GB2061413A

GB2061413A - A seal assembly

Info

Publication number: GB2061413A
Application number: GB8021078A
Authority: GB
Original assignee: Rockwell International Corp
Current assignee: Boeing North American Inc
Priority date: 1979-10-29
Filing date: 1980-06-27
Publication date: 1981-05-13
Also published as: FR2468804B1; CA1157062A; DE3032674A1; AU538118B2; FR2468804A1; AU5866280A; GB2061413B; JPS5666491A

Abstract

A seal assembly between relatively rotating parts has chambers 20, 22 and 24 interposed between labyrinth seals 12, 14 and 16, and a face type seal 18. Fluid leaking through the seal 12 is accumulated in the chamber 20 and is maintained at a predetermined pressure by a vent 21. Some of the fluid in the chamber 20 leaks through the seal 14 into the chamber 22. To prevent leakage of fluid beyond the chamber 22, a purge fluid is introduced through an inlet 26 into the chamber 24 and leaks through the seal 16 into the chamber 22. The pressure of the purge fluid is greater than the fluid pressure in the chamber 22, but less than the fluid pressure in the chamber 20. An outlet conduit 28 serves to drain fluid from the chamber 22. <IMAGE>

Description

SPECIFICATION A seal assembly This invention relates to seal assemblies suitable for rotating machinery, e.g., centrifugal coal slurry pumps.

Almost as long as there have been rotating pumps, the need has been recognized for seals to prevent leakage of the fluids about the drive shaft.

In coal slurry pumps where the material being pumped is gritty and abrasive, such seals have to prevent jamming and/or erosion of the components. To overcome this problem, the prior art has proposed to inject a clean purge fluid into the seal cavity under high pressure to exclude the slurry therefrom. The need for a high-pressure purge fluid greatly complicates the structure of the seal. Moreover, the purge fluid often reverses the process and leaks into the pump chamber, thereby contaminating the material being pumped. Thus, none of the prior art pumps have been entirely satisfactory.

These disadvantages of the prior art are overcome with the present invention which provides a seal assembly which can be used as a pump seal and which greatiy reduces the pressure requirements of the seal and can prevent the purge fluid from leaking into the pump chamber.

According to the present invention there is provided a seal assembly comprising a series of seal devices between two parts rotatable relative to each other, a plurality of chambers interposed between the seal devices, a first one of the chambers being disposed to receive fluid tending to leak through a first of the seal devices into the seal assembly, a second one of the chambers having an inlet for introducing a purge fluid, and a third of the chambers being interposed between the first and second chambers to receive fluid leaked from the first and second chambers.

Such a seal assembly can be operated with the pressure in the first chamber limited to a predetermined value greater than the pressure of purge fluid supplied to the second chamber, while the third chamber is maintained at a pressure lower than the pressure of the purge fluid.

The invention will be described in more detail, by way of example, with reference to the accompanying drawing which shows a vertical section through a seal mechanism embodying the present invention.

The figure shows a seal assembly 2, for a centrifugal coal slurry pump having an impeller 4 rotatable by a drive shaft 6 within the working chamber 8 of a housing 10. The seal assembly 2 comprises three labyrinth seals 12, 14 and 16, and a face-type seal 1 8. The pressure of the slurry in the working chamber 8 may be well in excess of 1000 psi (6895kPa) and will force some of the slurry through the impeller labyrinth seal 12.To accommodate this leakage, a chamber 20 is provided between the impeller labyrinth seal 12 and the primary labyrinth seal 14, and a vent 21 serves to connect the chamber 20 with a lowpressure location in the pump to limit the pressure within the chamber 20 to about 500-600 psi (3447-41 37kPa). Additional chambers 22 and 24 are located one between the primary labyrinth seal 14 and the secondary labyrinth seal 16, and the other between the secondary labyrinth seal 1 6 and the face seal 18. Some of the slurry from the chamber 20 will leak through the primary labyrinth seal 14 into the chamber 22. It has been found that the fluid pressure in the chamber 22 will be about 200 psi (1379kPa).To counteract this, purge fluid which is compatible with the slurry, such as kerosene, is supplied to the chamber 24 via an inlet conduit 26 from a suitable source (not shown), and is delivered at a pressure greater than that of the slurry in the chamber 22.

For example, the purge fluid may be supplied to the chamber 24 at a pressure of about 250 psi (1724kPa). In addition, an outlet conduit 28 serves to drain fluid from the chamber 22 to suitable point exterior to the pump In use, slurry from the working chamber 8 leaks through the impeller labyrinth seal 12 into the chamber 20 at reduced pressure and some of this slurry leaks past the primary labyrinth seal 14 into the chamber 22 where it meets the counterflow of purge fluid which has been introduced into the chamber 24 and has leaked through the secondary labyrinth seal 1 6. This arrangement prevents further outward leakage of the slurry and also prevents contamination of the slurry in the working chamber 8 by the purge fluid.

