GB2118641A - Seal assembly - Google Patents

Abstract

A seal assembly for providing a seal between a housing 11 which defines a fluid chamber 28 and a rotatable shaft 9 comprises; primary 16, 25 and secondary 27, 30 sealing means defining a seal chamber therebetween, into which a sealing fluid may be introduced; the secondary sealing means 27, 30 permitting leakage of the sealing fluid from the seal chamber to the fluid chamber 28, when the pressure of the sealing fluid is in excess of the pressure in the fluid chamber and providing a fluid tight seal between the seal chamber and fluid chamber, when the pressure in the fluid chamber is in excess of the pressure of the sealing fluid. In a second embodiment the secondary sealing means comprises a flexible annular diaphragm fixed to the housing and a collar rotatable with the shaft. <IMAGE>

Description

SPECIFICATION Seal assembly This invention relates to a seal assembly for providing a seal between a housing which defines a fluid chamber and a rotatable shaft which passes through the housing into the chamber.

When rotary mechanical face seals are used in pumps and the like, to provide a seal between the pump housing and the shaft, it is necessary to provide liquid about the face seal, in order to lubricate and cool the sealing faces. It is convenient to use the liquid passing through the pump for this purpose. However, if the liquid is dirty, then this may lead to excessive wear and clogging problems. These problems may be overcome by introducing clean liquid into the area surrounding the face seal. If this clean liquid is introduced at a pressure in excess of the operating pressure of the pump, it will keep the dirty liquid away from the face seal.

The present invention provides a secondary sealing device, which prevents the dirty liquid from reaching the face seal, if the supply of clean liquid should fail.

According to one aspect of the present invention, a seal assembly for providing a seal between a housing which defines a fluid chamber and a rotatable shaft which passes through the housing into the chamber, comprises: a primary sealing device arranged to provide a permanent seal between the shaft and housing, a secondary sealing device positioned between the shaft and the housing on the fluid chamber side of the primary sealing device to define a seal chamber therebetween and an inlet opening into said seal chamber, said inlet being adapted for connection to means for providing a supply of sealing fluid at a pressure in excess of the operating pressure in the fluid chamber and said secondary sealing device being arranged to provide; a sole outlet for sealing fluid from the seal chamber, when the pressure of sealing fluid in the seal chamber is in excess of the operating pressure in the fluid chamber and; a fluid tight seal between the seal chamber and fluid chamber, when the operating pressure in the fluid chamber exceeds the pressure of sealing fluid in the seal chamber.

Various embodiments of the invention are now described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a sectional elevation of a seal assembly formed in accordance with the present invention; and Figure 2 is a sectional elevation of an alternative form of seal assembly formed in accordance with the present invention.

The seal assembly illustrated in Figure 1 is adapted to fit in the stuffing box 10, between a pump housing 11 and shaft 9. The seal assembly is of cartridge construction in order to facilitate fitting and replacement.

The seal assembly comprises an adapter ring 12, which locates about the cylindrical outer end wall of the stuffing box 10 and is sealed thereto by means of elastomeric O-ring 1 3. The adapter ring 1 2 is located in position by means of a locking plate 14 which is bolted to the end of the stuffing box 10, with a gasket 1 5 interposed therebetween. An annular seat 1 6 is provided on the internal diameter of the clamping plate 14 and is located and sealed with respect thereto by means of a gasket 1 7. The clamping plate 14 is also provided with an inlet 1 8 which opens into the stuffing box 10.

A sleeve 20 which is co-axial with, but spaced radially from, the adapter ring 12, is mounted upon the shaft 11 and is secured thereto by locking ring 21, circumferentially spaced grub screws 22 engaging the shaft 11 and sleeve 20.

The sleeve 20 is sealed to the shaft 11 by means of elastomeric O-ring 23.

An annular seal face member 25 is mounted about the sleeve 20. This seal face member 25 is sealed to the sleeve 20 and urged into sealing contact with the seat 16, by means 26 which acts against a flange 27 on the sleeve 20. The means 26 may be any of the conventional arrangements for providing both sealing and axial loading of the seal face member 25; for example, a resilient bush, resilient bellows unit, a flexible bellows unit or diaphragm with auxiliary spring means, or spring means with auxiliary sealing means between the seal face member 25 and sleeve 20.

The side of the flange 27 facing the chamber 28 defined by the pump housing 11 is provided with an annular projection 29. An annular sealing element 30 is provided in the space 31 between the flange 27 and the end of the adapter ring 12, and is free to move axially therein. The sealing element 30 has a radially outwardly directed lip 32 which engages the cylindrical surface of the adapter ring 12; to provide a seal therebetween.

The sealing element 30 is also provided with an inwardly directed flange 33, but this is spaced from the surface of the sleeve 20.

The locking collar 21 abuts against a setting plate 35 mounted upon the clamping plate 14, in order to provide axial location of the shaft 9.

In operation, the seat 16 and seal face member 25 will provide a permanent seal between the pump housing 11 and shaft 9. Under normal operating conditions clean water is introduced into the seal chamber defined between the face seal 1 6, 25 and the seal 30 through the inlet 18, from a suitable source (not shown), at a pressure in excess of the operating pressure in the pump chamber 28. This clean water, which is introduced in the vicinity of.the sealing faces of the seat 1 6 and seal face member 25, will act as a lubricant and cool the sealing faces, and also being at a higher pressure that the liquid in the pump chamber 28, will keep that liquid which may be dirty, away from the sealing faces. The clean water will leak past the sealing element 30 into the pump chamber 28.

