GB2178796A - Detecting overheating in a pump - Google Patents

Abstract

A rotary vane pump 10 comprises a rotor 11 mounted in a housing 12 by means of a front and rear carbon end plates 25, 26. A temperature sensitive device 39 is located in a cap 45 of the housing 12 so as to contact one face of a flexible diaphragm 40 whose other face contacts the outer face 41 of the front end plate 25, thereby ensuring good thermal contact between the temperature sensitive device 39 and the front end plate 25 and hence a short response time to undesirable temperature rises in the pump 10. An aperture 42 in the front end plate 25 allows pump pressure to be transmitted to the diaphragm 40 to ensure its contact with the temperature sensitive device 39. <IMAGE>

Description

SPECIFICATION Pump This invention relates to pumps, and in particularto pumps having a rotor mounted in a body of a housing. Such pumps may be provided with means for detecting overheating thereof or excess pressure therein due to some malfunction, and on such detection for stopping the drive to the pump rotorto prevent premature failure thereof.

Overheating of a pump may be caused by a block age in orciosing ofthe outlet from the pump. In such circumstances pressure builds up in the pump outlet and a by-pass valve opens to release such pressure build up. This allows fluid to pass from the outlet back to the pump inlet, thereby setting up a fluid circulation in the pump with a consequenttemperature rise. This can lead to steam generation and excess pressure, possibly causing failure of pipes, connectionsthereof, or even bursting or melting ofthe pump body. Overheating of the pump may also be caused buy a lack of supply to the pump, leading to dry-running and subsequent heat generation due to friction and possible failure of the carbon components of the pump.

To overcome the abovementioned problems it is known to provide a temperature sensitive device in the bodyofthe pump housing and/orto provide a pressure sensitive device in the inlet to the pump.

Operational problems and cost make the lattersolution unattractive. If a temperature sensitive device is fitted in the pump body to detect a predetermined temperature, then the case of pumps having a body of metal, due to the large mass ofthe bodyandthe dissipation of heattherearound, there can be a considerabletime lag between the occurrence of the malfunction and the detection of the predetermined temperature at the location of the sensor. Alternativelythe housing body may be of a plastics material, but since such material is a relatively poor conductor of heat, again a considerable time lag can occur. Because of such time lags, which may be ofthe order of several minutes, 8 minutes being typical, the pump may be damaged, possibly irreparably, before the drive motor is switched off by the sensor.

In orderto avoid or reduce the possibility of pump damage due to overheating it has been proposed in British Patent No. 2100228 to locate a temperature sensitive device in the outlet ofthe pump. With such an arrangement time lags, orthe "reaction time" of the overheating detection arrangement, can be reduced considerably by comparsion with the previously known arrangements,forexample 2to 21/2 minutes may be achieved. However, it is still possible, with such time lags, for damageto the pump to occur.

It is an object of the present invention to provide a pump, and a malfunction detection arrangement therefor, whereby the abovementioned problems are avoided or the possibility of pump damage due to such malfunctions is reduced even furtherthan with the known arrangements.

The invention provides a pump comprising a rotor mounted for rotation in a housing by means of at least one bearing plate, and a temperature sensitive device mounted in said housing in good thermal contact with said bearing plate. Preferably a diaphragm may be located in said housing between and in good thermal contact with said bearing plate and saidtemperature sensitive device, and said diaphragm may be flexible. An aperture may extend through said bearing plate whereby pressure in the region of said rotor is communicated to a face of said diaphragm adjacent said bearing plate and remote from said temperature sensitive device.

Said temperature sensitive device may be located in a cap which is provided on said housing, and may be operative to switch off a source of electrical power to a drive motorforsaid rotor.

One embodiment of pump in accordance with the invention will now be described with reference to the accompanying drawings in which Figure lisa front elevation in section on line I-I of Figure 2 and Figure2 is a side elevation in section on line ll-ll of Figure 1.

