GB2086480A - A rotary positive-displacement pump - Google Patents

Abstract

In a pump having a pressure-loaded cheek plate 14 abutting the pumping means e.g. externally-meshing gears or rotor with sliding vanes, extrusion of a seal 16 in a pressure-loading chamber 15 is prevented by an adjoining sheet of substantially stretch-resistant material such as aluminium, a fabric, or a plastics material. <IMAGE>

Description

SPECIFICATION A pressure loaded pump This invention relates to a pressure loaded pump.

Pressure loaded pumps are well known. The pressure loading is achieved by admitting fluid to a chamber and this chamber has to be sealed in order to avoid loss of fluid and therefore loss of pressure.

The known seals have not always been satisfactory.

Thus, for example, in a known construction, an O-ring seal contained in a groove in one or both of a pair of generally plain and parallel surfaces has been satisfactory at low pressures but, at higher pressures, the O-ring seal has been found to become extruded into a gap between the two surfaces. Such extrusion leads to failure of the seal. The known extrusion of the O-ring seals led to the formation of so called anti-extrusion rings having a metal collar bonded to the circumference of the O-ring. These anti-extrusion rings are also not entirely satisfactory for the sealing of pressure loaded chambers in pressure loaded pumps because of relative movement of pump parts sandwiching the seal and because of the often non-circular sometimes re-entrant shape of the chamber to be sealed.

It is an aim of the present invention to provide a pressure loaded pump having a sealing unit which is more effective than the known O-ring seals and anti-extrusion ring seals.

Accordingly, this invention provides a pressure loaded pump comprising a housing, rotary positive displacement pump means positioned in the housing, a side sealing element for engaging a side face of the pump means, a chamber in the pump which requires to be sealed to effect the pressure loading in the pump, and a sealing unit which is positioned in the chamber and which is for effecting a seal in the chamber in order to allow the pressure loading, the sealing unit comprising a sealing ring and a restrainer sheet, the restrainer sheet being made of a substantially stretch-resistant material, the restrainer sheet being of substantially the same shape as the periphery of the chamber, and the sealing ring being upstanding from the periphery of the restrainer sheet and being restrained by the restrainer sheet in substantially the same shape as the periphery of the chamber whereby the sealing ring is always positioned in a sealing shape in the chamber and is prevented by the restrainer sheet from extrusion leading to pressure leakage from the chamber.

Advantageously, the pressure loaded pump is employed for pumping fuel. The pressure loaded pump can however be employed for pumping various fluids, for example hydraulic liquids.

The sealing unit may be a one part moulded sealing unit with the sealing ring and the restrainer sheet integrally formed with each other. Alternatively, the sealing unit may be composed of a separately formed sealing ring and a separately formed restrainer sheet, the sealing ring and the restrainer sheet being subsequently bonded together.

The restrainer sheet may be made from various materials. It is presently preferred that the restrainer sheet be made from a plastics material or a metal.

The sealing ring may be made from materials presently employed for known sealing rings, including plastics materials. Generally, the sealing ring will be flexible. Preferably, the restrainer sheet extends around at least a part of the circumference of the sealing ring.

Usually, the pump means will be gear pump means or vane pump means.

Preferably, the chamber is formed in the side sealing element. The pressure loaded pump may be one in which there are a pair of movable side sealing elements. The movable side sealing elements may be axially movable side plates.

Usually, the chamber of the pump will be of a non-circular peripheral shape.

Embodiments of the invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure lisa cross section of a sealed chamber showing one form of sealing unit; Figure 2 is a cross section of a sealed chamber showing an alternative form of sealing unit; Figure 3 is a sectional side elevation of a pressure loaded gear pump having sealed pressure loading chambers; Figure 4 is a cross section on the line 4-4 of Figure 3; and Figure 5 is a cross section on the line 5-5 of Figure 3.

Referring to Figure 1, a chamber 1 is formed between the opposed generally plane surfaces of two members 2, 3. The members 2,3 have a gap 4 therebetween. A seal is provided for the chamber 1, the seal comprising a metal restrainer sheet 5 shaped according to the periphery of the chamber 1, and a flexible and compressible sealing ring 6 which is upstanding from the sheet 5. The sheet 5 is preferably made of a ductile metal such as aluminium and the ring 6 is preferably made of an elastomeric material. The sheet 5 has a flexible lip 7 formed on its outer edge, the lip 7 extending over the gap 4 between the opposed members 2, 3. Under the action of fluid pressure in the chamber 1, the sealing ring 6 will be urged against the sheet 5 and against the side wall 9 of the chamber 1.Extrusion of the sealing ring 6 through the gap 4 will be prevented by the sheet 5 and especially its lip 7.

