GB2225062A - Dampening pressure shocks in pump outlets - Google Patents

Abstract

The dampener 10 comprises a one-way valve 12 operable in response to a drop in pressure at the pump outlet 14 to introduce compressible gas into the pump fluid 16. The compressible gas absorbs shocks caused by the drop in pressure and the resultant back flow of fluid. The pumped fluid including any shock absorbing gas passes from 16 through a one- way valve 20 into a reservoir 22 where the liquid and gas separate out. The liquid passes out of the reservoir through an outlet 18 and the gas is recirculated through a pipe 28 to the valve 12. Gas losses can be replenished through a valve 32. <IMAGE>

Description

Pump Dampener The present invention relates to dampeners for use downstream of fluid pumps, and in particular, but not exclusively to dampeners for use downstream of peristaltic pumps.

Peristaltic pumps act by applying pressure to a tube containing the fluid to be pumped, thereby squeezing and closing the tube at a point along its length. The point of application of pressure is moved along the tube, thereby forcing the contents of the tube to move. The pump normally comprises a pump body which holds the tube in a "U" shape, with both the delivery and suction ends pointing in generally the same direction. Within the U, e rotating member carries two or more shoes which press on the tube to provide the necessary squeezing action. The components of the pumps are exposed to considerable forces during use especially during heavy duty use in which delivery pressures up to 15 bar may be experienced.

Previous attempts to avoid damage to the pumps have consisted of manufacturing the components from very heavy and strong materials, and designing bearings and shafts to be strong in order to withstand these forces.

The present invention seeks to reduce the forces experieticed by a pump thereby allowiiog pumps to be used for heavier duty purposes thais hitherto.

Accorditig to the iiiveiitior there is provided a dampener for use downstream of a fluid pump alid comprising means operable i in response to a drop ill pressure at the pump outlet to introduce compressible gas into the pumped fluid thereby to absorb shocks caused by the drop in pressure.

The compressible gas may be ilitroduced at a pressure equal to the pressure at the pump outlet before the sensed drop. The gas introduetion means may comprise an entry one-way valve connected between a supply of compressible gas and the pressurised fluid. The dampericr may further comprise all exit one-way valve downstream of the pump outlet and through which the pumped fluid may pass.The gas illtroductioll means may sense pressure drops ill pumped fluid between the pump outlet and the exit one-wcen valve and introduce compressible gas between the pump outlet and the exit one-way valve.

Preferably the outlet of the exit one-way valve supplies fluid to a reservoir with all outlet for the pumped fluid. Ill use, the reservoir may contain compressible gas for ilitroductiorl into the pumped fluid by the gas introduction means. The outlct of the exit one-way valve ill the reservoir is preferably above the level of the reservoir outlet for pumped fluid, whereby to assist the separatiorl of pumped fluid entering the reservoir arod compressible gas carried with it. The outlet of the exit one-way valve is preferably located relatively low in the reservoir.The outlet of the exit one-way valve preferably faces generally upwardly, and may be formed by a conduit which enters the reservoir geioeral 1 y horizontally arod t urros upwardly to form a generally upwardly directed outlet.

The reservoir may contain a gas outlet for supplying the gas introduction means, the gas outlet being relatively high ill the reservoir al1d comprising a coroduit for conducting gas to the gas introduction mcaris.

The reservoir preferably further comprises mesons for replenishing the compressible gas therein The or each one-way valve may be a beak-type valve.

The invention arises from an appreciation of the origin of the forces which affect a peristaltic pump.

A peristaltic hose roormal ly occupies a "U" shape it a peristaltic pump and is thereforesubject to tension forces in its outer surface and -compressive forces at its inner surface. These forces cause the tube to flatten slightly so that the capacity of a length of tube slightly reduces from the capacity of the tube when straight and of circular cross-section.

Fluid moving through the pump is initially at a relatively low pump inlet pressure, or suction pressure.

The fluid will remain at this pressure while moving through the pump, between two shoes. Eventually, the fluid approaches the pump outlet and the downstream shoe begins to release its pressure on the tube. This exposes the fluid to the full pressure at the pump outlet in the tube downstream of the pump. The pressure difference, which can be large in some situations, causes a reversal of the fluid flow direction at the outlet as fluid returns into the pump to equalize the pressures and to inflate the tube to its round cross-section under outlet pressur,e. This reversal of the flow direction causes shock waves within the fluid which travel at sonic velocities and exert potentially damaging forces on the pump components until absorbed by the components.

In accordance with the invention, these forces can be absorbed by the compressible gas introduced into the pumped fluid, thereby reducing or eliminating damage to the pump itself. Liquid being pumped is virtually incompressible, and so makes little contribution to absorbing shock. A gas will be significantly more compressible and absorbent.

One embodiment of a dampener according to the present invention will now be described in more detail, by way of example only and with reference to the accompanying drawing which is a schematic diagram of a dampener according to the invention.

The dampener 10 is for use downstream of a fluid pump (not shown) and comprises means 12 in the form of a valve operable in response to a drop in pressure at the pump outlet 14 to introduce compressible gas into the pumped fluid at 16. The compressible gas absorbs shocks caused by the drop in pressure and the resultant back flow of fluid.

In more detail, the dampener inlet is formed by or is connected to the pump outlet 14. Fluid pumped through the dampener 10 leaves through an outlet 18. Between the inlet 14 and outlet 18, the fluid passes through a second valve 20 and a reservoir 22.

