GB2150647A - Pump adapted to avoid damage being caused by a blockage in the pump chamber - Google Patents

Abstract

The pump comprises a pump chamber 18 defined by a lower housing 24 and a delivery chamber 20 in an upper housing 26. The chambers 18, 20 are separated by a diaphragm 22 of which the edge can move into and out of abutment with the rim of the lower housing 24. The lower housing 24 is detachably mounted on an upper housing 26 and a reciprocating drive is provided through the upper housing from an eccentric 29 to the centre of the diaphragm 22 and through an intermediate member 64, a compression spring 32 and a drive member 68. On the down- stroke the drive is transmitted through the spring whereas on the up-stroke the drive is positive and by way of a pin 78 abutting the upper ends of slots 80 in the drive member 68. If an obstruction should occur in the pump chamber 18 the shock of impacts between the obstruction and the diaphragm or its fittings is absorbed by the spring. <IMAGE>

Description

SPECIFICATION Pump adapted to avoid damage being caused by a blockage in the pump chamber The present invention relates to pumps of the type having a pump chamber and a delivery chamber communicating respectively with inlet and outlet ports, a non-return valve allowing flow from the pump chamber to the delivery chamber, and means for changing the volumes of the chambers simultaneously and in opposite senses. A drive mechanism applies a reciprocating drive to the volume-changing means cylically changing the volume of the chambers and hence producing a pumping action.

On one stroke of the pump the pumped medium is forced from the pump chamber to the delivery chamber through the non-return valve. On the return stroke the pumped medium is expelled from the delivery chamber through the outlet port and further pumped medium is drawn into the pump chamber through the inlet port.

The reciprocating drive to the volumechanging means is commonly provided from an engine through an eccentric drive.

A principal cause of breakdowns in pumps of this type is the presence of an obstruction in the pump chamber. An obstruction can occur when a pump is pumping liquid containing solids, and may cause considerable damage to the drive mechanism when the pump chamber volume is decreasing. The obstruction may be a large solid which enters the pump because a filter has not been fitted in the pump inlet, or an accumulation of silt in the pump chamber.

In an attempt to overcome this problem, it is common to use a shear pin in the drive mechanism to couple the output shaft of the engine to the input shaft of the eccentric drive from which the volume-changing means are driven. The shear pin breaks when the torque being transmitted increases above a value determined by the strength of the shear pin.

However, in practice, it is difficult to determine how strong the shear pin should be, because the torque at the shear pin resulting from an obstruction in the pump chamber varies according to the position of the eccentric drive at the moment when thc obstruction is hit. If the drive is in its midstroke position, the shearing force applied to the shear pin in the presence of an obstruction is much greater than when the drive is at or near the bottom of its stroke. Accordingly, the force which must be borne by other elements of the drive mechanism before the shear pin breaks, and hence the likelihood of damage occurring to these elements, depends on the point in the cycle at which the obstruction is hit.

Moreover, when a shear pin does break, a workman will often replace it with anything available which can serve to reconnect the drive, so that the pump can continue being used. The shear pin may even be replaced without the obstruction being cleared. This is particularly likely to happen if the pump chamber cannot easily be opened and cleared.

If the pump is restarted without the obstruction having been cleared, and with a makeshift shear pin in the drive mechanism, further, serious damage to the pump may result.

The present invention provides a pump having a pump chamber and a delivery chamber communicating respectively with inlet and outlet ports, non-return valve means allowing flow from the pump chamber to the delivery chamber, means for changing the volumes of the chambers simultaneously and in opposite senses, and drive means comprising a resilient member and applying, in use, a reciprocating drive to the volume-changing means, cyclically to change the chamber volumes, the drive being transmitted respectively through the resilient member and positively when the pump chamber volume is decreasing and increasing.

A shock to the drive mechanism of a pump according to the present invention, caused by an obstruction in the pump chamber, is absorbed by the resilient member, without damaging the drive mechanism. The presence of an obstruction becomes apparent from a reduction in the pump output, because of the limitation on the usable volume of the pump chamber. This reduction in output (which will be gradual in the case of silting up), will eventually alert a workman to the problem, although an unattended pump can continue working without damage.

