GB2167495A - Cooling a pump drive coupling - Google Patents

Abstract

A mechanical pump, e.g. a blower of the intermeshing vane type, has its drive shaft 4 terminating in a drive rotor 10 adapted to be magnetically coupled to a co-operating member (not shown) connected to a prime mover effective to produce rotation of the drive shaft, the rotor being enclosed within a non-ferromagnetic cap 11 which is sealed to the body 8 of the pump adjacent the drive shaft, fluid transfer means 18, 20 being provided to bring cooling fluid into heat exchange relationship with the rotor whereby in use to reduce its rise in temperature. A water cooled heat exchanger 22 is provided in a sump for the cooling fluid. <IMAGE>

Description

SPECIFICATION Improvements in mechanical pumps This invention relates to mechanical pumps and is directed to pumps having magnetic drive couplings. The invention is particularly, though not exclusively concerned with mechanical blowers of the type comprising intermeshing vanes rotating within a pump chamber embodied in the body of the pump.

It is now well known to employ a magnetic drive coupling between a mechanical pump and its prime mover which may be an electric motor or the like. Such couplings typically comprise an outer sleeve which generally is of permanent magnetic material of high coercivity and which is mechanically coupled for rotation to the electric motor prime mover. This outer sleeve is magnetically coupled to an inner rotor in the form of a squirrel cage which rotates substantially in synchronism with the driven outer sleeve and which comprises the drive element for the pump.

The main advantage of such magnetic couplings is that they enable the squirrel cage drive rotor to be totally and hermetically enclosed within a nonferromagnetic cap or the like which can be interposed between the squirrel cage and the outer magnetic sleeve and which can be sealed into the body of the pump. An arrangement of this type reduces the leakage of gas through the bearings and seals which are effective to support the pump drive shaft and increases the overall efficiency of the pump.

One major disadvantage of a sealing cap or the like is that it reduces the potential loss, by radiation or by convection, of heat generated in the squirrel cage during operation of the pump. The resultant rise in cage temperature produces heat transfer along the pump shaft and can induce a corresponding and unacceptable rise in temperature both within the body of the pump and in particular in any oils or other fluids used for pump lubrication.

Any excess rise in pump temperature can have a detrimental effect on pumping efficiency while an excessive rise in oil temperature can produce rapid deterioration and possibly decomposition of the oil. This further reduces both pump efficiency as well as operational life between expensive pump overhauls.

It is accordingly an object of the present invention to produce a mechanical pump construction of the type herein disclosed in which the effects of heat generated in the magnetic drive coupling is reduced.

The present invention according to its broadest aspect comprises a mechanical pump having its drive shaft terminating in a drive rotor adapted to be magnetically coupled to a co-operating member connected to a prime mover effective to produce rotation of the drive shaft, the rotor being enclosed within a non-ferromagnetic can which is sealed to the body of the pump adjacent the drive shaft, means being provided to bring cooling fluid into heat exchange relationship with the rotor whereby in use to reduce its rise in temperature.

Ideally, the cooling fluid is circulated into direct contact with one or more surfaces of the drive rotor.

In the case where the pump is a lubricated pump, the cooling fluid comprises the lubrication oil and is circulated over the drive rotor from the conventional sump generally provided at the base of the pump body.

Alternatively, in the case of a dry or non-lubricated pump the cooling fluid or lubricating oil, as the case may be, may be drawn from a separate sump or compartment expressly provided in or suitably attached to the pump body.

The means for circulating the cooling fluid may be any convenient pumping means of the type well known in the art. Ideally however the means for circulating the cooling fluid or lubricating oil in the present invention comprises a disk or like member provided on one of the internal pump shafts and having a portion of its periphery immersed in the sump so that on rotation fluid is transfered from the sump to an intermediate reservior by a combination of fluid adhesion and centrifugal action.

The can enclosing the magnetically driven rotor on the pump shaft may be of any suitable non-ferromagnetic material such as a suitable grade of stainless steel or the like.

An embodiment of the invention will now be particularly described by way of example with reference to the accompanying drawings in which: Figure 1 is an axial side view of one end of a mechanical blower of the lubricated intermeshing vane type, and; Figure 2 is a sectional end-on view of the pump of Figure 1 taken along the line Z-Z'.

Referring firstly to Figure 2 of the drawings, this illustrates a sectional view of one end of a mechanical blower in which pumping is produced by intermeshing rotors (not shown) rotating on parallel shafts 2, 4 within a chamber embodied within the pump body 6. A typical mechanical pump of this construction is disclosed and claimed in our co-pending United Kingdom patent application No.

8 137 164.

As shown in Figure 2, shaft 2 supporting one rotor is rotated by way of suitable geating by drive shaft 4 which supports the co-operating intermeshing rotor and which extends through and beyond the end wall 8, of pump body 6. In accordance with common practice, shaft 4 extends through the pump body end wall 8 by way of a suitable shaft seal and support bearings.

