WATER PUMPS AND MOTORS

Abstract: A water pump or motor comprises an outer casing (1), a cylinder block (7) which is rotatably mounted within the outer casing (1) and a plurality of piston assemblies (9). Each of the piston assemblies (9) is mounted within a respective piston bore in the cylinder block and comprises a piston (41) having a piston ball end supporting a slipper (42). An angled swash plate (12) is fixed in position relative to the rotatable cylinder block (7), against which the slippers (42) are pre-loaded. Each slipper (42) fits into and is held in place on the piston ball end by a retaining cap (47). The retaining caps (47) are each held in position on their respective piston ball end by means of a retaining ring (13) which is angled at the same angle as the angled swash plate. The retaining ring (13) has a plurality of apertures therein.

Description: DESCRIPTION WATER PUMPS AND MOTORS The present invention relates to water pumps and motors, and more especially to a piston assembly for use therein. The present invention also provides a water driven power tool. A known water pump comprises an outer casing, a cylindrical cylinder block keyed to a drive shaft and a plurality of piston assemblies each mounted within a respective bore in the cylinder block. Each piston assembly comprises a piston which is slidable back and forth within its bore, and a slipper which is mounted on a ball at the end of the piston. The slippers are supported against an angled swash plate which is fixed in position relative to the rotatable cylinder block. At the other end of the cylinder block from the angled swash plate there is provided a port plate which is fixed in position relative to the rotatable cylinder block and which comprises an inlet port and an outlet port. Water to be pumped is supplied to the water pump through the inlet port and is expelled therefrom under pressure from the outlet port. In use, the cylinder block is rotatably driven by means of a prime mover connected to the drive shaft. As each piston bore passes into alignment with the inlet port water flows or is sucked into the bore, displacing the piston along the length of the bore against the angle of the swash plate. At a given point the bore passes out of alignment with the inlet port, thus closing off the bore with a quantity of water in it. As the cylinder block continues to rotate each slipper passes up the angled swash plate which forces the associated piston back against the volume of water in its respective piston bore and increases the pressure in the piston bore. At this point the piston bore passes into alignment with the outlet port and water is expelled therefrom under pressure. Thus water entering the pump at low pressure is pumped out at high pressure. The water pump described hereinabove can also function as a water motor. Water under high pressure is applied to the inlet port, which has the effect of driving each of the pistons in turn down its respective piston bore and r in turn, of turning the cylinder block and the drive shaft. It is, of course, essential to the effective operation of the water pump/motor that contact is maintained between the pistons and slippers. In one known arrangement a primary or boost pump usually supplies pressurised water to the pump suction. This has the effect of pushing each piston down the bore as it comes into suction, thus maintaining contact between the piston and slipper. This arrangment does not require any retention to be provided between the piston end and the slipper. The boost pump may be separate from the water pump or made up as a closed circuit. Either way the arrangment suffers from the disadvantage that boost pumps are expensive, complicate the circuit and increase costs. As an alternative to providing a boost pump the slipper walls can be swaged around the piston ball end to form a single unified assembly. This design requires a minimum positive head of water to be applied in the suction, otherwise the piston/slipper assembly works apart due to directional reversals at either end of the stroke. As an alternative to pressurised suction springs may be provided within the piston bores behind the pistons. In water pumps and motors springs are not a very satisfactory option due to high fatigue cycles on non-corrosive material. These non-corrosive materials are expensive. A further problem with springs is that the frictionless plastic outer sleeve usually provided around the piston reduces the spring diameter to a point where increased strain could become a problem. It is an object of the present invention to provide a piston assembly which obviates or at least substantially mitigates the problems of conventional piston assemblies. - 4 - According to a first aspect of the present invention there is provided a water pump/motor comprising an outer casing, a cylinder block which is rotatably mounted within the outer casing, a plurality 5 of piston assemblies, each of which is mounted within a respective piston bore in the cylinder block and each of which comprises a piston body having a piston ball end supporting a slipper, and an angled swash plate which is fixed in position relative to the rotatable 10 cylinder block and against which the slippers are pre¬ loaded, wherein each slipper fits into and is held in place on the piston ball end by a retaining cap and wherein the retaining caps are each held in position on their respective piston ball end by means of a 15 retaining ring having a plurality of apertures therein, each of which receives and secures a respective retaining cap, which retaining ring is angled at the same angle as the angled swash plate. Preferably the retaining cap is retained on the 20 piston ball end by means of a split ring or retaining bush which passes over.the piston ball end. Preferably the retaining cap takes