller installations. Arc welding is also very popular.
Pipe welding should be done only by a skilled and experienced worker. The equipment and the procedure used are much more complicated than those used with soldering, brazing, or braze welding.
Welding forms a joint by melting (fusing) the metal at temperatures above its melting point. The filler metal, electrodes, or welding rods used must be suitable for use with the base metal to be welded, and the procedure used should be such as to ensure complete penetration and thorough fusion of the deposited metal with the base metal. The welding process is employed in many piping installations, but especially those in which large-diameter pipes are used.
Manufactured steel welding fittings are available for almost every conceivable type of pipe connection. These steel welding fittings can be divided into the following two principal categories:
Butt-welding fittings
• Socket-welding fittings
Butt-welding fittings (see Table 8-23) have ends that are cut square or beveled 371/2° for wall thicknesses under 3/i6 inch. Wall thicknesses ranging from 3/i6 inch to 3/4 inch are beveled 37V20. For walls ranging from 3/4 inch to 13/4 inches thick, the bevel is U — shaped.
Socket-welding fittings (see Table 8-24) have a machined recess or socket for inserting the pipe. A fillet weld is made between the pipe wall and the socket end of the fitting. The fillet weld is approximately triangular in cross-section, the throat lying in a plane of approximately 45° with respect to the surfaces of the part joined. As shown in Figure 8-29, the minimum thickness of the socket wall (L) is 1.25 times the nominal pipe thickness (T) for the designated schedule number of the pipe. Socket-welding fittings are generally limited in use to nominal pipe sizes 3 inches and smaller.
In addition to butt- and socket-welding fittings, flange fittings are also available for welding in sizes ranging from inch to 24 inches.
L L(minimum) = 1.25 T Figure 8-29 Filletweld
BUT NOT LESS THAN 5/3 |
|
M |
427 |
Nominal Pipe Size |
Long Radius Elbows |
ISO Returns |
Straight Tees |
||||||
Outside Diameter at Bevel |
Center to End |
||||||||
Outside Diameter at Bevel |
Center to Center O |
Back to Face K |
Outside Diameter at Bevel |
Center to End |
|||||
900 Elbows A |
45° Elbows B |
||||||||
Run C |
Outlet M |
||||||||
1 |
1.315 |
1У2 |
78 |
1.315 |
3 |
2У16 |
1.315 |
1У2 |
1% |
1У4 |
1.660 |
17/8 |
1 |
1.660 |
33/4 |
23/4 |
1.660 |
17/8 |
17/8 |
1У2 |
1.900 |
21/4 |
1У8 |
1.900 |
41/2 |
31/4 |
1.900 |
21/4 |
21/4 |
2 |
2.375 |
3 |
13/8 |
2.375 |
6 |
43l6 |
2.375 |
21/2 |
21/2 |
2У2 |
2.875 |
33/4 |
13/4 |
2.875 |
71/2 |
5З16 |
2.875 |
3 |
3 |
3 |
3.500 |
4У2 |
2 |
3.500 |
9 |
61/4 |
3.500 |
33/8 |
33/8 |
3У2 |
4.000 |
51/4 |
21/4 |
4.000 |
101/2 |
71/4 |
4.000 |
334 |
33/4 |
4 |
4.500 |
Б |
2У |
4.500 |
12 |
81/4 |
4.500 |
41/8 |
41/8 |
5 |
5.563 |
7У2 |
31/8 |
5.563 |
15 |
105/16 |
5.563 |
4% |
47/8 |
Б |
6.625 |
9 |
33/4 |
6.625 |
18 |
125/16 |
6.625 |
55/8 |
55/8 |
8 |
8.625 |
12 |
5 |
8.625 |
24 |
165/16 |
8.625 |
7 |
7 |
10 |
10.750 |
15 |
61/4 |
10.750 |
30 |
203/8 |
10.750 |
81/2 |
81/2 |
12 |
12.750 |
18 |
7У2 |
12.750 |
36 |
243/8 |
12.750 |
10 |
10 |
14 |
14.000 |
21 |
83/4 |
14.000 |
42 |
28 |
14.000 |
11 |
|
16 |
16.000 |
24 |
10 |
16.000 |
48 |
32 |
16.000 |
12 |
Not |
Standard |
|||||||||
18 |
18.000 |
27 |
111/4 |
18.000 |
54 |
36 |
18.000 |
13Ь |
|
20 |
20.000 |
30 |
121/2 |
20.000 |
60 |
40 |
20.000 |
15 |
|
24 |
24.000 |
36 |
15 |
24.000 |
72 |
48 |
24.000 |
17 |
From American Standard for Butt-Welding Fittings, ASA BI6.9-l958.All dimensions are in inches. Dimension A is equal to V2 of dimension O. (Courtesy I960ASHPAE Guide) |
428 |
Center to Bottom of Socket |
