NZ240660A - Double chamber reciprocating pump for slurries - Google Patents

Description

Z 4 0.6 6 0 JAMES & WELLS PATENTS FORM NO. 5 Fee No. 4: $260.00 PATENTS ACT 1953 COMPLETE SPECIFICATION After Provisional No: 240660 Dated: 19th November 1991 A PUMP I Ian Douglas De Mey, a New Zealand citizen f Panmure, