Valves and Valve Installation

A valve is a device used for controlling the flow or pressure of a fluid in the pipes of steam and hot-water heating systems. Valves are generally restricted in use to the control function for which they were designed. Specifically, a valve may be used to control a fluid in one of the following ways:

Stopping its flow

• Checking its flow

• Throttling its flow

• Diverting its flow

• Reducing its temperature

• Relieving its pressure Reducing or regulating its pressure

Valve Components and Terminology

The operation of a valve may be controlled either internally or externally, depending on the type of valve. For example, the opera­tion of a check valve depends on the fluid flow in the pipe. Because the operation of this type of valve is controlled internally and is therefore automatic in nature, no means are provided for external adjustment. Access to the working parts (disc, seat rings, ball, and so on) of a check valve is usually obtained through a cap secured to the valve bolt by bolts or a threaded connection. The operation of most other types of valves is controlled externally, either manually or automatically.

Generally speaking, an externally controlled valve consists of a body to which an extension (a bonnet, yoke, or yoke and bonnet) is attached. The bonnet contains the valve stem, packing nut, and stuffing box. The yoke consists of upright arms mounted on the bonnet or on a gasket placed on the neck of the valve body. When a yoke is used, the stem is threaded and guided through the upper yoke arm.

The valve stem is an adjustable screw or shaft inside the bonnet that opens or closes the valve by moving a disc holder and disc attached to the end of the stem up or down inside the valve body

(see Figure 9-1). The valve closes when the disc makes full contact with the valve seat, a stationary surface in the valve body. The valve opens when the stem pulls the disc holder and disc up off the valve seat. Some valves use a wedge or plug to vary the flow of the medium through the valve by varying the size of the opening

One method of classifying these externally controlled valves is according to the design of the bonnet. The following are four com­mon valve bonnet designs:

Valves and Valve Installation

Union bonnet Screwed bonnet Bolted flanged bonnet Bolted flanged yoke bonnet

A union bonnet (see Figure 9-2A) is secured to the valve body by a heavy ring nut. A bevel on the bottom of the bonnet engages with a corresponding bevel in the body neck. The ring nut fits down over the bonnet, covering the body neck and the bottom portion of the bonnet. A tight seal can be obtained by wrenching down the ring nut. The joint is additionally sealed by the pressure from within the valve body.

The advantage of a union bonnet is that its construction provides a quick and easy method of coupling and uncoupling the bonnet and valve body.

Valves and Valve Installation

Figure 9-2A Union bonnet. (Courtesy Wm. Powell Co.)

A screwed bonnet (see Figure 9-2B) is secured to the valve body by a threaded connection. There are two basic types of screwed bon­nets. One type has threads on the outside of the base of the bonnet and on the inside of the body neck and is sometimes referred to as a screwed-in bonnet. The other type has threads on the inside of the bonnet and on the outside of the body neck. It is referred to as a screwed-on bonnet.

A bolted flanged bonnet (see Figure 9-2C) is attached to the top of the valve body neck by bolts. The joint formed by the connection between these two surfaces may be one of the following three types:

Valves and Valve Installation

Figure 9-2B Screwed bonnet. (Courtesy Wm. Powell Co.)

Valves and Valve Installation

Figure 9-2C Bolted flanged bonnet. (Courtesy Wm. Powell Co.)

(1) flat-faced joint, (2) male and female joint, or (3) tongue-and — groove joint. Each of these joints is illustrated in Figure 9-2D.

A flat-faced joint is generally used only in low-pressure service. The possibility of a gasket blowing out is eliminated when a male and female joint is used because it provides correct gasket compres­sion and ensures alignment between the bonnet and the valve body. A tongue-and-groove joint is used in high-pressure and high-tem — perature installations. Its construction also ensures perfect align­ment of the bonnet onto the valve body.

Some valves may also be classified according to the type of valve stem used with the bonnet valves, which sometimes includes screwed and union bonnet types. The stems used with these valves include the following:

Valves and Valve Installation

Figure 9-2D Bolted flanged bonnet. (Courtesy Wm. Powell Co.)

• Outside screw, rising stem with bonnet.

• Inside screw, rising stem with bonnet.

• Inside screw, nonrising stem with bonnet.

• Outside screw, rising stem with yoke.

The stem is the shaft connecting the handwheel at the top of the valve to a wedge or disc in the valve body. The handwheel turns the stem, which changes the position of the wedge or disc and opens or closes the valve.

An outside screw stem (see Figure 9-3) is one that has the threaded portion of the stem shaft outside the valve. The advantage of this stem is that the threads do not come in contact with the

Valves and Valve InstallationFigure 9-3 Rising and nonrising

Stem valves. (Courtesy Wm. Powell Co.)

Media inside the valve and thereby avoid the possibility of erosion and corrosion. If the stem threads are located inside the valve, it is called an inside screw stem.

A stem may also be referred to as a rising or nonrising stem. A rising stem is a stem shaft that moves upward as the valve hand­wheel is turned in a counterclockwise direction (that is, to the open position). A nonrising stem does not rise but merely turns with the handwheel. The stem rotates in the bonnet or yoke and is threaded into a disc holder, which is threaded into the wedge or disc. Nonrising stem valves are especially suited where clearance is limited.

Valves and Valve InstallationA wedge (see Figure 9-4) is a device used to control the flow of steam or water through a gate valve. When the valve is wide open, the wedge is lifted entirely out of the main chamber of the valve body, providing a straight­way flow area through the valve.

Wedges for gate valves are available in the following types: (1) split wedge,

(2) solid wedge, (3) double wedge, and (4) flexible wedge. These wedges are illustrated in Figure 9-5.

Figure 9-4 Sectional view of a split wedge.

(Courtesy Wm. Powell Co.)

подпись: figure 9-4 sectional view of a split wedge.
(courtesy wm. powell co.)
The wedge is attached to the end of the valve stem. When the valve is closed, the wedge is in full contact with the seat.

In globe, angle Y globe and angle, and check valves, a disc is used to con­trol the flow of the steam or water. A disc is a flat device attached to the end of the valve stem. The exception to the rule is the swing­check valve, which has no stem. In this valve, the position of the disc is controlled internally by the flow of the steam or water. In operation, the disc opens or closes the pathway through the valve depending on the position of the stem. Some different types of discs and seats are illustrated in Figure 9-6.

Both composition and metal discs are used in valves. The com­position discs are suitable for service other than high tempera­ture. While they do not last as long as metal discs on throttling service, they will enable the seat to last longer by taking most of the wear of wire drawing. They are also easier and cheaper to replace.

Metal discs last longer than composition discs on throttling ser­vice and on higher-temperature service. So-called plug-type discs are suitable for close throttling service.

Valves and Valve Installation

Figure 9-5 Wedges for gate valves. (Courtesy Wm. Powell Co.)

The wedge or disc closes tightly against a seat to close off the valve. As illustrated in Figure 9-7, the valves and seats may be either flat or beveled. For equal discharge capacity, a beveled valve must be opened more than a flat valve.

Valve Materials

Valves are made of a number of different metals and metal alloys, and the choice of metal often will mean the difference between good or bad service. This is a very important point to remember, because it is not simply a matter of going down to the local supply house with only the valve design and function in mind. You must also consider the service for which the valve is intended. Regardless of the type of valve you select, it should be rated for its pressure and service temperature range. You would not want to select valves rated for 125 psi saturated steam and a steam service temperature range to 500F maximum if your system is capable of producing pressures and temperatures in excess of these limits.