the form of a so-called "top hat" - that is to say it comprises a tubular body with an outwardly extending circum- 25 ferential flange at one end. The tubular body is seated in a respective one of the said apertures in the retaining ring and is held in place by the circum¬ ferential flange. The piston ball end and the retaining bush are received in the opposite end of the tubular body from the flange; the slipper fits into the flanged end of the tubular body. Preferably the retaining ring is maintained at the same angle as the swash plate by means of a keep ring wedge. The keep ring wedge is an annular member having a wedged cross section and is fixed in position behind the annular retaining ring. Preferably a wave spring is provided behind the retaining ring which spring biases it towards the swash plate, thus pre-loading the retaining caps mounted therein and compensating for minor machining inaccuracies and limited wear between individual slippers and pistons. Such constant loading is not available with individual springs. According to a second aspect of the present invention there is provided a water driven power tool comprising a water motor. In a preferred embodiment of the second aspect of the present invention the water driven power tool comprises a drilling rig having a hollow combined bit and sprayer which is rotatably driven by the water motor, and switching means for switching water under - 6 - pressure from the water motor into the hollow combined bit and sprayer so that water under pressure sprays therefrom. Thus, in use the drilling rig can be used to drill holes in the thin metal skin of vehicles, containers, vessels, and the like and then water can be sprayed into the interior thereof through the combined bit and sprayer. Preferably, the water driven power tool is driven by a water motor in accordance with the first aspect of the present invention. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a cross sectional view through a water pump/motor according to the first aspect of the present invention? Fig. 2 shows an enlarged detail of a piston assembly suitable for use in the water pump/motor shown in Fig. 1? Fig. 3 shows a cross sectional view through a water driven power tool according to the second aspect of the present invention; Fig. 4 shows a cross section through the water driven power tool of Fig. 3 along lines I -IV to illustrate the flow regulating device; and Fig. 5 shows a cross section through the water driven power tool of Fig. 3 along lines V-V to illustrate the switching device. Referring to Fig. 1 of the accompanying drawings the water pump/motor comprises a tubular outer casing 1 which is closed at one end by a port end covering 2 and at the other by a mounting flange plate or snout 3. Bolts (not shown) hold the port end covering 2 and the mounting flange plate 3 to the outer casing 2 and 0- rings 22 seal the connections therebetween and prevent any leakage of fluid. An aperture is defined in the centre of the mounting flange plate 3, within which is mounted a drive shaft 4. The drive shaft 4 is held in place by means of a seal housing 8 which is recessed into the front face of the mounting flange plate 3 and held in place by means of socket head capscrews 26 (only one of which is shown) . The seal housing 8 also supports a seal 24 which prevents fluid leaking past the drive shaft 4, and an 0-ring 23 prevents fluid from leaking between the seal housing 8 and the mounting flange plate 3. The drive shaft 4 is rotatably supported within the aperture in the flange mounting plate 3 by means of front and rear shaft bearings 18. - 8 - Keyed to the inner end of the drive shaft 4 is a dummy shaft 36 and keyed onto the dummy shaft 36 is a cylinder block 7. The cylinder block 7 is rotatable with the drive shaft 4 within the cavity defined by the outer casing 1, port end covering 2 and flange mounting plate 3. A snout bush 16 allows free rotation of the cylinder block 7 on the inner end of the mounting flange plate 3. The cylinder block 7 carries a plurality of piston assemblies 9, only two of which are visible in the drawing. Each of the piston assemblies 9 is slidably mounted within a respective piston bore in the cylinder block 7 and as can be seen with reference to Fig. 2 of the accompanying drawings comprises a piston 41 having a ball at one end on which is mounted a slipper 42 held in place by a retaining cap 47, of the type commonly referred to as "top hat", and a split retaining bush 48. A slipper pad 45 is secured to the front of the slipper 42 by means of a screw 43 and a pump piston seat 44 supports the slipper 42 on the piston ball end. A frictionless sleeve 46 around the body of the piston 41 ensures free movement of the entire piston assembly back and forth within its respective piston bore. The inner end of the piston 41 is drilled out and leads into a capillary tube which opens in the front of piston ball end. A capillary tube is also defined in the screw 43 securing the slipper pad 45 to the slipper 42. This ensures a supply of fluid from within the piston bore to a recess or pocket provided in the front face of the slipper pad 45. This recess or pocket in the front face of each slipper pad 45 serves two purposes. The first of these is to retain a pocket of water when the pump is not in use. The second is to create a hydrodynamic film between the swash plate 12 and each piston assembly when the pump is in use which causes each slipper pad 45 to lift off the swash plate 12 into a hydrostatic balance condition as each piston sees pressure. An annular angled swash plate 12 is secured to the inner face of the flange mounting plate 3 by means of dowels 31 and it is against the swash plate 12 that the slippers 42 are supported. The angle of the swash plate 12 means that when used as a pump the uppermost piston assembly is at