As illustrated more clearly in Figure 1, the stub end of the drive shaft 4 is conventionally secured to a squirrel cage rotor indicated generally at 10 and of the type well known in the art of magnetic drive coupling. The squirrel cage 10, is in this embodiment of the invention, adapted to be magnetically coupled to a permanent magnet member (not shown) of high magnetic coercivity which is connected to a prime mover effective, when energised, to produce operation of the pump.

In order to provide effective sealing of the pump, and in particular to prevent leakage of gas through the bearings and shaft seals supporting shaft 4, the squirrel cage rotor 10 is enclosed within a non-ferromagnetic can 11 or like enclosure, interposed between the cage and the permanent magnet forming the drive coupling. The can which may be of any non-ferromagnetic material is, in this embodiment of the invention, of a suitable grade of stainless steel displaying substantially zero magnetic permeability.

Attached to the axially inner end of the squirrel cage 10 is a radially inwardly extending and circumferentially continuous lip 12 which is effective to produce a channel from which cooling fluid, in this embodiment, pump lubricating oil, can be circulated to the radially inner surface of the cage by way of a circumferential array of spaced ducts 14 provided on the cage end-face.

Lubricating oil derived from a sump 16 provided at the base of the pump body 6, is drawn upwardly by fluid adhesion to a disk 18 secured to rotate with the pump shaft 2 and having its rim emmersed in the sump oil. Rotation of disk 18 accordingly draws lubricating oil from the sump and centrifugaly throws the oil into a receiver formed by a cut away and stationary annulus 20. Annulus 20 has one end secured to the pump body and has its other open end arranged to overlap the lip 12 provided on the squirrel cage 10.

Lubricating oil deposited into the receiver 20 is decanted into the channel formed by the lip 12 and will circulate across the inner surface of the cage by way of ducts 14. In operation of the pump, this oil will return to the sump 16 through the gap between the squirrel cage outer surface and the sealing can 11 and will accordingly extract heat from both cage surfaces to reduce excessive rise in tem erature.

As shown more clearly in Figure 2, a water cooled heat exchanger 22 is provided at the base of the sump in the pump body in order to extract excess heat imput from the lubricating oil in contact with the squirrel cage 10 and in order to maintain the body of the pump 6 at an acceptable temperature.

It will be appreciated that while the present invention has been described with reference to an oil lubricated blower it is equally applicable to other lubricated and non-lubricated mechanical pumps, such as vacuum pumps, provided with magnetic drive coupling. As hereinbefore cited, in the case of non-lubricated pumps an independent flow of lubricating or cooling fluid may be provided through a suitable heat exchange circuit embodied in or provided independently of the pump body.

It will also be appreciated that while the invention has been described with a particular form of pump providing circulation of lubricating oil, alternative forms of pump providing for cooling fluid flow may be used.

Claims (15)

1. A mechanical pump having its drive shaft terminating in a drive rotor adapted to be magnetically coupled to a co-operating member connected to a prime mover effective to produce rotation of the drive shaft, the rotor being enclosed within a non-ferromagnetic cap which is sealed to the body of the pump adjacent the drive shaft, fluid transfer means being provided to bring cooling fluid into heat exchange relationship with the rotor whereby in use to reduce its rise in temperature.

2. A pump as claimed in Claim 1, wherein the fluid transfer means are arranged to bring the cooling fluid into direct contact with the drive rotor.

3. A pump as claimed in Claim 1 or Claim 2, wherein a sump is provided as a reservoir for the cooling fluid.

4. A pump as claimed in Claim 3, wherein the sump is a conventional sump provided on the pump for retaining lubricating fluid which acts as the cooling fluid.

5. A pump as claimed in Claim 3, wherein an independent sump is provided for the cooling fluid.

6. A pump as claimed in Claim 4 or Claim 5, wherein the fluid transfer means are arranged to raise fluid from the sump into heat exchange with the rotor.

7. A pump as claimed in any one of Claims 4 to 6, wherein the fluid transfer means comprise a disc secured to the rotor and having a sector immersed within fluid in the sump, whereby to transfer fluid from the sump and onto the rotor during rotation.

8. A pump as claimed in any preceding Claims, wherein the rotor is a dished rotor and is adapted to receive cooling fluid flow over its internal surface.

9. A pump as claimed in any preceding Claim, wherein, the rotor is a squirrel cage rotor.

10. A pump as derived in any preceding claim, wherein cooling means are provided for reducing the temperature of the fluid.

11. A pump as claimed in Claim 10, wherein the cooling means comprise a heat exchanger provided within the sump for the fluid.

12. A pump as claimed in Claim 11, wherein the heat exchanger comprises water cooled tubing immersed in the fluid within the sump.

13. A pump substantially as herein described with reference to the accompanying drawings.

14. A pump substantially as shown in and adapted to operate substantially as herein described with reference to the accompanying drawings.

15. A pump unit including a pump as claimed in any preceding claim.