The standards and specifications prescribing the rules and regu­lations for valve construction and use will be found in the latest publications of the following associations:

• American Petroleum Institute (API Specifications)

• American National Standards Institute (ANSI Codes and Standards)

INTEGRAL SEAT

Valves and Valve Installation

RENEWABLE SEAT

Valves and Valve Installation

SEMI-CONE PLUG EQUAL PERCENTAGELINEAR FLOW PLUG V PORT PLUG

PLUG

For On-Off Service

подпись: for on-off service

For fine non­characteristic flow regulation.

PLUG For equal percentage flow characteristic for pre-determined valve performance. Equal increments of valve lift give equal percentage increases in flow.

For linear flow characteristic regulation with high pressure drops.

For linear flow characteristic regulation with medium and low pressure drops.

Figure 9-6

Y valves.

подпись: figure 9-6
y valves.
Examples of discs and seats provided for globe, angle, and

• American Society of Mechanical Engineers (ASME Boiler Construction and Unfired Pressure Vessel Code)

• American Society for Testing Materials (ASTM Material Specifications)

• Manufacturers ’ Standardization Society of the V alve and Fittings Industry (MSS Standard Practices)

Valves and Valve Installation

Valves are available in the following metals and metal alloys:

• Bronzes

• Cast iron

• Semisteel

• Stainless steel

• Low-carbon and low-alloy steel

• Special alloys and pure metals

Bronze valves are suitable for steam pressures of 125 psi and 150 psi at 500F and 200 psi, 300 psi, and 350 psi at 550F. For steam pressures of 125 psi and 250 psi at 450F, cast-iron valves are rec­ommended. Steel valves should be used for higher pressures and temperatures. Valves made of pure metals and metal alloys are used in processing systems where resistance to the corrosive and erosive action of the fluids is of prime consideration.

Information About Valves

Valve manufacturers are especially willing to help you select the most suitable valve for your needs. They produce excellent informative liter­ature to this end, including illustrations, specifications, and installation and operating procedures for their valves. This information is available by downloading it from their Web sites or by writing them directly.

• Wm. Powell Co.

2503 Spring Grove Avenue Cincinnati, Ohio 45214 513-852-2000 Www. powellvalves. com

• Spirax Sarco Inc.

Northpoint Business Park 1150 Northpoint Blvd.

Blythewood, South Carolina 29016

803-714-2000

Www. spiraxsarco-usa. com

Honeywell, Inc.

101 Columbia Road Morristown, New Jersey 07962 973-455-2000

Www. honeywell. com (continues)

• Hoffman Specialty

3500 N. Spaulding Avenue Chicago, Illinois 60618 773-267-1600 Www. hoffmanspecialty. com

• Bell & Gossett

8200 N. Austin Avenue Morton Grove, Illinois 60053 847-966-3700 Www. bellgossett. com

Watts Industries Inc.

815 Chestnut Street

North Andover, Massachusetts 01845

978-688-1811

Www. wattsind. com

Globe and Angle Valves

Globe and angle valves are used primarily as throttling devices to control the rate of flow. Flow characteristics of both globe and angle valves are illustrated in Figure 9-8.

Valves and Valve Installation

A globe valve is a valve that has a round ball-like shell with a stuffing box extension through which passes the screw spindle, which operates the valve disc. The valve seat is parallel to the line of flow, and the inlet and outlet branches are opposite one another.

The design and construction of an angle valve is similar to the globe valve, except that the outlet is at right angles to the inlet branch, thus combining in itself a valve and an elbow.

Globe and angle valves are preferred to gate valves (see following section) if the valve is to be operated frequently or if it is to be used as a throttling device (that is, operated partially open), because either type can open with fewer turns. An additional feature of the angle valve is that it can control both a change and the direction of flow. It is designed to create a 90° change in direction. As a result, it saves an elbow and nipple and reduces the pressure loss.

Globe valves are commonly used in pipelines that extend through basement areas or areas of limited access. Offset globe valves are often recommended for radiators on second floors or higher. Angle valves are commonly used on first-floor radiators.

Ordinarily, globe and angle valves should be installed with the pressure under the disc so that the stuffing box may be repacked without escape of steam or water. Installing these valves in this manner not only promotes easier operation but also provides a cer­tain degree of protection to the packing and reduces the erosive action on the disc and seat faces. High-temperature steam service proves to be the exception. If high-temperature steam is the medium to be controlled, the globe or angle valve should be installed so that the pressure is above the valve disc. If the usual installation method (that is, with the pressure under the disc) is used, then the high-tem — perature steam will be under the disc when the valve is closed, and the valve stem will be out of the fluid. As a result, the valve stem will cool and contract, causing the disc to lift slightly off the valve seat. The leaks that then occur result in wire drawing on seat and disc faces.

Figure 9-9 illustrates both the correct and incorrect way to place globe valves on horizontal lines. When the globe valve is placed in an upright position, considerable water will remain in the pipeline and be subject to freezing. When it is placed in a horizontal posi­tion, most of this water will drain through the seat opening with less danger of damage by freezing.

Figures 9-10, 9-11, and 9-12 illustrate a number of commonly used globe and angle valves. These illustrations should be referred to when reading the section on troubleshooting valves.

Valves and Valve Installation

WRONG WAY

SEAT OPENING HORIZONTAL

RIGHT WAY

подпись: seat opening horizontal
 
right way
Figure 9-9 Correct and incorrect way of placing a globe valve on a horizontal line.

Gate Valves

A gate valve (see Figure 9-13) is one having two inclined seats between which the valve (consisting of a single or double disc) wedges down in closing. In opening, the valve is drawn up into a dome or recess, thus leaving a straight passage the full inside diam­eter of the pipe. This lifting of the wedges completely out of the waterway, thereby creating an unobstructed passage for the fluid, is a significant feature of the gate valve. As a result, turbulence is min­imized, and there is very little pressure drop.

Gate valves are the most frequently used valves and are prefer­able to globe or angle valves for lines on which it is important to minimize resistance to flow and friction losses. They are also neces­sary where complete drainage of the pipe must be provided.

The gate valve is primarily suited for locations where valves are to be generally wide open or shut tight. Globe valves are preferable for throttling. When gate valves are used for throttling, the high velocity of flow tends to damage the surface of the seats.

Wedge gate valves are preferable where the valve is to be installed with the stem extending downward. Nonrising stem gate valves are usually tighter at the stuffing box than those with rising stems and require less headroom.

The double-disc gate valve enjoys certain advantages over the single-disc type (see Figure 9-14). If the fluid contains foreign mat­ter, the flexibility of operation of the double disc enables one disc to

Valves and Valve Installation

F

подпись: f

1. PACKING NUT

2. PACKING GLAND

3. PACKING

4. BONNET RING

5. SEAT RING

6. HANDWHEEL NUT

7. IDENTIFICATION PLATE

8. HANDWHEEL

A. SCREWED-IN BONNET

B. UNION BONNET

C. HI-LO DISC

1C-DISC HOLDER 2C-NON-METALLIC DISC 3C-DISC PLATE 4C-DISC NUT

COMPOSITION DISC 1E-DISC HOLDER 2E-NON-METALLIC DISC 3E-DISC-LOCKNUT WASHER DISC LOCKNUT 1F-DISC NUT 2F-DISC

G. STEM-DISC LOCKNUT (HORSE SHOE RING ) TYPE

2G-HORSE SHOE RING

H. STEM-NEEDLE DISC TYPE

L. BODY-GLOBE-FLANGED ENDS M. BODY-GLOBE-SOLDER JOINT ENDS N. BODY-ANGLE-THREADED ENDS

Figure 9-10 Screwed and union bonnet globe and angle valve.