the beginning of its stroke within the piston bore, whilst the lowermost one is at the end. This is, of course, reversed in a motor. The slippers 42 are all pre-loaded against the angle swash plate 12 by means of a wave spring 34 which acts on the slippers 42 via a retaining ring 13 set at the same angle as the swash plate 12 by means of a keep ring wedge 33. The retaining ring 13 is annular and has a - 10 - plurality of apertures therein each of which receives a respective piston assembly. More specifically each of the apertures in the retaining ring 13 receives a respective "top hat" retaining cap 47, which in turn locates the slipper 42. The wave spring 34 is a multi¬ point contact spring which compensates for minor machining inaccuracies and limited wear between individual pistons 41 and slippers 42. With this design the piston ball remains in contact with the slipper slot throughout 360 degrees of rotation thereby retaining fluid pockets under the slipper face which would otherwise be lost due to piston inertia and slipper centrifugal effects. Each of the piston bores is open to the rear of the cylinder block 7 via a respective aperture in the end face of the said block 7. Immediately adjacent the end face of the cylinder block 7 is provided a port or timing plate 5 which is secured to the port end cover 2 by dowels 37. The port end cover 2 defines a water inlet port 52 (a low pressure port), and a water outlet port 51 (a high pressure port) , each of which is aligned with a corresponding aperture in the timing plate 5. In use a head of water is connected to the water pump via the water inlet port 52 and the drive shaft 41 is rotatably driven by a prime mover (not shown) . As the drive shaft 4 rotates the cylinder block 7 also rotates and rotates each piston assembly 9 passes in turn past the water inlet port 52. As each does water is sucked into the piston bore behind the piston 41 which is moving along the length thereof. At the end of the bore each piston assembly 9 is driven back by the angled swash plate 12 thus increasing the pressure within the cylinder bore. As the aperture connecting the cylinder bore then passes into alignment with the outlet port 51 water is expelled from the pump under pressure. It will be understood that the slippers are kept in contact with the angled swash plate 12 on the low pressure side by means of the angled retaining ring and the pre-loading effected thereon by the wave spring 34. A hydrodynamic film is thus maintained between the swash plate 12 and each of the slipper pads 45 which lubricates and allows free movement of the slipper pads 45, and hence the piston assemblies over the surface thereof. Minimal time is required to pressurise the pocket or recess in the front face of each slipper pad 45, thus reducing the initial clamping forces and thereby decreasing the stresses due to high contact loading under non-supported conditions. This reduces wear. - 12 - The snout bush 16 absorbs the reaction load from slipper forces acting at 90 degrees to the swash plate 12. As mentioned previously, a water pump may also 5 operate as a water motor. This also applies with the water pump described with reference to the accompanying drawings. All that is required is for a source of high pressure water to be connected to the outlet side of the pump. Drive is taken from the drive shaft. 10 Referring now to Fig. 3 of the accompanying drawings there is shown a water driven power tool comprising a water driven motor, generally indicated by reference numeral 51, of the type previously described hereinbefore with reference to Figs. 1 and 2 of the 1 accompanying drawings. The motor 51 is powered from a source of high pressure water (not shown) which is connected to the power tool by means of a quick release coupling 52. The high pressure water is directed to the high 20 pressure side of the motor 51 through bores in the casing of the power tool and via a switching device 53 and a flow regulating device 54 (the purpose of which will be explained later hereinbelow) . Low pressure water exiting form the motor 51 flows out of the power 25 tool through further bores in the power tool casing and a further quick release coupling 55. In use a hose is connected to the further quick release coupling 55 and low pressure water from the power tool is either returned to a reservoir associated with the source of high pressure water or conveyed to a suitable drainage point. The drive shaft 56 of the motor 51 is connected to a further drive shaft 57 via a gearbox arrangement which essentially consists of a spur gear 58 mounted on the end of the motor drive shaft 56 and a gear wheel 59 which is keyed to a rotary sleeve 60 mounted on one end of the further drive shaft 57. The drive shaft 57 is, itself located within and supported by a support sleeve or tube 61 which is secured to the front face of the power tool casing by screws 62. A rotary cutting bit 63 is secured to the end- of the drive shaft 57 extending out beyond the support sleeve 61. It will be readily understood that when the motor 51 is powered by water under pressure the drive shaft 56 is caused to rotate. This, in turn, causes the drive shaft 57 to rotate within the support sleeve 61 and rotates the rotary cutting bit 63 secured to the end thereof. The operation of the rotary cutting bit 63 is controlled by the flow regulating device 54 located in the bore through which water under pressure is conveyed to the motor 51. The flow regulating device 54 is - 14 - shown in detail in Fig. 4 and comprises a valve arrangement 65 which is opened and closed by means of a valve operating shaft 66. The valve operating shaft 66 is, itself mounted within and connected to a housing defining the left hand side handle 81 of the power tool. By twisting the handle about its central axis the valve arrangement 65 is