The invention is particularly appiicable to diaphragm pumps, in which the volumechanging means comprises a flexible diaphragm forming all or part of a boundary between the chambers.

Diaphragm pumps are used, for instance, on building sites for pumping water to keep trenches and ditches dry. They are well suited to such environments because they can be of a construction which is mechanically simple and rugged. Although the output of most available diaphragm pumps is modest, they have the advantages of being able to pump water containing solids of many sorts and, if neglected, can run dry for long periods of time without damage.

Preferably, at least part of the periphery of the diaphragm is free to move into and out of abutment with a valve seating to form therewith the said non-return valve means. This arrangement is mechanically simple and provides for simple maintenance, since the diaphragm of a pump is normally changed regularly, and this operation simultaneously renews the valve member of the non-return valve means.

Preferably, the diaphragm is in the roof of the pump chamber and the floor of the deliv ery chamber.

With this arrangement, the down stroke of the diaphragm only serves to transfer fluid from the pump chamber to the delivery chamber, so that only a small force must be delivered to the diaphragm during this stroke.

Moreoever, the force required is independent of the situation in which the pump is being used, and in particular, it is independent of the height to which the pump is pumping fluid. Accordingly, a strong, bulky spring is not required even when pumping to a great height. The strength of the spring is chosen with regard to the other design parameters of the pump, for instance the flexibility of the diaphragm. Once chosen in this way, the spring need not be changed, whatever the use to which the pump is put.

On the up stroke of the diaphragm, the force required to pump fluid out of the outlet port does depend on the height to which the pump is pumping fluid. However, since the drive from the engine to the diaphragm is positive during this stroke rather than being transmitted through the spring, the full power of the engine is available to provide this force.

Preferably, the drive means comprises first and second rigid members slidably connected, and the drive to the volume-changing means is transmitted from the first rigid member to the second rigid member through the said resilient member, when the volume of the pump chamber is decreasing. The resilient member may be arranged to urge the first and second rigid members to a first extreme relative position, and in the stop means comprising a face of the first rigid member and a face of the sccond rigid member, the said faces being so oriented that they abut when the first and second rigid members are in the first extreme relative position. Preferably, one of the rigid members is slidable in a bore in the other rigid member, and comprises a pin carried by the said one rigid member and running in a slot or recess in the wall of the bore.This arrangement allows the invention to be embodied in a drive mechanism without the mechanism being unacceptably bulkier than known drive mechanisms. The resilient member is preferably a spring acting between the said one rigid member and an end wall of the said bore.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a view in elevation of a pump embodying the invention; and Figure 2 is a section of part of Figure 1 viewed from the other side.

The drawings show a pump 10 powered by a petrol or diesel engine 1 2. The pump 10 is for delivering water from an inlet hose 14 to an outlet port 1 6 and is a diaphragm pump comprising a pump chamber 18 and a delivery chamber 20, each bounded partly by a flexible diaphragm 22 and partly by a lower housing 24 and an upper housing 26, respectively. A drive mechanism for applying a reciprocating drive to the central region of the diaphragm 22 comprises a chain reduction unit at 28 between an eccentric at 29 and an output shaft 30 from a reduction gearbox driven by the engine 1 2. The eccentric is coupled to the central region of the diaphragm through a coupling including a resilient member in the form of a compression spring 32.On the down-stroke to the diaphragm 22, that is when the volume of the pump chamber 1 8 is being decreased, the drive is transmitted through the spring 32. On the up-stroke the drive is positive as will be described later.

The pump is mounted on a generally rectangular base 34 which has a leg 36 at each corner. A handle 38 and a pair of wheeis 40, only one of which is shown, allow the pump to be moved easily.

In Figure 2 the pump inlet port 42 communicates with the pump chamber 1 8 through a non-return valve 44, for instance a clack valve, which allows fluid flow from the inlet port into the pump chamber 1 8. The exit port communicates directly with the delivery chamber 20 in the upper housing 26, above the diaphragm 22. The diaphragm 22 is a circular, flexible, resilient disc supported at its centre, and shown resting around its edge on a rim 46 of the lower housing 24. The diaphragm 22 may be a rubber or neoprene disc and is free to move upwardly off the rim 46. Reciprocation of the centre of the diaphragm 22 generates a pumping action in the following way.On a down stroke of the centre of the diaphragm 22, fluid in the pump chamber 18 is prevented from leaving the chamber 18 through the inlet port 42 by the clack valve 44, and so forces the diaphragm 22 off the rim 46 and some fluid enters the delivery chamber 20. The diaphragm 22 and the rim 46 act as a non-return valve, so that on the up stroke of the centre of the diaphragm, some of the fluid in the delivery chamber 20 is pumped out of the outlet port 16, while more fluid is drawn into the pump chamber 18 from the inlet port 42.