(Courtesy Wm. Powell Co.)

Seat tightly if dirt or some other type of foreign matter is present. Moreover, the discs and seats are more readily refaced than those of the single-disc type.

Outside screw and yoke valves should be used when it is necessary to know at a glance whether the valve is open or shut tight.

Some examples of gate valves used in heating and cooling instal­lations are illustrated in Figures 9-15, 9-16, and 9-17. Refer to

Valves and Valve Installation

1.

HANDWHEEL-ROUND

16.

COMPOSITION DISC HOLDER

2.

PACKING NUT

17.

NON-METALLIC DISC

3.

PACKING GLAND

18.

DISC LOCKNUT

4.

PACKING

19.

SLIP-ON DISC

5.

BODY NUT

20.

STEM-NEEDLE DISC TYPE

6.

BODY STUD

21.

HI-LO DISC LOCKNUT

7.

BONNER

22.

DISC HOLDER

8.

GASKET

23.

NON-METALLIC DISC

9.

BODY-GLOBE-FLANGED ENDS

24.

DISC PLATE

10

SEAT RING

25.

DISC NUT

11

BODY-GLOBE-THREADED ENDS

26.

BODY-ANGLE-FLANGED ENDS

12

HANDWEEL NUT

27.

STEM-DISC LOCKNUT TYPE

13

IDENTIFICATION PLATE

28.

DISC LOCKNUT

14

HAND WHEEL-NON-HEATING

29.

DISC

15

STEM-SLIP-ON DISC TYPE

Figure 9-11 Bolted bonnet inside screw globe and angle valve.

(Courtesy Wm. Powell Co.)

These illustrations when reading the section on troubleshooting valves in this chapter.

Gate valves are available with either a rising or nonrising stem, the former being more commonly used on smaller gate valves.

Check Valves

A check valve is one that automatically opens to permit the passage of liquid in one direction and automatically closes to prevent any flow in the opposite direction. In other words, it specifically operates to prevent the reversal of water flow in the line.

Valves and Valve Installation

1.

HANDWHEEL (ROUND)

16.

STEM-SLIP-ON TYPE

2.

PACKING GLAND

17.

DISC-ONE-PIECE-SLIP-ON

3.

PACKING

18.

COMPOSITION DISC HOLDER

4.

GLAND STUD NUT

19.

COMPOSITION DISC

5.

GLAND STUD

20.

DISC NUT

6.

YOKE STUD NUT

21.

DISC LOCKNUT

7.

YOKE STUD

22.

DISC

8.

GASKET

23.

DISC LOCKNUT-HI-LO DISC

9.

BODY-GLOBE-FLANGED ENDS

24.

DISC HOLDER

10

SEAT RING

25.

NON-METALLIC DISC

11

BODY-GLOBE-THREADED ENDS

26.

DISC PLATE

12

STEM-DISC LOCKNUT TYPE

27.

DISC NUT

13

HANDWHEEL NUT

28.

BODY-ANGLE-FLANGED ENDS

14

IDENTIFICATION PLATE

29.

YOKE

15

HANDWHEEL

Figure 9-12 Bolted bonnet outside screw and yoke globe and angle

Valve. {Courtesy V&n. Powell Co.)

A check valve is sometimes placed on the return connection to prevent the accidental loss of boiler water to the returns with con­sequent danger of boiler damage. When feasible, the Hartford con­nection is preferred over the check valve because the latter is apt to stick or not close tightly. Moreover, the check valve offers additional

Resistance to the condensation returning to the boiler, which in gravity systems would raise the water line in the far end of the wet return several inches.

Figure 9-13 Gate valve flow characteristics.

(‘Courtesy Wm. Powell Co.)

подпись: 
figure 9-13 gate valve flow characteristics.
('courtesy wm. powell co.)
The two general types of check valves are (1) the swing-check valve and (2) the lift­check valve. A third type sometimes used is the ball-check valve.

Swing-check valves (see Figure 9-18A) operate best on horizontal lines. If they are to be used on vertical or inclined lines, they should be installed so that the flow will be upward through the valve. When the valve disc is raised in the open position, there is very little obstruction in the flow area. Turbulence is also very low. Swing-check valves are commonly used in combination with gate valves.

Lift-check valves (also referred to as hori — zontal-lift check valves) (see Figure 9-18B) have the same flow characteristics as a globe valve. This can be seen by comparing the illus­trations. The turbulence and pressure drop are

Valves and Valve Installation

Valves and Valve Installation

1.

HANDWHEEL NUT

D.

SCREWED-IN BONNET-NON RISING STEEM

2.

IDENTIFICATION PLATE

VALVES

3.

HANDWHEEL

E.

UNION BONNET — NON-RISING STEM VALVES

4.

PACKING GLAND

F

UNION BONNET-RISING STEM VALVES

5.

PACKING BOX SPUD

G.

BONNET RING

(NON-RISING STEM VALVES ONLY)

H.

SOLID WEDGE-NON-RISING STEM VALVES

6.

PACKING

J.

SOLID WEDGE — RISING STEM VALES

7.

PACKING NUT

K.

DOUBLE WEDGE-RISING STEM VALVES

A.

STEM-NON RISING STEM VALVES

L.

SEAT RING

B.

STEM — RISING STEM VALVES

M

BODY-FLANGED ENDS

C.

SCREWED-IN BONNET-RISING STEM

N.

BODY-THREADED ENDS

VALVES

O.

BODY-SOLDER JOINT ENDS

Figure 9-15 Screwed and union bonnet rising and nonrising stem gate

Valve. (Courtesy Wm. Powell Co.)

Therefore similar for these two valves. Lift-check valves are com­monly used in combination with globe valves.

A vertical check valve should be used on vertical lines only and with the flow upward through the valve.

The Watts Backflow Preventer is a safety device containing two check valves and is designed to prevent backflow in boiler feed lines when the supply pressure falls below system pressure. The primary check valve in the backflow device utilizes a disc that seats against a rubber mating part to ensure tight closing. A secondary check valve utilizes a disc-to-metal seating. If the downstream check valve malfunctions (for example, fouls), leakage will be vented to

(SHD

,6

Valves and Valve Installation

(SkO

подпись: (sko Valves and Valve Installation Valves and Valve Installation

HANDWHEEL NUT HANDWHEEL BONNET BODY NUTS GASKET BODY BOLTS BODY SEAT RING GLAND NUTS

подпись: 
handwheel nut handwheel bonnet body nuts gasket body bolts body seat ring gland nuts

I-—(18:;

подпись: i-—(18:; Valves and Valve InstallationPACKING GLAND

PACKING

SPUD

GLAND BOLTS STEM

WEDGE NUT SET SCREW WEDGE NUT WEDGE WEDGE

SHAPE \* MERGEFORMAT Valves and Valve Installation

Figure 9-16 Bolted bonnet inside screw nonrising stem gate valve.

