Absolute tightness In practice absolute tightness can never be achieved, and there will always be some degree of leakage. However, something approaching zero leakage can be obtained through welding. The type of assembly shown in Figure 8.11 is difficult to disas­semble and requires the welds at the periphery of the thin plates to be broken. Shaft seals

Absolute tightness In practice absolute tightness can never be achieved, and there will always be some degree of leakage. However, something approaching zero leakage can be obtained through welding. The type of assembly shown in Figure 8.11 is difficult to disas­semble and requires the welds at the periphery of the thin plates to be broken. Shaft sealsIt is possible to achieve a virtually leak proof fan by employing a direct driven fan having a flanged end shield motor. Even if gas escapes through the seal at the shaft extension, it is still con­tained within a totally enclosed motor housing. This should be naturally cooled and there is then no shaft seal at the non drive end.

Figure 8.11 Welded flange with added plates

The bolting together of two surfaces such as flange faces, only provides a limited tightness even when the flanges have a high degree of surface finish and the bolts are “torqued-up” to a sig­nificant value.

Sealing without joints

In certain cases, it is possible to achieve a reasonable degree of gas tightness by using a knife edge plane contact as shown in Figure 8.12. This design requires that the geometry of the con­tact surfaces is very good and that the surface roughness is minimal.

подпись: figure 8.11 welded flange with added plates
the bolting together of two surfaces such as flange faces, only provides a limited tightness even when the flanges have a high degree of surface finish and the bolts are “torqued-up” to a sig-nificant value.
 sealing without joints
in certain cases, it is possible to achieve a reasonable degree of gas tightness by using a knife edge plane contact as shown in figure 8.12. this design requires that the geometry of the contact surfaces is very good and that the surface roughness is minimal.
Other methods may also be used for fans in the gas industry, see Figure 8.13, which shows a fan arranged with shaft seals and drive through a coupling.

Absolute tightness In practice absolute tightness can never be achieved, and there will always be some degree of leakage. However, something approaching zero leakage can be obtained through welding. The type of assembly shown in Figure 8.11 is difficult to disas­semble and requires the welds at the periphery of the thin plates to be broken. Shaft seals

Figure 8.13 Direct driven leak proof fan for the gas industry

Shaft closing washer

«

подпись: «

N-

подпись: n-The shaft closing washer described in Section 8.3.3 as part of the spark minimising features may also be used as a simple seal. Provided it is made from a soft brass or similar, the hole can be of exactly the same diameter as the shaft. It will easily “run in” without causing any damage. Provided the ratio of criti­cal speed to running speed is high, the shaft deflection is low and the balance grade better than G 6.3 (preferably G 2.5), elongation of the hole will be minimal.

Absolute tightness In practice absolute tightness can never be achieved, and there will always be some degree of leakage. However, something approaching zero leakage can be obtained through welding. The type of assembly shown in Figure 8.11 is difficult to disas­semble and requires the welds at the periphery of the thin plates to be broken. Shaft sealsStuffing box

Figure 8.12 Knife edge plane contact

The example shown has a knife edge in contact with a plane surface. One of the two pieces should preferably be much more ductile than the other. This type of assembly should be re­stricted to parts less that about 100 mm for the maximum dimension.

подпись: figure 8.12 knife edge plane contact
the example shown has a knife edge in contact with a plane surface. one of the two pieces should preferably be much more ductile than the other. this type of assembly should be re-stricted to parts less that about 100 mm for the maximum dimension.
A box is filled with a soft packing, such as greased rope. This packing is compressed against the shaft by a gland. The gland is usually split as illustrated in Figure 8.14 and held in place by swivel bolts.

Absolute tightness In practice absolute tightness can never be achieved, and there will always be some degree of leakage. However, something approaching zero leakage can be obtained through welding. The type of assembly shown in Figure 8.11 is difficult to disas­semble and requires the welds at the periphery of the thin plates to be broken. Shaft sealsThe gland tightness is critical — too tight and heat will be gener­ated. There will also be a frictional power loss. If insufficiently

Gaskets

With a sealing gasket, a high level of gas tightness can be achieved with less than perfect surface quality even on larger areas. The gasket material must have good elasticity, plasticity

And low permeability. It must also have good resistance to the Figure 8.14 Components of split stuffing box and gland

Tightened there will be considerable leakage. Maintenance is therefore greater than for other types.

Figure 8.18 Section through a mechanical seal

Setscrews Comptesson nog Dnv« pn

подпись: 
figure 8.18 section through a mechanical seal
setscrews comptesson nog dnv« pn
Labyrinth seals

"M

подпись: "mThese are most commonly used and many variants exist. All however require a polished shaft, see Figure 8.15. The laby­rinth ring is in two parts, typically stainless steel or PTFE.

Fan inside

Annular spring

IJtr

Carbon ring in 2 or 3 parts

___ y.__

Absolute tightness In practice absolute tightness can never be achieved, and there will always be some degree of leakage. However, something approaching zero leakage can be obtained through welding. The type of assembly shown in Figure 8.11 is difficult to disas­semble and requires the welds at the periphery of the thin plates to be broken. Shaft seals

Force through the shaft packing to a seal ring. All the parts de­scribed above rotate with the shaft. The gland insert is fixed to the gland which is stationary, and hence rubbing takes place between this insert and the seal ring. By varying the number of gaskets between the gland and the box, the best setting for gas tightness and wear can be decided.

 

Posted in Fans Ventilation A Practical Guide


Добавить комментарий

Ваш e-mail не будет опубликован. Обязательные поля помечены *