As described above, the drive from the engine 1 2 is transmitted through a reduction gearbox to the shaft 30. The reduction gearbox gives as reduction of 6:1. The drive from the shaft 30 is transmitted through a chain reduction unit in the housing 28. This gives a further reduction of 4:1 and drives a drive shaft 48 of an eccentric 29. The drive shaft 48 is mounted in two bearings 52 and carries an eccentric circular cam 54 shown at midstroke in Figure 2.

A connecting rod 56 comprises a circular collar at its upper end, and an arm 56a at its lower end which carries a cross pin 58. The eccentric cam 54 drives the connecting rod 56 through a ball race 60 located between the cam 54 and the collar of the rod 56. The ends of the pin 58 are received in, and are free to turn in sockets 62 in respective vertical limbs of an intermediate member 64, which is constrained to be movable along the axis of the tubular housing portion 66. Thus the motion of the cam is converted into linear reciprocating motion of the intermediate member 64.

A final drive member 68 is movable along the axis of the housing portion 66 and comprises an upper tubular portion 68a. The diaphragm 22 is mounted on the lower end of the final drive member 68 by means of upper and lower rigid discs 72, a threaded extension 74 of the member 68 and two nuts 76.

The ends of a second cross pin 78 at the lower end of the intermediate member 64 are movable in respective slots 80 in the wall of the tubular portipn 68a of the final drive member 68. The slots 80 run parallel to the axis of the housing portion 66. The compression spring 32 acts between the bottom of the bore in the tubular portion 68a and the lower end of the intermediate member 68. The spring is preloaded to urge the intermediate member 64 upwardly with respect to the final drive member 68, to the position shown, in which the ends of the pin 78 abut the top edges of the slots 80.

The spring 32 provides a resilient and yielding connection between the intermediate and final drive members 64 and 68. The pin 78 cooperates with the ends of the slots 80 to serve as stops which limit the movement of the final drive member relative to the intermediate member.

In normal use of the pump, the spring 32 holds the intermediate member 64 and the final drive member 68 in the relative position shown with the pin 78 abutting the upper ends of the slots 80 and the reciprocating motion of the intermediate member is transmitted to the diaphragm 22. However, in the event of an obstruction blocking the pump chamber 18, the spring 32 yields, allowing the pin 78 to move in the slots 80. Thus the spring absorbs the shock of the impact between the diaphragm 22 (or the nuts 76) and the obstruction, and allows the intermediate member 64 to move with the normal amplitude. On the up stroke of the member 64, the pin 78 moves back into abutment with the top of the slots 80, to provide a positive drive to the diaphragm.

Bushes 82 are provided between the intermediate member 64, and between the final drive member 68 and the housing portion 66.

The bushes are pre-packed with grease during manufacture and are designed to run without further lubrication. Gland packing 84 prevents water leaking into the drive mechanism from the delivery chamber. Preferably the pin 78 is a slack fit in the slots 80 to allow the members 68, 64 to align themselves. The pin 78 prevents the member 68 rotating when the nuts 76 are released to change the diaphragm.

In the pump shown, the upper housing 26 is integral with the base 34. The lower housing 24 is bolted to the underside of the base e 34 by four bolts (not shown) and a ring 86 seals the join. The bolts allow the allow the lower housing to be removed, to clear an obstruction in the pump chamber 1 8 or to replace the diaphragm, without any of the drive mechanism to the diaphragm being dismantled.

The housing portion 66 is nested at its lower end in a tubular extension of the upper housing 26 and at its upper end in a housing portion 88. Preferably these joints are secured with adhesive so that the integers of the drive mechanism can be machined to their final form before assembly. The cam 54 is preferably secured to the shaft 48 by adhesive.

