GB2065773A - Rotary Pumps - Google Patents

Abstract

A rotary pump capable of operation at speeds in excess of 5,000 rpm without cavitation comprises a stationary body 14 defining a compartment 64 in which a quantity of a rigid porous material is mounted for rotation on a shaft 16. Liquid such as oil is fed via an inlet 42 into a channel 70 in the material and is urged by centrifugal force radially outwardly through the material to a diffuser 72, 73 in the body. The material enhances the transfer of rotary motion to the liquid. In an alternative embodiment the compartment is defined within a rotating housing 12 and the high pressure, high velocity liquid is collected in a diffuser 78 in the static body 14. A high pressure seal 82 is provided between the static body and the rotating housing. <IMAGE>

Description

SPECIFICATION Rotary Pump The present invention relates to rotary pumps.

Apart from high pressure rotary piston pumps, rotary pumps fall into two main categories, centrifugal pumps and gear pumps. In both cases the rotating parts have to run with very small clearances, and with gear pumps in particular, this requires precision machining during their manufacture which makes them expensive. They also need to be supported accurately on bearings which add to the cost, and in general, the complete unit in either case is relatively heavy and both are subject to failure from small engine debris.

A further disadvantage of centrifugal vane pumps is that the higher the speed at which they run, the more prone they become to mechanical damage due to cavitation in the liquid being pumped.

Gear pumps, although they are widely used in gas turbine engine applications, can also suffer from cavitation damage but in addition have the disadvantage that unless the liquid entering the pump is pre-pressurised they do not work very efficiently at speeds above about 3,000 rpm.

Hence, in a gas turbine engine application, where the only available power shafts are accessory drives, which for other reasons normally run at very much higher speeds, eg in excess of 20,000 rpm, a significant step-down gear train is required to drive the gear pumps, and this adds weight, cost and complexity to the engine.

An object of the present invention is to provide a rotary pump which is capable of operation at speeds in excess of 5,000 rpm but, which does not suffer from the mechanical damage experienced by conventional centrifugal vane pumps and gear pumps.

Another object of the present invention is the provision of a rotary pump for a gas turbine engine oil system which works efficiently at a relatively high speed, and which can be driven from a convenient shaft within the engine without the need for an intervening step-down gear.

According to the present invention, a rotary pump comprises a cylindrical housing having a compartment containing a rigid porous material therein, said material defining a multiplicity of flow passages therethrough, means for rotating the material about the longitudinal axis of the housing, an inlet to the compartment through which the fluid is supplied at a first pressure to a radially inner portion of the porous material and a diffusing outlet passage communicating with a radially outer part of the compartment for collecting the fluid at a second pressure, higher than the first pressure, after passage through the porous material.

The porous material preferably has an open cell or reticulated structure which allows relatively free passage of liquid therethrough but also provides a large surface area which contacts the liquid to drive the liquid.

Since there is also communication transversely of liquid pressure through the interstices of the material structure, this form of pump is pressure balanced and there are no side loads on the supporting bearings.

The porous material may be connected for the rotation to a shaft within a static part of the housing, or alternatively, the housing itself may be rotatable, and the porous material may be connected for rotation with the housing.

In such a pump the passages or interstices, within the porous material run full of the liquid.

Since they are very much smaller than those in a vane pump, and since they encompass the liquid, there is a much more positive drive to the liquid and less slippage within the liquid, which reduces cavitation. Further, since the liquid is supplied at a radially inner part of the porous material and progresses by centrifugal action to a radially outer part, there are none of the inlet problems associated with gear pumps and the new pump is not limited in its speed of operation by such problems.

Examples of the invention will now be more particularly described with reference to the accompanying drawings in which: Figure 1 is a side elevation of a device including two alternative forms of pump of the present invention in a device forming part of a gas turbine engine oil system, and, Figure 2 is a cross-sectional view on the line A-A of Figure 1.

Referring now to the drawings, there is shown a device as described in our patent application No 7944038 entitled "Fluid Processing Devices" of the same date, reference to which is hereby incorporated into this specification. The device as illustrated herein includes two embodiments of the pump of the present invention. Only those parts of the device relevant to the present invention are shown in detail, the remainder being shown in ghost outline.

The device includes a rotatable body part 1 2 and a static body part 14. The rotatable body part is driven by a shaft 16 which in this example is an extension of the shaft of an engine gearbox 10.