Referring now to Figure 2, the sealing unit comprises an integrally moulded seal 8. The seal 8 is moulded to the peripheral shape of the chamber 1 to ensure that it lies against the side wall 9 of the chamber 1 and thereby seal the gap 4. The seal 8 will not extrude through the gap 4 under the action of pressure in the chamber 1. The seal 8 is of a two part construction having a restrainer sheet 10 predominantly constituted of a stretch-resistant fabric material and an inner sealing part 11 of an elastomeric material. An edge portion 20 of the part 11 forms an upstanding compressible sealing ring 20.The seal ing ring 20 is held in shape by a wrapped-arnund edge portion 21 of the restrainer sheet 10. During the moulding operation, the elastomeric material soaks into the fabric of the restrainer sheet 10 to give a satisfactory bond between the elastomeric material and the fabric material, and to make the fabric mater ial impervious to the passage of any of the fluid that may be present in the chamber 1. The stretch resistance of the fabric material for the restrainer sheet 10 will prevent extrusion ofthe elastomeric material through the gap 4 underthe action of pressure in the chamber 1.

Figures 3,4 and 5 show the application of a seal of the type shown in Figure 2 to the pressure loading area of a movable side plate in a pressure loaded hydraulic gear pump. More specifically, Figures 3,4 and 5 show two gear wheels 12 rotating in a pump housing 18 in the direction indicated by the arrow 13.

The gear wheels 12 produce a high pressure in an area to the right hand side of Figure 3 where the gear teeth 1 2a of the gear wheels 12 intersect The outlet (not shown) of the pump is connected to this high pressure area. A side plate 14 lies adjacent to the sides of the gear wheels 12 and is free to move towards and away from the sides of the teeth 12a of the gear wheels 12.

A chamber 15 is formed between the side plate 14 and a housing part 17 ofthe housing 18. This chamber 15 is of a re-entrant circumferential shape and it contains a sealing unit 16. The fluid from the high pressure side ofthe pump is admitted to the chamber 15 by a passageway which is not shown but which may for example extend through the side plate 14. This pressure will act on the side plate 14to hold it in sealing contact with the sides ofthe gear wheels 12. The sealing unit 16 effectively prevents leakage from the chamber 15.

In order to allow the desired sliding movement of the side plate 14, a clearance 19, of, for example, 0.005 inches is normally provided between the side plate 14 and the housing part 17.

It has been found that with pressure loaded hydraulic gear pumps of the above described type that are required to operate over a very wide temperature range, the known available seals tend to extrude through the clearance 19 due to the high pressures in the chamber 15, accompanied by the slight movement that takes place between the side plate 14 and the housing 18. With a sealing unit ofthe present invention, for example as shown in Figure 1 or as shown in Figure 2, the required sealing ofthe chamber 15 can be effected for a longer period of time since the sealing unit ofthe present invention will be such that the restrainer sheet will prevent extrusion of the sealing ring and thus the sealing unit will last longer. The sealing unit may be a one part moulded seal or a two part seal comprising a metal or a plastics restrainer sheet having a separate sealing ring.

If a metal our a plastics restrainersheetis employed, it is preferable that, as in the embodiment of Figure 1,the lip 7 is flexible so that underthe action of pressure in the chamber 15, the lip 7 will be forced into intimate contact with the circumferential side wall surfaces of the chambers 1, 15 to allow for slight variations in construction.

It is to be appreciated that the embodiments of the invention described above have been given by way of example only and that modifications may be effected.

Claims (11)

1. A pressure loaded pump comprising a hous ing, rotary positive displacement pump means positioned in the housing, a side sealing element for engaging a side face of the pump means, a chamber in the pump which requires to be sealed to effect pressure loading in the pump, and a sealing unit which is positioned in the chamber and which is for effecting a seal in the chamber in orderto allow the pressure loading, the sealing unit comprising a sealing ring and a restrainer sheet, the restrainer sheet made of a substantially stretch-resistant material, the restrainer sheet being of substantially the same shape as the periphery of the chamber, and the sealing ring being upstanding from the periphery of the restrainer sheet and being restrained by the restrainer sheet in substantially the same shape as the periphery of the chamber whereby the sealing ring is always positioned in a sealing shape in the chamber and is prevented by the restrainer sheet from extrusion leading to pressure leakage from the chamber.

2. A pressure loaded pump according to claim 1 in which the sealing unit is a one part moulded sealing unit with the sealing ring and the restrainer sheet being integrally formed with each other.

3. A pressure loaded pump according to claim 1 in which the sealing unit is composed of a separately formed sealing ring and a separately formed restrainer sheet, the sealing ring and the restrainer sheet being subsequently bonded together.

4. A pressure loaded pump according to any one of the preceding claims in which the restrainer sheet is made of a plastics material our a metal.

5. A pressure loaded pump according to any one of the preceding claims in which the restrainer sheet extends around at least a part of the circumference ofthe sealing ring.

6. A pressure loaded pump according to any one ofthe preceding claims in which the pump means is a gear pump means or a vane pump means.

7. A pressure loaded pump according to any one of the preceding claims in which the chamber is formed in the side sealing element.

8. A pressure loaded pump according to any one of the preceding claims in which the side sealing elements are movable side sealing elements.

9. A pressure loaded pump according to claim 8 in which the movable side sealing elements are axially movable side plates.

10. A pressure loaded pump according to any one of the preceding claims in which the chamber of the pump is of a non-circular peripheral shape.

11. Apressure loaded pump substantially as herein described with reference to the accompanying drawings.