Referring nowto the figures there is shown a rotary vane pump 10 comprising a rotor 11 rotatably mounted in a housing 12. Provided in the housing 12 are an inlet 13 and an outlet 14forthefluid to be pumped, which may be for example water. The rotor 11 comprises a shaft 15 mounted in a bearing 16 located in a back part 17 ofthe housing 12. The outer end 18 of shaft 15, which protrudes from the housing 12, is shaped to receive a pulley or gearwheel (not shown) which is driven, orto enterthe drive slot of a drive motor (notshown). Alternativelytheshaft 15 may be integral with a rotor part of a drive motor, in which case the drive motor may be located in the back part 17 ofthe housing 1 2.The other end 19 of shaft 15 isof smallerdiameterthanthe remainderand has a sleeve 20 secured thereon. The rotor sleeve 20 provides a step 21 against which a cap 22 abuts. One end of a compression spring 23 is retained in cap 22 and the other end engages a seal 24, which is provided aroundtheshaft 1 5within the back part 17 of housing 12, to prevent ingress ofthe pumped fluid to the bearing 16. The rotor sleeve 20 rotates within central bores provided in carbon front and rear end plates 25,26 which serve as addition bearingsforthe rotor 11. The rotor 11 also comprises a larger diameter part 27 of sleeve 20, which hasfour equi-angularly displaced radial slots 28 therein.Located between the end plates 25,26 is a carbon hoop ring 29 so that the rotor part 27 is totally enclosed by end plates 25,26 and hoop ring 29. Howeverthe hoop ring 29 has an eccentric bore 30 of larger diameter than the outside diameter of the rotor part 27 to provide a crescent shaped chamber 31 between the rotor part 27 and the hoop ring 29. Located within each slot 28 is a carbon vane 32 which is of equal radial extenttothe rotor part 27. A rod 33 extends between each diametrically opposed pair of vanes 32 whereby, on rotation of rotor 11 within the eccentric bore 30 of hoop ring 29, the vanes 32 are constrained to slide radially within their respective slots 28 so asto remain in contact with the wall of bore 30. The inlet 13 and outlet 14 communicate with the chamber 31 via apertures 34 provided in the hoop ring 29. If theoutlet14is blocked or is closed whilstthe pump 10 is still runn ing, the pressure created in the outlet 14 can rise sufficientlyto cause the plunger 35 located in a by-pass bore 36to move againsttheforce of a compression spring 37. This allows fluid to pass fro the outlet 14 through the aperture 38 and by-pass bore 36 to the inlet 13, creating the aforementioned fluid circulation and temperature rise in the pump 10.

To sense such temperature rise, or a temperature rise dueto dry running ofthe pump 10 ifthefluid supply is cut off, there is provided a temperaturesen- sing device 39 which is in good thermal contact with the front end plate 25 The temperature sensing device 39 is operative on sensing a predetermined temperature, for example in the range 30 C to 65,to cut off the electrical supply to the drive motorforthe shaft 15. A diaphragm 40 is located against the outer face 41 ofthefront end plate 25 so asto be in good thermal contact therewith. The diaphragm 40 is of any suitable material such as phospher bronze, although stainless steel is preferred since it is inert with respect two most liquids.The thickness of the dia phragm 40 is sufficient that it will withstand the operating pressure ofthe pump 10, and may beforex ample0.3mm.An aperture 42 provided in frontend plate 25 allows the operating pressure to be transmit ted to the face ofdiaphragm 40 adjacent the outer face 41 of front end plate 25 and remotefrom the tem perature sensing device 39. In this way the pressure within the pump 10 ensures that the diaphragm 40 is pressed against and is in good thermal contact with the temperature sensing device 39.An O-ring seal 43 is located in a peripheral step formation 44 formed in the diaphragm 40, and the seal 43 and diaphragm 40 prevent working fluid from leakingtothetem- perature sensing device 39 orfrom the pump 10. A cap 45, in which the temperature sensing device is located, is retained in the housing 12 by a circlip 46 and compresses the O-ring seal 43. This ensures that the diaphragm 40 is pressed against and is in good thermal contact with the front end plate 25 at least in the peripheral region thereof.

By means of the invention, any rise in temperature within the pump 10 is readily sensed and the "reaction time" of the device is ofthe order of 1 minute or less, i.e. considerably less than the prior art arrange ments. In consequence, damagetothe pump maybe avoided, or the risk thereof considerably reduced in comparison with the priorartarrangement.

Claims (14)

1. A pump c.omprising a rotor mounted for rotation ion a housing by means of at least one bearing plate, and atemperature sensitive device mounted in said housing in good thermal contact with said bearing plate.

2. A pump according to claim 1 fu rther compris- ing a diaphragm located in said housing between and in good thermal contact with said bearing plate and said temperature sensitive device.

3. A pump according to claim 2 wherein said diaphragm is flexible.

4. A pump according to claim 3 wherein an aperture extends through said bearing plate whereby pressure in the region of said rotor is communicatedto aface of said diaphragm adjacent said bearing plate and remote from said temperature sensitive device.

5. A pump according to any one of clai ms 1 to4 wherein said temperature sensitive device is located in a cap which is provided on said housing.

6. A pump according to any one of claims 1 to 5 wherein said temperature sensitive device is operable to switch off a source of electrical power to a drive motorforsaid rotor.

7. A pump according to claim 6wherein saidtemperature sensitive device is operable to switch off said electrical source on sensing a temperature in the range 30'Cto 65"C.

8. A pump according to any one of claims 1 to 7 being a rotary vane pump.

9. A pump according to claim 8 wherein said rotor is rotatably supported in bores in two bearing plates between which the vanes of said pump are located.

10. A pump according to claim 9 wherein said bearing plates are of carbon.

11. A pump according to claim 2 or any claim dependentthereon wherein said diaphragm is of stainless steel.

12. A pump according to claim 11 wherein said diaphragm has a thickness of substantially 0.3mm.

13. A pump according to claim 5 or any claim de pendentthereon wherein said cap abuts a ring seal located in contact with the periphery of said diaphragm.

14. A pump substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.