The valve 20 is a one-way self-closing valve such as a beak-type valve moulded in rubber. The outlet of the valve 20 is in the form of a tube or pipe 24 which enters the reservoir 22 near the bottom of the reservoir and then turns upwardly. The outlet end of the pipe at 26 is accordingly generally upwardly directed and is also above the level of the outlet 18.

The valve 12 is also a one-way valve connected with its outlet between the dampener inlet 14 and the valve 20. The inlet end of the valve 12 is connected through a pipe 28 to the top of the reservoir 22, above the level of liquid 30 in the reservoir. The reservoir 22 and pipe 28 are filled with compressible gas between the upper surface of the liquid 30 and the valve 12. This gas, which may be air, can be replenished in case of loss through a valve 32 supplied for instance from a compressed air line (not shown).

The dampener operates in the following manner.

Normally during use, the pressure within the dampener will stabilize at the pump outlet pressure which in turn will be the outlet pressure at the dampener outlet 18.

Fluid (normally liquid) pumped in through the inlet 14 passes through the valve 20 into the reservoir 22 and vents from the outlet 18. The compressible gas in the pipe 28 will be at pump outlet pressure so that the valve 12 remains closed.

In the event of any drop in pressure at the inlet 14, which may be caused for instance by a shoe leaving the tube of a peristaltic pump, liquid is prevented from returning from the reservoir 22 by the valve 20. A pressure difference is now present across the valve 12 and this causes the valve to open to release compressible gas into the pumped fluid between the inlet 14 and the valve 20, until the pressures are equalized and the valve 12 closes. The presence of gas in the pumped fluid at this point causes shock waves in the liquid to be absorbed by the gas. They are dissipated much more quickly than they would be dissipated in a liquid-filled tube, so that the potential for damage to the pump is reduced.In the absence of compressible gas, the shock waves would travel along the tube, being reflected many times from obstructions such as the valves, until eventually being absorbed by the components of the pump or the dampener.

Once the pressures have equalized and the shock waves have been dissipated, pumping continues so that the liquid containing the compressible gas is pumped through the valve 20 into the reservoir 22. Within the reservoir, the gas and liquid tend to separate out. This separation is encouraged by the upward direction of the outlet 26.

The location of this outlet above the outlet 18 reduces the likelihood of gas leavirlg the outlet 18. However, it is expected that some loss of gas will normally occur during use. The valve 32 is used to compensate for this.

The valve 32 may be open regularly or in respottse to a sensor detecting an abnormally low volume of gas within the reservoir 22.

Variations may be made to the apparatus described above without departing from the spirit atid scope of the present i rivettti or'. Ill particular, di fferettt valve designs and types may be used artd other layouts of outlet attd outlet to the reservoir may be appropriate ill some circumstances. Ill some layouts, valves correspottdittg to the valves described may tot be required. Compressible gases other than air may be used.

Claims (18)

1. A dampener for use downstream of a fluid pump arid comprising means operable ill response to a drop itt pressure at the pump outlet to introduce compressible gas into the pumped fluid thereby to absorb shocks caused by the drop in pressure.

2. A dampener according to claim 1, ill which the compressible gas is irttroduced at a pressure equal to the pressure at the pump outlet be fore the sensed drop.

3. A dampener according to claim 1 or claim 2, itt which the gas introduction means comprises an entry one-way valve connected betwcen a supply of compressible gas arid the pressurised fluid.

4. A dampener according to arty of claims 1 to 3, comprising all exit one-way valve dowristream of the pump outlet rid through which the pumped fluid may pass.

5. A dampener according to claim 4 whelp dependent ort claim 3, itt which the gas introduction me arts senses pressure drops in pumped fluid between, the pump outlet and the exit one-way valve arid introduces compressible gas between the pump outlet arid the exit orie-way valve.

6. A dampener according to claim 4 or 5, in which the outlet of the exit one-way valve supplies fluid to a reservoir with an outlet for the pumped fluid.

7. A dampener according to claim 6, iri which ill use, the reservoir contains compressible gas for introduction iiito the pumped fluid by the gas introduction means.

8. A dampener according to claim 7, in which the outlet of the exit one-way valve faces general 1 y upwardly.

9. A dampener according to claim 8, ill which the outlet of the exit one-way valve is formed by a conduit which enters the reservoir generally horizontally and turns upwardly to form a generally upwardly directed outlet.

10. A dampener according to arty of claims 7 to 9, itt which the outlet of the exit one-way valve in the reservoir is above the level of the reservoir outlet for pumped fluid, whereby to assist the separation of pumped fluid entering the reservoir and compressible gas carried with it.

11. A dampener according to arty of claims 6 to 10, ill which the outlet of the exit one-way valve is preferably located relatively low ill the reservoir.

12. A dampener according to ally of claims 6 to 11, ii which the reservoir corttai ris a gas out let for supplying the gas introduction means.

13. A damperter according to claim 12, in which the gas outlet is relatively high itt the reservoir arid comprises a cortdui t for collductiog gas to the gas introduction means.

14. A dampener according to claim 12 or claim 13, ill which the reservoir comprises means for replenishing the compressible gas therein.

15. A dampener according to ally of claims 4 to 14 when dependent ott claim 3, itt which the entry one-way valve is a beak-type valve.

16. A dampener according to arty of claims 5 to 15 whet dependent ott claim 4, in which the exit one-way valve is a beak-typE valve.

17. A dampener for use downstream of a fluid pump substantially as hereinbefore deseribed with reference to the accompanying drawing.

18. Ally novel subject matter or combination ineluding novel subject matter disclosed in the forcgoing specification or claims and/or shown in the drawings, whether or not within the scope of or relatirig to the same invention as any of the preceding claims.