closed or opened thereby controlling the operation of the motor 51 and thence the rotary cutting bit 63. The valve arrangement 65 may operate as a switch which is either fully open to turn on the motor 51 or fully closed to turn off the motor 51. Alternatively it may be adjustable between a fully open position and a fully closed position so that the flow of water to the motor 51 is adjustable. This enables the speed of the motor 51, and hence of the rotary cutting bit 63 to be regulated. As shown in Fig. 3 of the accompanying drawings a hole 82 is bored in the drive shaft 57 from the end thereof supported within the power tool casing to a point just beyond the end of the support sleeve 61. At this latter end radially extending holes 83 are drilled through the sides of the drive shaft 57 to a link with the bore hole 82. Immediately beyond these radially extending holes 83 the diameter of the drive shaft 57 is increased slightly to define a lip 84 and between this lip 84 and the end of the support sleeve 61 there is retained, on the drive shaft 57 a spray sleeve or collar 67. The spray sleeve 67 has a ring of holes (not shown) drilled. in it. The bore hole running through the drive shaft 57 is continuous with a seal sleeve 68 which connects it to one side of the switching device 53. As shown in Fig. 5 the switching device 53 comprises a ball valve 69 which is connected by means of a valve operating shaft 70 the right hand side handle 71 of the power tool. The ball valve 69 lies across the high pressure water inlet to the power tool and can be switched between a first position in which high pressure water is diverted to the motor 51 (as shown in Fig. 3) and a second position in which high pressure water is diverted into the bore hole 82 running the length of the drive shaft 57. Switching the ball valve 69 between these two positions is achieved by simply turning the right hand side handle 71 about its central axis. When water under pressure is switched into the bore hole 82 in the drive shaft 57 the result is that it sprays out of the holes in the spray sleeve 67. - 16 - It will be recognised that the power tool according to the present invention provides a highly specialised yet effective piece of apparatus for introducing water under pressure into confined and 5 enclosed areas such .as vehicles, aircraft, containers, vessels and the like for the purpose of extinguishing fires. In this respect, the power tool is first switched into motor mode which causes the rotary cutting bit 63 to rotate. The rotary cutting 10 bit 63 allows a hole to be drilled in the skin or wall of the enclosed area in which the fire is contained. As soon as the rotary cutting bit 63 penetrates into the enclosed area the power tool is switched into spray mode by turning the right hand side handle of the power 1 tool. This causes high pressure water to be switched from the motor 51 into the drive shaft 57. Under high pressure water sprays out of the spray sleeve 67, thus extinguishing the fire within the enclosed area.

Claims: CLAIMS 1. A water pump or motor comprising an outer casing, a cylinder block which is rotatably mounted within the outer casing, a plurality of piston assemblies, each of which is mounted within a respective piston bore in the cylinder block and each of which comprises a piston body having a piston ball end supporting a slipper, and an angled swash plate which is fixed in position relative to the rotatable cylinder block and against which the slippers are pre- loaded, wherein each slipper fits into and is held in place on the piston ball end by a retaining cap and wherein the retaining caps are each held in position on their respective piston ball end by means of a retaining ring having a plurality of apertures therein, each of which receives and secures a respective retaining cap, which retaining ring is angled at the same angle as the angled swash plate. 2. A water motor or pump according to claim 1, wherein the retaining cap is retained on the piston ball end by means of a split ring or retaining bush which passes over the piston ball end. 3. A water motor or pump according to claim 1 or 2, wherein the retaining cap comprises a tubular body with an outwardly extending circumferential flange at - 18 - one end and the said tubular body is seated in a respective one of the said apertures in the retaining ring and is held in place by the said circumferential flange; the piston ball end and the retaining bush are 5 received in the opposite end of the tubular body from the flange; the slipper fits into the flanged end of the tubular body. 4. A water pump or motor according to claim 1, 2 or 3, wherein the retaining ring is maintained at the 10 same angle as the swash plate by means of a keep ring wedge. 5. A water pump or motor according to claim 4, wherein the keep ring wedge is an annular member having a wedged cross section and is fixed in position behind 15 the annular retaining ring. 6. A water pump or motor according to any preceding claim, wherein a wave spring is provided behind the retaining ring which spring biases it towards the swash plate, thus pre-loading the retaining 20 caps mounted therein. 7. A water driven power tool comprising a water motor. 8. A water driven power tool according to claim 7 comprising a drilling rig having a hollow combined bit 25 and sprayer which is rotatably driven by the water motor, and switching means for switching water under pressure from the water motor into the hollow combined bit and sprayer so that water under pressure sprays out therefrom. 9. A water driven power tool according to claim 7 or 8, comprising a water motor according to any one of claims 1 to 6.

Inventors: SEABROOK COLIN, SEABROOK, COLIN
Applicants: FENNER CO LTD J H, J.H. FENNER & CO. LIMITED
Application year: 1992
Main classification: F04B1
IPC codes: F04B1