1. A seal assembly comprising a series of seal devices between two parts rotatable relative to each other, a plurality of chambers interposed between the seal devices, a first one of the chambers being disposed to receive fluid tending to leak through a first of the seal devices into the seal assembly, a second one of the chambers having an inlet for introducing a purge fluid, and a third of the chambers being interposed between the first and second chambers to receive fluid leaked from the first and second chambers.

2. A seal assembly according to claim 1, wherein the first seal device is a first labyrinth seal a second labyrinth seal is interposed between the first chamber and the third chamber; and a third labyrinth seal is interposed between the third chamber and the second chamber.

3. A seal assembly according to claim 1 or 2, having a face type seal on the side of the second chamber remote from the third chamber.

4. A seal assembly according to claim 1,2 or 3, further comprising a vent connected to the first chamber to limit the fluid pressure in the first chamber to a first predetermined pressure.

5. A seal assembly according to claim 4, comprising a source of purge fluid at a second predetermined pressure connected to the inlet to the second chamber.

6. A seal assembly according to claim 5, wherein the second predetermined pressure is less than the first predetermined pressure.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION A seal assembly This invention relates to seal assemblies suitable for rotating machinery, e.g., centrifugal coal slurry pumps. Almost as long as there have been rotating pumps, the need has been recognized for seals to prevent leakage of the fluids about the drive shaft. In coal slurry pumps where the material being pumped is gritty and abrasive, such seals have to prevent jamming and/or erosion of the components. To overcome this problem, the prior art has proposed to inject a clean purge fluid into the seal cavity under high pressure to exclude the slurry therefrom. The need for a high-pressure purge fluid greatly complicates the structure of the seal. Moreover, the purge fluid often reverses the process and leaks into the pump chamber, thereby contaminating the material being pumped. Thus, none of the prior art pumps have been entirely satisfactory. These disadvantages of the prior art are overcome with the present invention which provides a seal assembly which can be used as a pump seal and which greatiy reduces the pressure requirements of the seal and can prevent the purge fluid from leaking into the pump chamber. According to the present invention there is provided a seal assembly comprising a series of seal devices between two parts rotatable relative to each other, a plurality of chambers interposed between the seal devices, a first one of the chambers being disposed to receive fluid tending to leak through a first of the seal devices into the seal assembly, a second one of the chambers having an inlet for introducing a purge fluid, and a third of the chambers being interposed between the first and second chambers to receive fluid leaked from the first and second chambers. Such a seal assembly can be operated with the pressure in the first chamber limited to a predetermined value greater than the pressure of purge fluid supplied to the second chamber, while the third chamber is maintained at a pressure lower than the pressure of the purge fluid. The invention will be described in more detail, by way of example, with reference to the accompanying drawing which shows a vertical section through a seal mechanism embodying the present invention. The figure shows a seal assembly 2, for a centrifugal coal slurry pump having an impeller 4 rotatable by a drive shaft 6 within the working chamber 8 of a housing 10. The seal assembly 2 comprises three labyrinth seals 12, 14 and 16, and a face-type seal 1 8. The pressure of the slurry in the working chamber 8 may be well in excess of 1000 psi (6895kPa) and will force some of the slurry through the impeller labyrinth seal 12.To accommodate this leakage, a chamber 20 is provided between the impeller labyrinth seal 12 and the primary labyrinth seal 14, and a vent 21 serves to connect the chamber 20 with a lowpressure location in the pump to limit the pressure within the chamber 20 to about 500-600 psi (3447-41 37kPa). Additional chambers 22 and 24 are located one between the primary labyrinth seal 14 and the secondary labyrinth seal 16, and the other between the secondary labyrinth seal 1 6 and the face seal 18. Some of the slurry from the chamber 20 will leak through the primary labyrinth seal 14 into the chamber 22. It has been found that the fluid pressure in the chamber 22 will be about 200 psi (1379kPa).To counteract this, purge fluid which is compatible with the slurry, such as kerosene, is supplied to the chamber 24 via an inlet conduit 26 from a suitable source (not shown), and is delivered at a pressure greater than that of the slurry in the chamber 22. For example, the purge fluid may be supplied to the chamber 24 at a pressure of about 250 psi (1724kPa). In addition, an outlet conduit 28 serves to drain fluid from the chamber 22 to suitable point exterior to the pump In use, slurry from the working chamber 8 leaks through the impeller labyrinth seal 12 into the chamber 20 at reduced pressure and some of this slurry leaks past the primary labyrinth seal 14 into the chamber 22 where it meets the counterflow of purge fluid which has been introduced into the chamber 24 and has leaked through the secondary labyrinth seal 1 6. This arrangement prevents further outward leakage of the slurry and also prevents contamination of the slurry in the working chamber 8 by the purge fluid. CLAIMS

7. A seal assembly according to any preceding claims, further comprising a drain connected to the third chamber to drain off fluid from the third chamber.

8. A method of operating a seal assembly according to claim 1, wherein the pressure in the first chamber is limited to a predetermined value greater than the pressure of purge fluid supplied to the second chamber, while the third chamber is maintained at a pressure lower than the pressure of the purge fluid.

9. A seal assembly substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.