(Courtesy Wm. Powell Co.)

Atmosphere through the vent port, thereby safeguarding the potable water from contamination.

Figures 9-19 through 9-23 illustrate a number of different check valves used in heating and cooling installations. Refer to these illustrations when reading the section on troubleshooting valves in this chapter.

Valves and Valve Installation

1. STEM BUSHING NUT

15. BODY STUD AND NUTS

2. HANDWHEEL

16. SPLIT WEDGE

3. LUBRICANT FITTING

17. SOLID WEDGE

4. YOKEARMS

18. PACKING GLAND

5. YOKEARM EAR BOLT AND NUT

19. PACKING

6. BONNET BOLT AND NUT

20. PACKING WASHER

7. TWO-PIECE BONNET

21. EYEBOLT NUT

8. BODY-FLANGED ENDS

22. EYEBOLT

9. BEARING CAP

23. ONE-PIECE BONNET

10. HANDWHEEL KEY

24. PACK-UNDER-PRESSURE BUSHING

11. STEM BUSHING

25. GASKET

12. BEARING CAP BOLT

26. BODY-WELDED ENDS

13. BEARING CAP NUT

27. SEAT RING

14. STEM

Ure 9-17 Bolted bonnet outside

>crew and yoke rising stem gate

Valve. (Courtesy Wm. Powell Co.)

Stop Valves

Globe, gate, and angle valves are used on steam and hot — or cold — water pipelines as stop valves (also referred to as nonreturn valves, nonreturn stop valves, or boiler check valves).

Valves and Valve Installation

(A) (B)

Figure 9-18 Flow characteristics of a swing — and lift-check valve. (Courtesy

Wm. Powell Co.’)

The operating principle of the typical stop valve is shown in Figure 9-24. It functions as a form of check valve that can be opened or closed by hand control when the pressure in the boiler is greater than in the line, but it cannot be opened when the pressure within the boiler is less than that in the line. The counterbalance spring slightly overbalances the weight of the valve and tends to hold the valve open, thus preventing movement of the valve with every fluctuation of pressure.

8.

BODY-FLANGED END

9.

BODY-THREADED END

10. DISC LOCKNUT-COMPOSITION DISC

11.

DISC HOLDER

12. COMPOSITION DISC

A.

DETAIL-ONE SIDE PLUG

B.

DETAIL-TWO SIDE PLUGS

 

1. CAP

2. SLIDE PLUG

3. CARRIER PIN

4. CARRIER

5. DISC NUT

6. DISC

7. BUMPER PLUG

 

Valves and Valve Installation

Valves and Valve Installation

1

CAP

2

DISC

12

RING NUT

3

BODY-THREADED ENDS

13

DISC GUIDE

4

CAP

14

DISC

5

BALL

15

BODY-THREADED ENDS

6

BODY-THREADED ENDS

16

RING NUT

7

RING NUT

17

DISC GUIDE

8

DISC GUIDE

18

DISC HOLDER

9

DISC

19

DISC-COMPOSITION DISC

10

SEAT RING

20

DISC NUT

11

BODY-THREADED ENDS

21

BODY-THREADED ENDS

Figure 9-20 Screwed-cap horizontal-lift check valve. (Courtesy Wm. Powell Co.)

Stop valves are often used as a safety device in steam power plants where more than one boiler is connected to the same header. They are connected directly to the boiler nozzle outlet between the boiler and the header. They function as a safety device to prevent backflow of the steam into the boiler. This is particularly important if the boiler is cold.

The stop valve should be installed so that the valve stem is in a vertical or upright position. The pressure of the steam or water should be under the disc.

Butterfly Valves

A butterfly valve consists of a round (cylindrical) body, a shaft (stem), and a disc that rotates on the shaft (see Figure 9-25). The

Valves and Valve Installation

11.

BODY-FLANGED ENDS

12.

DISC HOLDER HANGER

13.

PIPE PLUG

14.

DISC HOLDER’

15.

DISC NUT

16.

DISC NUT PIN

17.

SEAT RING

A.

DETAIL—HANGER TYPE DISC

B.

DETAIL—PIN TYPE-TWO SIDE PLUGS

C.

DETAIL—PIN TYPE-ONE SIDE PLUG

1.

BODY NUT

2.

BODY STUD

3.

CAP SCREW

4.

LOCKWASHER

5.

BODY BOLT

6.

BODY BOLT NUT

7.

DISC HOLDER PIN

8.

CAP

9.

GASKET

10

DISC

подпись: 1. body nut
2. body stud
3. cap screw
4. lockwasher
5. body bolt
6. body bolt nut
7. disc holder pin
8. cap
9. gasket
10 disc
Figure 9-21 Bolted-cap swing-check valve. (Courtesy Wm. Powell Co.)

Disc rotates 90 degrees from its open to closed positions. The valve disc provides tight shutoff, although a smaller disc size is available that does not provide tight shutoff.

A butterfly valve is used to control the flow of hot water or water from a condenser in two-position or proportional applications. These valves are available as two-way units. A three-way configuration can be achieved by connecting two two-way butterfly valves to a pipe tee.

Butterfly valves may be operated manually or by a unidirectional or reversing electrically operated actuator (see Figure 9-26). They

Valves and Valve Installation

1

CAP—BOLTED

9. CAP BOLT NUT

2

SPRING (OPTIONAL)

10. COMPOSITION DISC HOLDER

3

DISC HOLDER

11. NON-METALLIC DISC

4

TEFLON DISC

12. DISC GUIDE

5

DISC GUIDE

13. METAL DISC

6

GASKET

14. BODY—THREADED ENDS

7

BODY-FLANGED ENDS

15. BODY—SILVER BRAZE ENDS

8

CAP BOLT

16. BODY—SOLDER JOINT ENDS

Figure 9-22 Bolted-cap horizontal-lift check valve. (Courtesy Wm. Powell Co.)

Are available in sizes ranging from 2 to 12 inches and in either wafer or lug body designs.

Two-Way Valves

A two-way valve is a valve with only one inlet port and one outlet port. This category of valves is used to provide tight shutoff in straight and angled hydronic and steam piping systems. Two-way valves are designed to control the medium (water or steam) in either two-way or proportional applications. All two-way valves

Valves and Valve Installation

1.TOP BODY—FLANGED ENDS

2. BALL

3. BOTTOM BODY—FLANGED ENDS

4. DISC HOLDER

5. COMPOSITION DISC

6. DISC NUT

7. TOP BODY—THREADED ENDS

8. DISC

9. BOTTOM BODY—THREADED ENDS

Figure 9-23 Vertical check valve. (Courtesy Wm. Powell Co.)

Valves and Valve Installation

Figure 9-24 Functions of a stop or nonreturn valve.

Provide tight shutoff in their closed position. Linear, quick-opening, and equal-percentage-flow two-way valves are available. The type selected will depend on the control requirements of the medium. For example, a linear valve is used for the proportional control of steam or chilled water, or for the control of a medium in applications that do not have wide load variations. A quick-opening two-way valve is used for the two-position control of steam. An equal — percentage two-way valve is used for the proportional control of hot water in hydronic systems.

