GB2071211A - Centrifugal pumps - Google Patents

Abstract

In order to prevent damage to pumps, particularly beer pumps, caused by overheating when running dry, the pump drive shaft (20) extends through a plate (16), and a fan (32) mounted on the drive shaft outside the pump chamber (10) directs air across the plate to cool it. The shaft is sealed by a carbon bush (26) biased against the plate (16) by a spring (28). <IMAGE>

Description

SPECIFICATION Pump This invention relates to a pump and more particularly a pump for dispensing liquids such as beer.

It is now common practice for beer to be dispensed in public houses by means of a pump which transports the beer from a barrel in the cellar two the point or points of dispense at the bar usually some distance away. The pump employed is usually of the kind which comprises a chamber containing an impeller mounted on a shaft, the said shaft extending through a plate to the pump motor. A seal between the shaft and the plate inside the chamber is provided by a carbon bush surrounding the shaft and urged with considerable pressure against the plate by a spring. The plate itself is surrounded by a sealing ring which makes a seal between the plate and the plastics chamber wall in which the plate is located.

Under normal operating conditions the liquid being pumped acts as a coolant for the carbon seal. When a barrel is emptied and the pump runs in a dry condition the heat generated by the friction between the carbon seal and the plate is no longer dissipated in the pumped liquid. After a very short period of dry operation of the order of 2 to 3 minutes, the heat generated is sufficient to soften the plastic chamber wall in which the plate is located. Once that occurs the pressure of the carbon seal against the plate causes the plate to move relative to the chamber wall thus breaking the seal between the plate and the chamber wall.

As a consequence when liquid is once again fed to the pump chamber it will leak from the pump chamber between the plate and the chamber wall.

The problem described above is extremely widespread since most public houses use pumps for dispensing beer and only a very short period of dry running is needed for the pump to develop a leak as aforesaid.

According to the present invention there is provided a pump for dispensing liquids comprising a pump chamber, a drive shaft extending through a plate in the charnber wall, a fan mounted on the drive shaft outside the chamber arranged such that upon rotation of the shaft an air stream is directed across the exterior of the plate to cool it.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing which is a side elevation part sectional view of a pump.

Referring to the drawing the pump comprises a pump chamber 10 having an inlet 12 and an outlet 14. The pump chamber is of plastics material with the exception of the rear wall 1 6 thereof which is of metal, for example stainless steel or porcelain. It will be noted that the metal rear wall differs from the normal rear wall construction which is of plastics surrounding a small metal plate. The wall is of relatively massive proportions so that it will dissipate heat. The surface of the wall is preferably lapped to high standard of flatness.

A bore 18 is provided in the rear wall 16 through which the drive shaft 20 extends from pump motor 22 into the pump chamber 10. An impeller 24 of known configuration is mounted on the shaft 20 in the chamber 10. A carbon bash 26 surrounds the shaft 20 and is urged against the rear wall 1 6 by a compression spring 28 which bears at one end against the impeller 24 and at the other end against a metal cup 30 in which the bush 26 is seated. The pressure by which the bush 26 is urged against wall 1 6 is preferably not very much greater than that required to obtain a seal around the shaft 20.

A fan 32 is mounted on the shaft 20 between the rear wall 1 6 and the pump motor 22. A cowling 34 comprising an open ended cylindrical body with an internal baffle 36 is mounted on the pump chamber so that the baffle is disposed between the chamber and the fan. The arrangement of fan 32 and cowling 34 is to create, upon rotation of the shaft 20 a stream of air which passes in the direction of the arrows 40 across the back of the metal rear wall 1 6. The effect of the air stream, which of course is created whenever the pump operates, is to cool the rear wall 1 6. This cooling is adequate to remove sufficient heat generated by friction between the carbon bush 26 and the rear wall 16 if the pump runs dry, to prevent any softening of the plastics pump chamber adjacent the metal part thereof.

It has been noticed that after operation of the pump, to dispense liquids containing dissolved gases, such as beer, particularly at high speeds, a relatively large bubble of gas forms in the chamber and floats upwardly into the chamber outlet.

Careful observation revealed that a low pressure region develops on the front face of the pump impeller. With continued operation of the pump the pressure in the region falls until a vacuum is formed. The volume occupied by the low pressure or vacuum region continues to grow, rather like a nose from the centre of the pump impeller and into the chamber inlet. When the pump stops the vacuum region is filled at least in part with gas coming out of solution in the liquid being dispersed.

In order to prevent the development of a vacuum aforesaid a vacuum spoiler in the form of an elongate dome 42 is provided on the front face of the impeller 24 and co-axial therewith. The dimensions of the dome are selected so that it will occupy the region in which a vacuum is likely to develop.

In addition to dealing with the problems of dry running of the pump the cooling effect of the air stream during normal operation reduces the heat that in prior art pumps is picked up by the liquid being pumped. That heat, when the liquid is beer causes dissolved gas to be released which is undesirable. The present invention helps to maintain dissolved gas in solution.

A further problem that occurs with prior art pumps is that on dry running the plastic pipes connected to the inlet and outlet to the pump chamber may be softened. When the pump is reconnected to a supply of liquid the increased pressure (as compared with dry running) causes the aforesaid pipes to jump off the pump chamber connections with considerable waste of liquid. The cooling effected by the present invention prevents the softening of plastic pipes connected to the pump chamber should the pump run dry.

The invention is not confined to the embodiment just described but may be modified in many ways. For example the exhaust air stream may be directed across the pump motor in order to remove heat generated by the motor. The metal rear wall 16 may be formed with external ribs so as to increase the surface area and improve the heat transfer from the wall 1 6 to the air stream.

If desired a thermally controlled switch for the motor may be provided which is arranged to be actuated by temperature sensing means in the pump chamber. By such an arrangement the pump is automatically stopped if a rise in temperature is sensed for example as a consequence of starvation of liquid supply to the pump.

Claims (8)

1. A pump for dispensing liquids comprising a pump chamber, a drive shaft extending through a plate in the chamber wall, a fan mounted on the drive shaft outside the chamber arranged such that upon rotation of the shaft an air stream is directed across the exterior of the plate to cool it.

2. A pump as claimed in Claim 1, wherein a housing is provided around at least a part of the pump chamber for directing the said air stream.

3. A pump as claimed in Claim 2, wherein the housing comprises an internal baffle disposed between the chamber and the fan.

4. A pump as claimed in any preceding Claim, wherein means are provided for directing the air stream over drive means coupled to the drive shaft.

5. A pump as claimed in any preceding Claim, wherein vacuum spoiling means is provided in the pump chamber.

6. A pump as claimed in any preceding Claim, wherein the plate is of metal or porcelain.

7. A pump as claimed in any preceding Claim, wherein temperature sensitive means is provided in the pump chamber adapted to control operation of the pump.

8. A pump for dispensing liquids substantially as described herein with reference to the accompanying drawing.