Although the embodiment described above is a diaphragm pump, pumps of the type to which the invention relates do not necessarily incorporate a diaphragm. For instance, a piston with two faces could bound the pump chamber with one face and the delivery chamber with the other face. A by-pass passage between the chambers, and a non-return valve situated in the passage could be used to enable fluid to flow from the pump chamber to the delivery chamber, or a passage could be provided through the piston itself. a valve being situated in the passage.

Other arrangements which use diaphragms are also possible. For instance. the diaphragm 44 could be fixed around its edge, or a separate diaphragm could be used for each chamber, the two being driven in sympathy.

In each case, a by-pass passage would be provided through the housings 24, 26 and a non-return valve would be located in the passage.

The drive mechanism is shown driving the diaphragm from above, but could drive it from below. Alternatively, other mechanisms which transmit drive through a resilient member when the pump chamber volume is decreasing. and positively when the pump chamber volume is increasing, could be used.

The compression spring could be replaced by another type of spring. For instance, an extension spring could be used on the other side of the pin 78.

The sockets 62 and slots 80 are shown as openings in the walls of the members 64 and 68. Alternatively, recesses in the inwardly facing faces of the members could be used.

Claims (18)

1. A pump having a pump chamber and a delivery chamber communicating respectively with inlet and outlet ports, non-return valve means allowing flow from the pump chamber to the delivery chamber, means for changing the volumes of the chambers simultaneously and in opposite senses, and drive means comprising a resilient member and applying, in use, a reciprocating drive to the volumechanging means, cyclically to change the chamber volumes, the drive being transmitted respectively through the resilient member and positively when the pump chamber volume is decreasing and increasing.

2. A pump according to claim 1, wherein the volume-changing means comprises a flexible diaphragm forming all or part of a boundary between the chambers.

3. A pump according to claim 2, in which at least part of the periphery of the diaphragm is free to move into and out of abutment with a valve seating to form therewith the said non-return valve means.

4. A pump according to claim 2 or 3, wherein the diaphragm is in the roof of the pump chamber and the floor of the delivery chamber.

5. A pump according to any preceding claim, wherein the drive means comprises first and second rigid members slidably connected, and wherein the drive to the volume-changing means is transmitted from the first rigid member to the second rigid member through the said resilient member, when the volume of the pump chamber is decreasing.

6. A pump according to claim 5 in which stop means are provided to limit the movement of the first and second rigid members relative to one another in one direction, the stop means engaging during the pump cycle when the pump chamber volume is increased to provide the positive drive to the volumechanging means.

7. A pump according to claim 5 or 6, wherein the said resilient member urges the first and second rigid members to a first extreme relative position, and in which the stop means comprise a face of the first rigid member and a face of the second rigid member, the said faces being so oriented that they abut when the first and second rigid members are in the first extreme relative position.

8. A pump according to claim 5, 6 or 7, in which one of the rigid members is slidable in a bore in the other rigid member.

9. A pump according to claim 8, further comprising a lug integral with the said one rigid member and running in a slot or recess in the wall of the bore.

10. A pump according to claim 8, further comprising a pin carried by the said one rigid member and running in a slot or recess in the wall of the bore.

11. A pump according to claim 7, 8, 9 or 10, in which the resilient member is a spring acting between the said one rigid member and an end wall of the said bore.

12. A pump according to any of claims 5 to 11, further comprising an eccentric drive drivable by a rotating shaft to apply a reciprocating drive to the first rigid member.

1 3. A pump according to any preceding claim, having an inlet valve in the inlet port.

1 4. A pump according to any preceding claim, comprising first and second housings which bound, with the volume-changing means, the pump chamber and delivery chamber respectively.

15. A pump according to claim 14, wherein the reciprocating drive to the volume-changing means is through the second housing.

16. A pump according to claim 14 or 15, wherein the first housing is detachably mounted on the second housing and permits removal of an obstruction from the pump chamber without the need to dismantle any other part of the pump.

1 7. A pump according to any preceding claim, in which at least part of the drive means is housed in a further housing comprising a plurality of housing portions bonded together by an adhesive.

18. A pump substantially as described above with reference to and as shown in the accompanying drawings.