Three-Way Valves

Three-way valves are globe valves with three ports used in either mixing or diverting applications. When used for mixing (for exam­ple, as a water-tempering valve), the valve uses two inlet ports and one outlet port (see Figure 9-27). If the three-way valve functions as a diverting valve, it has one inlet port and two outlet ports.

The three-way or cross valve shown in Figure 9-28 functions as a diverting valve. It is used to control the flow of the medium to or from a branch line at the junction of a branch and main line. It is essentially a globe valve with its seat located at the bottom of the body and the passage through the seat connected with a third open­ing at right angles to the other two openings.

Y Valves

A Y valve or Yglobe valve (see Figure 9-29) is designed to combine the operating characteristics of globe and gate valves. In other words, it combines the throttling characteristics of the former with the straightway flow area of the latter. The valve disc can be easily reground and renewed.

Valve Selection

Valves are available in a wide range of designs, sizes, pressure capac­ity ranges, materials, operating characteristics, and other factors criti­cal to specific applications. The valves must have adequate capacity to support the heating and cooling loads. At the same time, they must be able to efficiently control the flow of water or steam in the system.

The following factors must be taken into consideration when selecting valves for a heating/cooling system:

• Type of medium (water or steam) being controlled

• Pressure and temperature ranges of the medium

• Piping arrangement Piping size

The valve manufacturer publishes a specification sheet for each of its valves, which includes the following information:

Valve size

• Operating pressure

STANDARD HANDLE

Valves and Valve Installation

5" and up—2 pins

Figure 9-25 Exploded view of a butterfly valve. (Courtesy Watts Industries, Inc.)

• Maximum and minimum temperature range

• Reduced pressure range

• Valve material

• Valve capacity

The maximum and minimum temperature range of the valve must match the maximum and minimum temperature of the medium (water or steam) being controlled. The maximum pressure of the medium must never exceed the maximum pressure rating of the valve. If the medium is potentially corrosive (for example, chlo­rinated water), the valve components must be made of a corrosion — resistant material.

The full open and closed pressure drop across the valve is also an important consideration. The pressure drop is the measured differ­ence in upstream and downstream pressures of the medium flowing through the valve. The flow of the fluid through the valve increases as the pressure drop increases until it reaches a critical point. This point is called the critical pressure drop and is the point at which increases of the pressure drop no longer increase the flow rate of

Valves and Valve Installation

Figure 9-26 Butterfly valve with electrically operated actuator. (Courtesy Honeywell, Inc.)

The medium. Instead, it is dissipated as noise and vibration. The vibration can eventually destroy the valve and adjacent pipe fittings if allowed to continue.

The pressure drop of the valve in its full open position must not exceed the valve rating for quiet operation and normal service life. On the other hand, the full open pressure drop must be high enough to enable the valve to operate efficiently. Finally, the closed pressure drop of a valve must not exceed its close-off rating and, if used, that of its operator (actuator).

Valves are available with screwed (threaded) ends or flanged ends. The piping size (diameter) will determine the valve end selec­tion. Larger-diameter pipes require bolted flange ends.

Still another consideration in valve selection is whether the valve is normally closed or open when at rest. This will depend on a number of factors, including the type of load being controlled, the medium (water or steam) being controlled, the system configuration, and

WALTS NO. 6 WALTS 100XL

Valves and Valve Installation

The valve application. For example, converter control valves should be normally closed, whereas outdoor preheat valves should be nor­mally open.

Troubleshooting Valves

Valve manufacturers generally provide information for servicing and repairing their valves. When the information is not available, as is often the case on older heating and cooling systems, troubleshooting the valve problem generally depends on experience or educated guesswork. Experience has shown that most valve problems can be traced to one of the following three sources:

Valves and Valve Installation

• Stuffing-box leakage

• Seat leakage

• Damaged stem

Valve Stuffing-Box Leakage

Leakage around the valve stuffing box is usually an indication that the stuffing must be adjusted or replaced. This leakage does not occur when the valve is completely opened or closed. Therefore, an absence of leakage is not necessarily an indication that the valve is functioning normally.

Once you have detected leakage, check first to determine whether or not adjusting the packing will stop it. If it is a bolted bonnet valve, turn the packing gland nuts (or gland stud nuts) clockwise alternately with no more than Vi turn on each until leakage stops. If you are dealing with a screwed and union bonnet valve, turn the packing nut clockwise until the leakage stops. If the leakage will not respond to adjustment, the packing must be replaced.

The procedure for replacing the packing in most valves may be summarized as follows:

1. Remove the handwheel nut and the handwheel.

2. Remove the packing nut.

3. Slip the packing gland off of the stem.

4. Replace the packing.

5. Reassemble in reverse order.

The procedure used with bolted bonnet outside screw and yoke valves is a little more complicated. On Y valves of this type, it is necessary to remove the gland flange and gland follower before replacing the packing. On globe and angle valves, the stud nuts and upper valve assembly must be removed.

Because of their design and construction, the problem of stuffing — box leakage does not occur with check valves.

Valve Seat Leakage

Leakage of water from the valve body is usually an indication that the wedge, disc, or seat ring needs replacing. For most valves, the procedure for doing this may be summarized as follows:

1. Open the valve.

2. Remove the bonnet and other components of the upper valve assembly.

3. Run the stem down by turning it in a clockwise direction.

4. Remove the wedge or disc from the stem and replace if necessary.

5. Remove the seat ring with a seat ring wrench and replace if necessary.

6. Reassemble in reverse order.

The disc, disc assembly, and ball are all possible sources of seat leakage in check valves. Access to these components is gained by removing the valve cap (counterclockwise), side plugs, and pins. Reassembly is in reverse order.

Damaged Valve Stems

Sometimes the threads on valve stems become worn or damaged, making the valves inoperable. When this occurs, the stems must be replaced. Before the stem can be replaced, however, all pressure must be removed. Then, with pressure removed, disconnect and remove the bonnet and upper valve assembly. The remainder of the procedure depends on the type of stem used (that is, rising or nonrising stem) and other design factors. Basically, the procedure may be summarized as follows:

1. Run the stem down by turning it in a clockwise direction.

2. Rotate the stem in a clockwise direction until the stem threads are completely out of the threaded portion of the upper bushing.

3. Pull the stem out of the stuffing box.

4. Remove the wedge or disc from the stem.

5. Replace the old stem with a new one.

6. Reassemble in reverse order with new packing and gasket (when applicable).

Automatic Valves and Valve Operators

An automatic valve is a controlled device designed to regulate the flow of steam, water, gas, or oil in response to impulses from a con­troller such as a thermostat. The controller measures changes in the surrounding variable conditions (for example, temperature, humid­ity, and pressure) and activates the valve in order to compensate for these changes. The controller, controlled device, and a feedback

Device constitute a closed-loop automatic control system. A more

Detailed description of the operating principles of an automatic control system is contained in Chapter 4 (Thermostats and Humidistats)’.

A number of different automatic valves are used in heating and cooling systems. They are generally available in two-way or three­way models and can be used for either two-position or modulating operation or both. The type of automatic valves used must be care­fully sized and selected for the specific application. Valve manufac­turers generally provide information to aid you in making a suitable selection.

When selecting an automatic valve, do not confuse the valve body rating with the close-off rating. The former is the actual rating of the valve body, whereas the latter indicates the maximum allow­able pressure drop to which the valve may be subjected while fully closed. The close-off rating is a function of the power available from the valve actuator for holding the valve closed against pres­sure drop (although structural parts such as the valve stem are also sometimes the limiting factor).

