GB2054067A

GB2054067A - Seals

Info

Publication number: GB2054067A
Application number: GB8022214A
Authority: GB
Original assignee: Crane Packing Ltd
Current assignee: Crane Packing Ltd
Priority date: 1979-07-06
Filing date: 1980-07-07
Publication date: 1981-02-11

Abstract

A seal for use in association with a clearance seal, on rotating equipment having a pair of relatively rotatable components 1, 2 to provide a fluid-tight seal, when the components are stationary; comprising a pair of seal face members 3, 7, each seal face member being associated in fluid-tight manner with a different one of the relatively rotatable components, all being arranged such that they are urged into sealing contact with one another by springs 10 when the rotatable components are stationary, and are urged apart by fluid pressure acting in a chamber when there is relative movement between the components. <IMAGE>

Description

SPECIFICATION Seals This invention relates to improvements in seals for use in conjunction with clearance seals.

On rotating equipment, in particular pumps, clearance seals such as bushes, labyrinths, wind back seals and centrifugal seals are often used.

These seals generally function by creating a back pressure upon rotation, this back pressure opposing the fluid pressure in the equipment. The major disadvantage of such seals is that when the equipment is stationary, the liquid within the equipment can leak out freely, whether it is pressurised or not. In order to overcome this problem a secondary, stand still seal, must be included which operates when the equipment is in the static condition. In order to minimise wear on the stand still seal it is desirable that it should be operative only when the equipment is in the static condition.

According to one aspect of the present invention, a seal for use in association with a clearance seal on rotating equipment having a pair of relatively rotatable components, comprises a pair of seal face members, one seal face member being associated, in fluid-tight manner, with one of the components and the other seal face member associated in fluid-tight manner, with the other component; spring means adapted to urge the seal face members into sealing engagement with one another and means adapted to force the seal face members apart in response to an increase in pressure developed upon rotation of one component with respect to the other.

Preferably the means to force the seal face members apart is in the form of a concentric bellows arrangement or may be provided by an inflatable unit. This means may be actuated in response to an increase in fluid pressure developed across the equipment, or in the back pressure developed by the clearance seal, upon rotation of one component with respect to the other.

Two embodiments of the present invention are now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 illustrates a stand still seal suitable for use in conjunction with a clearance seal in a pump housing; and Figure 2 illustrates an alternative form of stand still seal, in accordance with the present invention.

The stand still seal illustrated in Figure 1 is intended for use in a pump, in association with a clearance seal (not shown). The stand still seal comprises a seat or first seal face member 3 secured to the pump shaft 1 by locking sleeves 5 and 6 and sealed thereto by means of an O-ring 4.

The second seal face member 7 is mounted in a carrier ring 8 by means of a rubber cup or gasket 9. The carrier 8 and thus the seal face member 7 is located in a housing 14 associated with the pump housing 2, so that it may move axially with respect to the shaft 1. A plurality of radially spaced springs 10 act between the carrier 8 and a plate 11 to urge the seal face member 7 into contact with seat 3. The plate 11 is secured to the seal housing 14 or pump housing 2 and is adjustable axially so that the load applied by the springs 10 may be adjusted as required.

A pair of concentric metal bellows 12, 13 are secured between the housing 14 and the carrier 8 in order to provide a pressure chamber 1 9. The pressure chamber 1 9 is connected via tube 1 8 to the discharge side of the pump or to a region of the clearance seal which is at high pressure only when the pump is in operation.

A pair ofcdirt excluders, in the form of lip seals 15, 16, are positioned between the housing 14 and shaft 2 and are retained in position by a circlip 1 7. The housing 14 of the stand still seal is bolted or secured by some other clamping means (not shown) to the pump housing 2.

In operation, when the pump is stationary the pressure inside the chamber 1 9 is low and the springs 10 force the seal face member 7 into sealing engagement with the seat 3. When the pump is started and the clearance seal begins to function, the pressure in the chamber 1 9 increases with the increasing pressure on the discharge side of the pump or in the high pressure region of the clearance seal, to oppose the load applied by the springs 10 and push the carrier 8 axially thus moving the seal face member 7 clear of the seat 3.

Again when the pump is stopped and the clearance seal ceases to function, the pressure in the chamber 1 9 decreases and the springs 10 force the seal face member 7 back into contact with the seat 3.

By means of the adjustable plate 1 ,the load applied by the springs 10 may be adjusted to suit the difference in pressure experienced in the chamber 1 9 when the pump is in operation and when it is stationary. In this manner the stand still seal can be arranged to operate at the appropriate time.

While in the embodiment described above metal bellows 12, 13 are used these may be equally well be made of other materials, for example PTFE or rubber.

In the alternative embodiment illustrated in Figure 2 the concentric bellows arrangement is replaced by an inflatable unit 21 which is positioned between the carrier 8 and the housing 14. Also in this embodiment the radially spaced springs 10 are replaced by an annuiar spring element 22. Otherwise the construction of the seal is the same as that illustrated in Figure 1 and they function in the same manner.

Various modifications may be made without departing from the invention. For example while in the above embodiments, the means adapted to force the seal face members apart, is connected directly with a region of the pump or the clearance seal which is at high pressure only when the pump is in operation, it may be connected to a secondary source of pressurised fluid which is actuated by movement of one component of the pump with respect to the other.

Claims

1. A seal for use in association with a clearance seal, on rotating equipment having a pair of relative rotatable components, comprising a pair of seal face members, one seal face member being associated, in fluid-tight manner, with one of the components and the other seal face member associated, in fluid-tight manner, with the other component; spring means adapted to urge the seal face members into sealing engagement with one another and means adapted to force the seal face members apart in response to an increase in fluid pressure developed upon rotation of one component with respect to the other.

2. A seal according to Claim 1 in which the means adapted to force the seal face members apart is in the form of a concentric bellows arrangement.

3. A seal according to Claim 1 in which the means adapted to force the seal face members apart is in the form of an inflatable unit.

4. A seal according to any one of the preceding Claims in which the means adapted to force the seal face members apart acts in response to an increase in fluid pressure developed across the equipment, when one component rotates relative to the other.

5. A seal according to any one of Claims 1 to 3 in which the means adapted to force the seal face members apart acts in response to an increase in the back pressure developed by a clearance seal, upon rotation of one component with respect to the other.

6. A seal according to any one of the preceding Claims in which the means adapted to force the seal face members apart is connected directly with a region of the equipment or associated clearance seal which is at relatively high pressure when one component rotates relatively to the other and relatively low pressure when there is no relative movement between the components.

7. A seal according to any one of Claims 1 to 6 in which the means adapted to force the seal face members apart is actuated by pressurised fluid from a secondary source.

8. A seal according to any one of the preceding Claims in which the spring means comprises a plurality of radially spaced compression springs acting upon one of the seal face members.

9. A seal according to any one of Claims 1 to 7 in which the spring means comprises an annular spring element which acts upon one of the seal face members.

10. A seal face member according to any one of the preceding Claims in which means is provided for adjusting the load applied by the spring means, whereby the difference in pressure required to engage or disengage the seal face members, may be adjusted.

11. A seal for use in association with a clearance seal, on rotating equipment having a pair of relatively rotatable components, substantially as described herein with reference to, and as shown in, Figure 1 of the accompanying drawings.

12. A seal for use in association with a clearance seal on rotating equipment having a pair of relatively rotatable components, substantially as described herein with reference to, and as shown in, Figure 2 of the accompanying drawings.