If the supply of clean water should fail for some reason the excess pressure of liquid in the pump chamber 28 will act against the flange 33 of the sealing element 30 and force it into sealing engagement with the projections 29, thereby preventing the dirty liquid from the pump chamber 28, from reaching the sealing faces of the seal face member 25 and seat 16. A non-return valve may be provided in the clean water supply line, so that if the supply fails, clean water will remain in the stuffing box to cool and lubricate the sealing faces, so that the pump may be used while the flow of clean water is reinstated.

In the embodiment iliustrated in Figure 2, the seal face member 40 is mounted on and sealed with respect to the shaft 9, externally of the housing 11, by means of a resilient bellows unit 41 which is clamped to the shaft 9, by means of a ring 42 secured by a tangential bolt 43. As with the embodiment described with reference to Figure 1 the bellows unit 41 may be replaced by other equivalent means conventionally used in mechanical face seais.

The seal face member 40 is urged by the bellows unit 41 into sealing engagement with a seat 44, formed on the outer surface of a plate 45, this plate 45 being bolted to the housing 11, an inlet is also provided through the plate 45 into the seal chamber 47.

A perforated annular metal plate 50 and annular diaphragm 51 are clamped together at their outer peripheries, between the plate 45 and the housing 11, so that they extend radially towards the shaft 9, but their inner peripheries are spaced from the shaft 9.

An annular collar 53, which extends radially beyond the inner periphery of the diaphragm 51, and which has a small axial clearance therefrom on the side nearest the face seal 40, 44, is mounted for rotation on the shaft 9.

As with the first embodiment, the seal face member 40 and seat 44 will provide a permanent seal between the shaft 9 and housing 11. Under normal operating conditions clean water is introduced into the seal chamber 47, to lubricate and cool the sealing faces of the seal face member 40 and seat 44, and also to prevent liquid from the pump chamber reaching these faces. The clean water will again leak past the diaphragm 51 into the pump chamber 28. If the supply of clean water should fail, then the pressure of liquid in the pump charnber 28, will force the diaphragm 51 into sealing engagement with the collar 53, thereby preventing the dirty water, in the pump chamber 28, from reaching the sealing faces of the seal face member 40 and seat 44.

In the embodiments described above, under normal operating conditions, the sealing element 30 or diaphragm 51 will engage only stationary surfaces and they are not brought into contact with relatively rotating surfaces unless the supply of clean sealing fluid fails. These members will not therefore be subject to wear under normal operating conditions and should consequently be in an operable condition, when required in an emergency.

Various modifications may be made without departing from the invention. For example, in the second embodiment, instead of mounting the diaphragm 51 with respect to the housing 11, it may be mounted on the collar 53 and arranged to engage an adjacent portion of the housing 11, in the event of failure of the clean sealing fluid supply.

Claims (9)

1. A seal assembly for providing a seal between a housing which defines a fluid chamber and a rotatable shaft which passes through the housing into the chamber, comprising: a primary sealing device arranged to provide a permanent seal between the shaft and housing, a secondary sealing device positioned between the shaft and the housing on the fluid chamber side of the primary sealing device to define a seal chamber therebetween and an inlet opening into said seal chamber, said inlet being adapted for connection to means for providing a supply of sealing fluid at a pressure in excess of the operating pressure in the fluid chamber and said secondary sealing device being arranged to provide; a sole outlet for sealing fluid from the seal chamber, when the pressure of sealing fluid in the seal chamber is in excess of the operating pressure in the fluid chamber and; a fluid tight seal between the seal chamber and fluid chamber, when the operating pressure in the fluid chamber exceeds the pressure of sealing fluid in the seal chamber.

2. A seal assembly according to claim 1 in which the primary sealing device is a mechanical face seal.

3. A seal assembly according to claims 1 or 2 in which the secondary sealing device comprises an annular sealing element mounted between the shaft and an opposed cylindrical surface of or associated with the housing, said sealing element being slidable axially with respect to the shaft and housing and being in fluid tight engagement with one of the opposed surfaces, an annular abutment means being provided on the other of said opposed surfaces, on the seal chamber side of the sealing element, so that an excess pressure on the fluid chamber side of the sealing element will force the sealing element into fluid tight engagement with the annular abutment.

4. A seal according to claim 3 in which the sealing element makes fluid tight sliding engagement with a cylindrical surface of or associated with the housing and an annular abutment is provided on the shaft.

5. A seal assembly according to claim 1 or 2 in which the secondary sealing device comprises a flexible annular diaphragm which is secured to either the shaft or the housing and is supported radially on the side adjacent the fluid chamber; and annular abutment rneans is provided on the other component on the seal chamber side of the diaphragm; said annular means and diaphragm overlapping radially but being spaced axially, so that when there is an excess pressure on the fluid chamber side of the diaphragm, the diaphragm will be deflected into engagement with the opposed radial surface of the annular abutment, to form a fluid tight seal between the shaft and housing.

6. A seal assembly according to claim 5 in which the flexible diaphragm is supported on the fluid chamber side, by means of a rigid perforated plate.

7. A seal assembly according to any one of claims 1 to 6 in which the primary and secondary sealing devices are preassembled in a cartridge construction.

8. A seal assembly according to any one of the preceding claims in which the means for providing sealing fluid to the seal chamber, is provided with a non-return valve.

9. A seal assembly substantially as described herein with reference to, and as shown in, Figure 1 or Figure 2.