A valve operator (also called an actuator) is a device designed to automatically operate a valve. The operator (actuator) may be an integral part of the valve, or the valve and operator may be two separate devices. It receives the electrical, electronic, or pneumatic impulses from the controller and activates the valve stem. There are three types of valve operators:

• Solenoid operators

• Pneumatic operators

• Motorized operators

A solenoid operator is commonly used with a valve designed for two-position operation (that is, fully opened or fully closed). It con­sists essentially of a magnetic coil, which electrically operates a mov­able plunger. The plunger controls the opening and closing of the valve. In design, a solenoid-operated valve is less complicated than either the pneumatic or motorized types, but it is limited in size.

The operating principle of a pneumatic operator is based on changes in air pressure. Essentially, it consists of a spring-equipped flexible bellows or diaphragm attached to the valve stem. When the air pressure increases, the bellows or diaphragm moves the stem and compresses the spring. A reduction in air pressure results in the operation reversing itself with the spring returning the valve stem to its original position. Pneumatic-operated valves are designed for proportional control of a medium and are available as normally open or normally closed valves.

Springless pneumatic operators are available with opposing flex­ible diaphragms located on either side of a single diaphragm. This type of pneumatic operator is limited in use to special applications (for example, those involving high pressures or large valves).

A motorized operator consists of an electric motor that operates the valve stem through a gear train and linkage. Based on their operating principles, electric motors used in motorized operators can be classified as follows:

• Unidirectional motors Spring-return motors Reversible motors

The reversible motor illustrated in Figure 9-30 contains both a balancing relay and a feedback potentiometer. The balancing relay controls the motor, which turns the motor drive shaft connected to the gear train.

The balancing relay consists of two solenoid coils with parallel axes, into which are inserted the legs on the U-shaped armature. The armature is pivoted at the center so that it can be tilted by the changing magnetic flux of the two coils to energize the relay. A con­tact arm is fastened to the armature so that it may touch either of the two stationary contacts as the armature moves back and forth on its pivot. When the relay is balanced, the contact arm floats between the two contacts, touching neither of them. In operation, the motor is started, stopped, and reversed by the single-pole double­throw contacts of the balancing relay.

The feedback potentiometer contained in the motor consists of a coil of wire and a sliding contact. It is similar in construction to the internal view of the Honeywell Q181A auxiliary potentiome­ter illustrated in Figure 9-31. In operation, the motor shaft moves the sliding contact of the potentiometer along the coil, establish­ing contact wherever it touches according to the position of the motor.

Motorized valves are commonly used in residential zoning appli­cations. Examples of valves used for this purpose are illustrated in Figures 9-32 and 9-33. Both of these valves contain replaceable O-rings and are equipped with a manual means of opening the valve in case of power failure.

The zone valve shown in Figure 9-32 is available in either line or low-voltage models. The latter requires a 24-volt power source. One advantage of this zone valve is that the powerhead can be replaced without the removal of the valve body from the pipeline.

TRANSFORMER

Valves and Valve Installation

ENDS)

Figure 9-30 A reversible motor with a balancing relay and a

Feedback potentiometer. (Courtesy Honeywell, Inc.)

Caution

Make sure the electrical power is shut off before attempting to install, remove, or repair an electrically operated valve.

Note that the manual opening lever on the powerhead (see Figure 9-32) has two settings: manual open (man. open) and

Valves and Valve Installation

Figure 9-31 Internal view of a Honeywell auxiliary potentiometer.

(Courtesy Honeywell, Inc.)

Automatic (auto). Always place the manual opening lever in the automatic position after the installation procedure has been com­pleted and before running the valve. Always place the manual open­ing lever in the manual position before removing the valve from the pipeline or replacing a powerhead. Never attempt to cycle the valve electrically when the manual opening lever is in this position.

Before attempting to install a new powerhead, drain the water from the system, disconnect the valve from the electrical power source, and remove the conduit connections (if fitted). Then, place the manual opening lever on the old powerhead in the manual position and remove the cover. The remainder of the procedure may be summarized as follows:

1. Take out the four screws connecting the powerhead to the valve body and remove the old powerhead.

2. Replace the old O-ring in the valve body with a new one.

3. Place the manual opening lever on the new powerhead in the manual open position.

Valves and Valve Installation

BODY

Figure 9-32 A Honeywell zone valve. (Courtesy Honeywell, Inc.)

4. Align the powerhead on the valve body in the same position as the old one, and screw it down.

5. Reconnect the conduit and electrical connections.

6. Adjust the thermostat or controller so that the valve runs smoothly through its cycle.

The motorized zoning valve shown in Figure 9-33 is energized by impulses from a standard two-wire thermostat. A wiring diagram for four such valves used in a residential installation is illustrated in Figure 9-34. Low-voltage DC power and circular-burner control is supplied by a unit containing a transformer, a rectifier, and two cir­cuit breakers. When supplied for boilers with self-energizing con­trols, a built-in power failure manual switch is furnished that permits manual boiler operation.

The valve itself contains a water-damped piston that is lifted by a strong magnetic flux and opens a straight-through passage for unre­stricted flow. The valve closes slowly under the action of gravity.

The butterfly valve is ideally suited for regulating the flow of water or steam in applications where tight close-off is not required.

Figure 9-33 An

Valves and Valve Installation

SNAP RING

подпись: snap ringElectro-zone valve.

Valves and Valve Installation

BODY PLUG ASSEMBLY

подпись: body plug assembly

TOP COVER

подпись: top cover Valves and Valve Installation

0 RING

подпись: 0 ring(Courtesy Hydrotherm, Inc.)

Typical applications include zone control of gravity hot-water or low-pressure steam heating systems. For tight close-off, a final shutoff valve must also be used.

The motorized valve illustrated in Figure 9-35 is a single-seated type used for two-position operational control of hot or chilled water, steam radiators, or zoned residential heating and cooling systems. It

Valves and Valve Installation

THERMOSTAT CB-1 ZONE BOX

ELECTROZONE VALVE

!———————————— n

Valves and Valve Installation

, Enclosed circuit

— — is factory wired — -•

On zone paks.

Figure 9-34 Wiring diagram for the zone valve. (Courtesy Hydrotherm, Inc.)

Contains a replaceable composition disc and is designed to operate at fluid temperatures up to a maximum of 250F or steam pressure up to 15 psi maximum.

Automatic room temperature control on hot-water or two — pipe steam heating systems can be accomplished by using self — actuating thermostatic radiator valves (see Figure 9-36). These valves can be used on freestanding radiators, convectors, and baseboard heating units. Electric power is not required for their operation.

CHECK POSITION INDICATOR

MANUAL CONTROL SHAFT

To free rotor, lightly tap motor laminations with screwdriver at point indicated by arrow.

 

OILING

HOLES

 

AUXILIARY CONTROL SWITCH

 

MOTOR

 

Valves and Valve Installation

CONDUIT

OPENING

 

VALVE STEM PIN HOLE

 

SPRING CLIP PACKING NUT TEFLON PACKING

SETSCREW. | ^ ta-Td’"" packing follower

"’".-PACKING SPRING

BONNET

" … ‘ " ‘ . . UNION NUT

STEM /"JI lT /TAIL PIECE

DISC HOLDER " ‘*■” ^ ~ ‘

VALVE DISC

RETAINING NUT VALVE BODY

 

Figure 9-35 Honeywell V5045A valve body and V2045A operator.