One embodiment of the pump is illustrated within the static body part 14. A compartment 64 is defined between confronting surfaces of the body 14 and the gear box 10. An inlet passage 42 communicates via a drilling 62 with the compartment 64 in which a quantity of rigid porous material is supported for rotation with the shaft 1 6. The porous material may be of the type sold under the trade name of RETIMET (Registered Trade Mark) by Dunlop Limited.

The porous material is clamped between a flange 66 on a sleeve 15, which is rotatable with the shaft, and a washer 68. Alternatively, the material may be sandwiched between spokes which may be clamped at their radially inner ends for rotation with the shaft.

The drilling 62 is arranged to deliver oil from the engine oil tank via one of the passages 42 to a channel 70 in the radially inner region of the spinning porous material. Centrifugal forces on the oil then cause it to flow through the material gaining energy all the time until it is delivered at a much higher pressure and with high tangential velocity to an outlet passage 72 in a static ring 73 at the radially outer periphery of the compartment. The passage 72, which is preferably angled to minimise entry pressure losses as the oil passes into it, extends circumferentially and is shaped as a diffuser to regain pressure from the high tangential velocity of the oil. The passage 72 communicates with a tapered passage 74 in the body 14 from which an external pipe (not shown) removes the oil to a location of use.

Because the passages in the porous material are very small the side walls of the passages, are very close together. There is thus no room for the oil to circulate within the passages and the tendency of the pump to cavitate is much reduced.

Since there are no entry problems as the oil enters the compartment the pump can be run at a higher speed than a conventional pump to give the required flow at the required pressure. This enables it to be driven by the same relatively high speed shaft as the other components of the device 11. Hence the step-down gearing required for the current gear pump in a gas turbine engine oil system can be eliminated.

The rotating material runs with the smallest possible clearance from the side walls of the gear box 10 and the body 14 to minimise leakage.

However, the rotation of the material will tend to drive any liquid in the clearance outwardly so that leakage is virtually eliminated.

Because of the communication of pressure transversely through the material via the interstices in it there is no side load on the material to effect the bearing 18.

The applications of this new pump are not limited to the gas turbine engine field. It can clearly be used to replace any gear pump or centrifugal vane pump.

Variations on the design of pump described above are possible foe example, the housing may be rotatable, the porous material being connected to rotate with it. Such an embodiment can be seen in Figure 2 where compartment 34 of the rotatable body part 12 of the device can be seen to extend radially outwardly of compartment 36.

Process liquid, in this case oil from compartment 36 is passed into compartment 34 at the radially innermost region thereof. The compartment 34 is filled with the porous material and the liquid passes through the porous material, gaining pressure and velocity, and leaves the material at the radially outermost region of the compartment.

From the compartment the liquid passes via one or more apertures 76 into a diffusing passage 78 in the static part 14 of the device. The diffusing passage-may be made in a separate ring 80 for ease of manufacture which then communicates in turn with a tapered driling (not shown) in the static part 14, but which is as described with reference to the passages 72, 74 above..

In this embodiment a high pressure seal 82 is provided which prevents escape of the high pressure oil from between the rotating and static parts of the pump.

Although, throughout this specification RETIMET has been referred to as an appropriate material for the compartments other materials may be used. The requirements of the material are that it should be rigid enough to withstand the rotation, it should have interconnected cells or passages so that it is porous to the liquid and provides an acceptably low loss of fluid pressure due to friction.

Claims (5)

Claims

1. A rotary pump comprising a cylindrical housing having a compartment containing a rigid porous material therein, said material defining a multiplicity of flow passages therethrough, means for rotating the material about the longitudinal axis of the housing, an inlet to the compartment through which the fluid is supplied at a first pressure to a radially inner portion of the porous material and a diffusing outlet passage communicating with a radially outer part of the compartment for collecting the fluid at a second pressure, higher than the first pressure, after passage through the porous material.

2. A rotary pump as claimed in claim 1 and in which the housing is static and the porous material is rotatable within the housing.

3. A rotary pump as claimed in claim 1 and in which the housing is rotatable and the porous material rotates with the housing.

4. A rotary pump as claimed in any preceding claim and in which the rigid porous material has an open cell or reticulated structure.

5. A rotary pump subatantially as hereinbefore described with reference to the accompanying drawings.