Socket Wall Thickness, Min |
Bore Diameter of Fitting |
||||||||
Sched 40 |
Sched |
Sched |
Sched |
Sched |
Sched |
Sched |
Sched |
|||
Depth of |
And 80 |
160 |
Bore Diameter |
40 |
80 |
160 |
40 |
80 |
160 |
|
Nominal |
Socket, |
Of Socket, Min |
||||||||
Pipe Size |
Min |
A |
B |
C |
D |
|||||
Vs |
3/8 |
7/i6 |
— |
0.420 |
0.125 |
0.125 |
— |
0.269 |
0.215 |
— |
X/4 |
3/8 |
7/i6 |
— |
0.555 |
0.125 |
0.149 |
— |
0.364 |
0.302 |
— |
3/s |
3/8 |
1732 |
— |
0.690 |
0.125 |
0.158 |
— |
0.493 |
0.423 |
— |
V2 |
3/8 |
5/8 |
34 |
0.855 |
0.136 |
0.184 |
0.234 |
0.622 |
0.546 |
0.466 |
3/4 |
1/2 |
3/4 |
% |
1.065 |
0.141 |
0.193 |
0.273 |
0.824 |
0.742 |
0.614 |
1/2 |
12 |
7/s |
11/16 |
1.330 |
0.166 |
0.224 |
0.313 |
1.049 |
0.957 |
0.815 |
L!/4 |
V2 |
11/16 |
1V2 |
1.675 |
0.175 |
0.239 |
0.313 |
1.380 |
1.278 |
1.160 |
1V2 |
V2 |
1V4 |
11/2 |
1.915 |
0.181 |
0.250 |
0.351 |
1.610 |
1.500 |
1.338 |
2 |
5/8 |
11/2 |
15/8 |
2.406 |
0.193 |
0.273 |
0.429 |
2.067 |
1.939 |
1.689 |
2V2 |
5/8 |
21/4 |
2.906 |
0.254 |
0.345 |
0.469 |
2.469 |
2.323 |
2.125 |
|
3 |
5/8 |
21/4 |
21/2 |
3.535 |
0.270 |
0.375 |
0.546 |
3.068 |
2.900 |
2.626 |
(Courtesy I960ASHRAE Guide) |
The gas pipe installations in which gas-fired furnaces, boilers, heaters, or other gas appliances are used deserve special attention because of the volatile and highly flammable nature of the fuel. Special attention should be given to the installation of gas piping to ensure against leakage.
The installation and replacement of gas piping should be done only by qualified workers who have the necessary skills and experience.
The following recommendations are offered as a guide for installing and replacing gas piping:
All work should be done in accordance with the building, heating, and plumbing codes and standards of the authorities having local jurisdiction. These take precedence over national codes and standards.
In an existing installation, the gas supply to the premises and all burners in the system must be shut off before work begins. When installing a system, size the pipes according to the amount of gas to be delivered to each outlet and at the proper pressure. The length of pipe runs and number of outlets are the main determining factors.
Use a piping material recommended by the local authorities having jurisdiction. Never bend gas piping because it may cause the pipe walls to crack and leak gas. Use fittings for making turns in gas piping. Take all branch connections from the top or side of horizontal pipes (never from the bottom).
• Locate the gas meter as close as possible to the point at which the gas service enters the structure.
Make certain all pipes are adequately supported so that no unnecessary stress is placed on them.
• Offsets should be 45° elbows rather than 90° fittings in order to reduce the friction to the flow of gas.
• Check for gas leaks by applying a soap-and-water solution to the suspected area. Never use matches, candles, or any other flame to locate the leak.
Insulating the supply pipes in a low-pressure steam or hot-water space heating system will reduce unwanted heat loss and improve the heating efficiency of the system. The return pipes in a hot-water heating system should also be insulated so that the water reaches the boiler with a minimum of heat loss. Do not insulate the return pipes in a steam heating system. Uninsulated pipes will aid in the condensation of any steam that has succeeded in bypassing the thermostatic traps and entering the returns.
The pipe insulation material must be noncombustible, durable, and resistant to moisture. Furthermore, it should be able to retain its original physical shape and insulating properties after becoming wet and drying out.