(Courtesy Honeywell)

 

Valves and Valve Installation

Valve linkage is used to connect an electric motor to an auto­matic valve. The type of valve linkage used will depend on the type of automatic valve used in the heating or cooling application. The valve manufacturer’s recommendations should be followed to avoid problems.

The valve linkage in Figure 9-37 is an example of the type of link­age used with automatic steam or hot-water valves (see Figure 9-38). Installation and adjustment of this linkage for a two-position valve may be summarized as follows:

1. Follow the manufacturer’s instructions and connect the motor and valve to the linkage. Be sure to align the key on the crank arm with the keyway on the motor shaft.

Valves and Valve Installation

PIPE

SIZE

A

B

C

D

E

V 2

4316

31/2

21/16

13^8

63’16

3z4

43^8

4

2 7/16

19/16

61/2

Figure 9-36 Thermostatic radiator valves showing dimensions of straight-through and angle pattern bodies. (Courtesy Honeywell)

подпись: figure 9-36 thermostatic radiator valves showing dimensions of straight-through and angle pattern bodies. (courtesy honeywell) Valves and Valve Installation Valves and Valve Installation

B

подпись: b

2. The lift adjustment on the valve linkage allows the linkage to be used with a number of valve sizes. Set the lift adjustment equal to the rated lift of the valve according to the three steps illustrated in Figure 9-39.

3. Use the adjusting screw to put tension on the valve in the closed position (see Figure 9-40).

4. Run the motor and valve all the way open. Check to see that the motor runs all the way to the end of the stroke without putting tension on the valve stem. The existence of tension is an indication that it may jam open.

Adjusting the same linkage for a three-way valve involves the same steps, particularly the alignment of the key on the crank arm with the keyway on the motor shaft. The lift adjustment, however, should be set V2 division above the rated valve lift (see Figure 9-39).

With the motor closed and the valve at the bottom of its stroke, loosen the locknut and turn the adjustment screw down until the top of the washer is even with the pointer (see Figure 9-40).

When the motor is run all the way open, the washer at the bot­tom of the strain-relief spring should move upward Vie inch (see Figure 9-41). If it moves more than We inch, reduce the lift adjust­ment. Increase the lift adjustment if it moves less than We inch. Any

Valves and Valve Installation

Figure 9-37 Honeywell model Q601 valve linkage. (Courtesy Honeywell)

Change in the lift adjustment will require that the close-off tension at the bottom of the stroke be reset before continuing. In operation, the motor should be free to run through its entire stroke.

Another type of valve linkage that requires adjustment during its installation is the Honeywell Q455 valve linkage illustrated in Figure 9-42. This linkage is also used with automatic valves in many different types of heating and cooling applications. The method of connecting a Q455 valve linkage to a water or steam valve is illustrated in Figure 9-42. The adjustment procedure for a two-way automatic valve is as follows:

1. Set the lift adjustment on the crank arm to equal the rated lift of the valve (see Figure 9-43).

VALVE SIZE

DIMENSIONS IN INCHES

A

B

C

21/2

91/2

31/2

4y8

3

11

315/16

47/8

4

13

41/2

55/8

5

15

51/2

7%

6

16V 2

61/8

53/8

Valves and Valve Installation

4" MINIMUM CLEARANCE TO REMOVE ACTUATOR

подпись: 4" minimum clearance to remove actuator
 
Figure 9-38 Cage-type single-seated valve used for control of steam,

Liquids, or noncombustible gases. (Courtesy Honeywell)

2. With the motor running closed, turn the adjustment screw down (see Figure 9-43) until the valve is closed and washer A (see Figure 9-44) has been pushed down We inch as indicated on the scale marks.

3. Run the motor all the way open. If the adjustment is correct, the valve will not reach the top of its stroke and jam. A ten­dency to jam will be indicated by tension in the linkage.

The procedure used for connecting a motor and an automatic three-way valve to a Honeywell Q455 valve linkage is identical to that used for the two-way valve. However, there are significant dif­ferences in the adjustment procedure.

The lift adjustment should be set at one mark higher than the rated lift of the automatic valve. Then, with the motor closed, turn the shaft adjustment screw down until the valve is closed and washer A has been pushed down Vie inch. Now, run the motor all the way open and check washer B for a We-inch upward movement (see Figure 9-44).

Valves and Valve Installation

Any readjustment of the lift requires a readjustment of the shaft adjustment screw for proper close-off force on the valve stem at the bottom of the stroke.

An example of a type of valve linkage that does not require adjust­ment during installation is the Honeywell Q618 valve linkage. This valve linkage can be used in most motorized valve applications.

Valve Pipe Connections

The pipe ends or connections of valves are commonly available in the following three types:

Threaded ends

• Flanged ends

• Grooved ends

Threaded-end valves are tapped usually with female threads into which the pipe is threaded. These are the cheapest of the three types to use because less material and finishing are required. On

TURN ADJUSTING LOOSEN

W SCREW DOWN W LOCKNUT

Valves and Valve Installation

Figure 9-40 Using the adjusting screw to put tension on the valve.

(Courtesy Honeywell)

The other hand, it is difficult to remove them without dismantling a considerable portion of the piping (unless extra fittings such as unions are used).

Flanged-end valves are used where heavy viscous media are to be controlled or where high-pressure steam service is the rule. The differ­ent types of flanged ends available for use are shown in Figure 9-45. Although flanged ends make a stronger, tighter, and more leakproof connection, their initial cost and the cost of installation is higher. This higher cost can be traced to a number of factors. For example, more metal is required in their manufacture. Moreover, flanged ends must be carefully and accurately machined before they are connected. Finally, additional parts such as gaskets, bolts, nuts, and companion flanges (to which the valve end flanges are bolted) must be provided to complete the connection.

Grooved ends are lighter in weight than flanged ends and require only an ordinary socket or speed wrench for installation or removal. The grooved end is connected to groove piping with a coupling patented by the Vitaulic Company of America.

Valves and Valve Installation

Figure 9-41 Adjusting linkage for a three-way valve. (Courtesy Honeywell)

Pipe threads in valve bodies are gauged to standard tolerances. Threaded-end valves should be installed with the proper-size wrenches. The wrench should be applied to the pipe side of the valve when installing. Doing so minimizes the possibility of distort­ing the valve body, particularly when the valve is made of a mal­leable material such as bronze. Closing the valve tightly before installation will also reduce the possibility of distortion.

Figure 9-46 illustrates the method of tightening flanged valves and fittings. Note the numbering sequence of the flange bolts in the illustration. The reason for tightening down bolts diametri­cally opposite one another is to create a gradual and uniform tightness. This results in uniform stress across the entire cross­section of the flange, which eliminates the possibility of a leaky gasket.

Valve Installing Pointers

Unless valves are installed properly, they will not operate efficiently and can cause problems in the system. There are certain precau­tions you should take when installing valves that will improve their

Q445A-F

LINKAGE KEY FITS IN

CRANKARM MOTOR SHAFT

Valves and Valve Installation

Figure 9-42 Honeywell model Q455 valve linkage connecting a motor to a water or steam valve. (Courtesy Honeywell)

Performance and minimize the possibilities of a malfunction. These precautions may be summarized as follows:

1. Always clean out a valve before installation because dirt, metal chips, and other foreign matter can foul it. This can be done by flushing the valve with water or blowing it out with compressed air.

2. Clean the piping before installing the valve. If you cannot flush or blow out the foreign matter, the ends of the pipes should be swabbed with a damp cloth.

3. Only apply paint, grease, or joint sealing compound to the pipe threads (that is, the male threads). Never apply these substances to the valve body threads because you run the risk of their getting into the valve itself and interfering with its operation.

Valves and Valve Installation

Valves and Valve Installation

Valve it is used with. (Courtesy Honeywell)

4. Install valves in a location that can be reached conveniently (see Figure 9-47). If the valve is placed so that it is awkward to reach, it sometimes may not be closed tightly enough. This can eventually cause leaks to develop in the valve.

5. When necessary, support the piping so that additional strain is not placed on the valve. Small or medium-size valves can be supported with hangers placed on either side. Large valves should always be independently suspended.

Valves and Valve Installation

Figure 9-44 Amount of tension put on the valve stem at the ends of the valve stroke is indicated by the washer inside the strain release

Mechanism. (Courtesy Honeywell)

6. Sufficient clearance is particularly important when rising stem valves are used. Failure to ensure proper clearance before installing the valve may cause damage to the disc sealing surface.

Soldering, Brazing, and Welding Valves to Pipes

The joining of valves to pipes by soldering, brazing, or welding offers certain advantages over threaded and flanged joints in reduced maintenance and repairs. Furthermore, joints of this type enable you to use lighter pipe and require fewer flanges and gas­kets. The major disadvantage is that an experienced and skilled worker is required to do the job. This can result in higher labor costs.

Fusion welding is the most commonly used method of welding a valve to a pipe. Essentially, it consists of fusing the metal of the valve and pipe connection by applying heat at a temperature above the melting point of the metal. The following two types of welds can be made: (i) a butt weld, and (2) a socket weld.

P

S

Valves and Valve Installation

LARGE MALE AND FEMALE

 

Valves and Valve Installation

SMALL MALE AND FEMALE

 

Valves and Valve Installation

RAISED FACE

 

Valves and Valve Installation

PLAIN FACE

 

LARGE TONGUE AND GROOVE

подпись: 
large tongue and groove
P SI

RING JOINT

подпись: ring jointSMALL TONGUE AND GROOVE

Figure 9-45 Various types of flanged ends used on valves.

(Courtesy Wm. Powell Co.)

Both soldering and silver brazing are procedures used to join two metals, but they differ from fusion welding in that temperatures below the melting point of the metal are used. Either a suitable sol­dering flux or a silver brazing alloy is heated to a temperature at which it will flow into the joint formed by the valve connection and pipe end. Silver brazing is replacing soldering in many applications because it is quicker and results in a stronger joint.

A more detailed description of the procedures used in soldering, brazing, and welding pipe connections is given in Chapter 8 (Pipes, Pipe Fittings, and Piping Details)’. These procedures are summarized in the following sections.

Valves and Valve Installation

Valves and Valve Installation

Figure 9-47 Install valves in a convenient, easily reached location.

Valves and Valve InstallationSoldering or Silver-Brazing Procedure

The basic procedure for soldering or silver-brazing pipe or tubing to valves is as follows:

1. Cut the tube or pipe end square, and make sure the diameter is not undersize or out of round.

2. Remove all burrs with a metal file.

3. Clean the pipe or tubing end (at least to the depth of the socket) and the inside of the valve socket with steel wool and a cloth to wipe away the residue.

4. Clean all surfaces with a suitable solvent and wipe dry.

5. Apply solder flux or silver-brazing flux to the inside of the valve socket and the outside of the pipe or tubing.

6. Insert the pipe or tubing into the valve socket until it seats against the shoulder within the socket.

7. Turn the valve and the pipe or tubing once or twice to evenly distribute the flux.

8. Make certain the valve is in open position before applying heat. A nonmetallic disc should be removed before the heat is applied. After removing the disc, the valve bonnet or bonnet

Ring should be replaced hand-tight to prevent distortion to the threaded sections when heating the valve.

9. Make certain the valve and pipe or tubing are properly sup­ported during the soldering or silver-brazing process. Any strain on the joint while cooling will weaken it.

10. Apply flame evenly around piping or tubing adjacent to valve ends until solder or brazing alloy suitable for the service flows upon contact.

11. Soldering: Apply solder to the joint between the pipe or tub­ing and the end of the valve socket. Apply the flame toward the bottom of the valve socket until all the solder is absorbed. Control the direction of the flame away from the valve body to avoid excessive heating, which causes distortion and improper functioning of the valve.

12. Silver brazing: Apply brazing alloy to the joint between the pipe or tubing and the end of the valve socket. Wave the flame over the valve hexes to draw the metal alloy into the socket, leaving a solid fillet of brazing alloy at the joint. Control the direction of the flame away from the valve body to avoid excessive heating, which causes distortion and improper func­tioning of the valve.

13. Remove all excess and loose matter from the surface with a clean cloth or brush.

Butt-Welding Procedure

The procedure for making a butt weld is as follows:

1. Machine the pipe ends for the butt-welding joint.

2. Clean the pipe ends, valve joint, and the inside of the valve socket with a degreasing agent to remove oil, grease, or other foreign materials.

3. Align by means of fixtures, and tack weld in place.

4. Make certain the valve is in the open position before applying heat. The valve bonnet should be hand-tight to prevent distor­tion or damage to the threads. Nonmetallic discs should be removed before applying heat.

5. The valve and pipe should be supported during the welding process and must not be strained while cooling.

6. Preheat the welding area 400F to 500F.

7. Depending on the welding method used (gas, arc, and so on), a butt weld is normally completed in two to four passes. The first pass should have complete joint penetration and be flush with the internal bore of the pipe. Make sure the first pass is clean and free from cracks before proceeding with the second pass. The second pass should blend smoothly with the base metal and be flush with the external diameter. Avoid excessive heat because this can cause distortion and possible malfunc­tioning of the valve.

8. Use a wire brush and a clean cloth to remove discoloration.

Socket-Welding Procedure

The procedure for making a socket weld is as follows:

1. Cut the pipe end square, making sure the diameter is not undersize or out of round.

2. Remove all burrs with a metal file.

3. Clean the pipe end, valve joint, and the inside of the valve socket with a degreasing agent to remove any oil, grease, or other foreign material.

4. Insert the pipe end into the valve socket and space by backing off the pipe after it hits against the shoulder inside the spacing collar. Tack weld in place.

5. Make certain the valve is in the open position before applying heat. Valve bonnets should be hand-tight to prevent distortion or damage to the threads. Nonmetallic discs should be removed before applying heat.

6. The valve and pipe should be supported during the welding process and must not be strained while cooling.

7. Preheat the welding area 400F to 500F.

8. A socket weld can generally be completed in two to four passes, depending on the welding method used. Make sure the first pass is clean and free from cracks before proceeding with the second pass. Avoid excessive heat because it may cause distortion to the valve bonnet.

9. Use a wire brush and a clean cloth to remove discoloration.

Posted in Audel HVAC Fundamentals Volume 2 Heating System Components, Gas and Oil Burners, and Automatic Controls


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