Fiberglass is used to insulate steam or hot-water heating pipes. It can be easily applied to the pipe, requiring little more than ordinary cutting shears or a sharp knife.
Another effective pipe-insulating material is expanded polystyrene (see Figure 8-30).
Figure S-30 Expanded polystyrene as a pipe-insulating material. (Courtesy Dow Chemical Co.) |
Your local building supply dealer should be able to answer any questions you may have about pipe-insulting materials. The manufacturers of these materials also generally provide detailed instruction about how to apply them. You should not have any difficulty if you carefully read and follow these instructions.
Each piping installation will have design or layout problems that the fitter must solve. Many of these problems, such as installing dirt pockets or siphons, are quite simple for the pipe fitter to handle.
More-complicated layout problems are solved by calculating and installing lift fittings, swivels and offsets, and drips. These and other piping details are described in the sections that follow.
Many steam fitters connect risers directly to mains with a tee; although this method saves on extra labor and expense, it results in a more inefficient operation of the installation. When a tee is used, the condensation falls directly across the path of the steam flowing in the main and will be carried along and finally arrive at the radiator or convector with excess moisture. This problem is avoided with a 45° connection.
Using a 45° connection very effectively drains the condensation from the main, the path of the condensation being along the metal of the pipe and fittings instead of dripping directly into the steam.
The proper method of connecting a riser to a main where the riser has a direct connected drip pipe is by using a 45° connection downward. If the riser has no drip, the riser should be connected to the main with the leadoff being 45° upward connecting with a 45° elbow. The runout should pitch V2 inch per foot. Runouts over 8 feet in length, but with less than 1i2 inch per foot pitch, should be one size larger than specified in the pipe sizing tables.
If the condensation flows in the opposite direction to the steam, the runouts should be one size larger than the vertical pipe and pitched Vi inch per foot toward the main. If the runouts are over 8 feet in length, use a pipe two sizes larger than specified.
Connections to Radiators or Convectors
The connections to radiators and convectors must have a proper pitch when installed and be arranged so that the pitch will be maintained under the strains of expansion and contraction. These connections are made by swing joints.
In two-pipe systems, radiators are connected either at the top and bottom opposite end or at the bottom and bottom opposite end. The top connection is not recommended for best performance. Short radiation may be top-supply and bottom-return connected on the same end.
Additional information about radiator and convector connections can be found in Chapter 2 of Volume 3 (“Radiators, Convectors, and Unit Heaters”).
The lift fittings illustrated in Figure 8-31 are adapted for use on the main return lines of vacuum heating systems at points where it is desired to raise the condensation to a higher level. In operation, the
NOTE: Cold-water line connected to opposite side. Place gate valve & check valve in this connection. Figure 8-31 Typical installation of lift fittings. |
Momentum of the water is maintained and assists in making the lift with minimum loss of vacuum. The lift fitting is constructed with a pocket at the bottom of the lift into which the water drains. As soon as sufficient water accumulates to seal this pocket, it is drawn to the upper portion of the return by the vacuum produced by the pump. The shape of the fitting is such that dirt and scale are usually swept along by the current. Cleanout plugs are provided for use if necessary. A second fitting in a reversed position is recommended for use at the top of the lift to prevent water from running back while the pocket is filled.
A steam main in any steam heating system may be dropped to a lower level without dripping if the pitch is downward with the direction of the steam flow. By the same token, the steam main in any system may be elevated if properly dripped.
Various piping arrangements for dripping the main and riser are illustrated in Figures 8-32 through 8-39. Figure 8-39 shows a connection where the steam main is raised and the drain is to a wet return. If the elevation of the low point is above a dry return, it may be drained through a trap to the dry return in a two-pipe vapor, vacuum, or subatmospheric system.
Figure 8-32 Dripping end of main into wet return.
TRAP |
SUPPLY MAIN Figure 8-33 Dripping end of main into dry return. |
A horizontal steam main can be run over an obstruction if a small pipe is carried below for the condensation with provisions for draining it.
In vacuum steam heating systems, drip traps for steam mains should be either thermostatic or combination float and thermostatic protected by dirt strainer or dirt pockets. Typical methods of making these connections are illustrated in Figures 8-40 through 8-43. The bases of supply risers are dripped through drip traps as
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Shown in Figures 8-44 and 8-45. Methods of connecting return risers are also shown.
In vapor steam heating systems, runouts to supply risers should be dripped separately into a wet return.
On all systems employing thermostatic traps, dirt pockets should be located so as to protect the traps from scale and muck, which will interfere with their operation. Dirt pockets are usually made 8 to 12 inches deep.
A siphon (see Figure 8-46) is used to prevent water from leaving the boiler due to lower pressure in a dry return. Condensation from the drip pipe falls into the loop formed by the siphon and, after it is filled, overflows into the dry pipe. The water will rise to different heights (G and H in the legs of the siphon) to balance the difference in pressure at these points.
If a dry return is used without a siphon, then water would be drawn from the boiler in sufficient amounts to balance the low pressure in the riser, filling the return and drip to approximately point M (see Figure 8-46).
Another method employed to prevent water leaving the boiler is the Hartford connection (or loop) on the wet return (see Chapter 15 of Volume 1, “Boilers and Boiler Fittings”).
In putting together lengths and return bends to form a coil heating unit, there is a right way and a wrong way to do the job. The essential requirement for the satisfactory operation of the coil is providing
Figure 8-35 Method of dripping short steam main and discharging condensation into pressure wet return near floor. |
For proper drainage. To obtain this, the pipes should not be parallel but should have a degree of pitch.
A pitch fitting should be used to obtain pitch in the coils rather than the so-called drunken thread method (see Figure 8-47). The drunken thread is obtained by removing the guide bushing from the stock and cutting the thread out of alignment. This gives a
poor joint—one that will eventually break because of corrosion. The corrosion is caused by the deep cut on one side of the pipe resulting from cutting the thread out of alignment.
Figure 8-36 Method of dripping long steam main and discharging condensation into pressure wet return near floor. |
Long runs of rigidly supported piping carrying steam or hot water, especially when they are at high pressures and temperatures, are
UP TO RADIATOR RETURN TRAP Figure 8-37 Alternative method of dripping end of supply main through dirt pocket to pressure wet return near floor and venting to overhead dry return. |
Figure 8-38 Method of dripping base of main supply riser of downfeed system through dirt strainer and drip trap. |
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Figure 8-40 Method of dripping steam mains with drips on end of main. |
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DOWNFEED SUPPLY RISER TO RADIATOR Figure 8-42 Method of installing drip connection at base of downfeed supply riser to overhead return main through cooling leg, dirt strainer, and return trap. |
DOWNFEED SUPPLY RISER Figure 8-43 Method of installing drip connection at base of downfeed supply riser to overhead return main. |
Often subject to stresses caused by the expansion and contraction of the pipe. These pipe stresses can be relieved in a number of ways, including the installation of either a U-expansion bend or an expansion joint.
Another method of providing for pipe expansion in steam mains is through the use of swivels and offsets (see Figure 8-48). Allow at least 4 feet of offset for each inch of expansion to be taken up in the line. The offsets should be placed far enough apart to minimize any strain on the threads when expansion or contraction occurs.
RISER RISER RISER riser Figure 8-44 Method of connecting drips from upfeed risers into a wet return and discharging some through a trap into overhead vacuum return main. |
Water pockets (that is, the tendency for water to collect in pipes) are caused by incorrect pipe installation methods (see Figures 8-49 and 8-50). Not only do these water pockets have the potential danger of freezing and damaging the pipes when the boiler is shut down, but they also cause that loud and disagreeable hammering in the pipes known as water hammer. Water hammer is caused by a sudden rush of steam picking up this undrained water when the radiator or convector is opened and forcing it against any turn in the direction of the main. Hammering in steam lines can be stopped by providing for the proper drainage of the condensation. This can be accomplished by installing eccentric fittings or by installing traps of suitable capacity. For example, the water pocket shown in Figure 8-50 can be avoided by using an eccentric reducing tee (see Figure 8-51).
Water trapped in a supply line can sometimes be the cause of radiators failing to heat properly. In this case, the trapped water is
Figure 8-45 Method of connecting drips from downfeed risers into wet return and discharging some through a trap into overhead vacuum return main. |
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Figure 8-47 Right and wrong ways of making up coils. |
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Usually caused by an improperly pitched supply line, rather than fittings. You can create a slight pitch in the line by slipping wedges under the radiator. Space the wedges so that the radiator remains level (check it with a carpenter’s level); otherwise, the radiator will not operate properly.
ECCENTRIC REDUCING FITTING |
Figure 8-51 Using an eccentric reducing fitting to eliminate water pockets. |
Pressure tests are performed on hydronic heating systems on a periodic basis to determine the condition of the piping/tubing and system components. These tests are described in Chapter 1 (“Radiant Heating Systems”) in Volume 3.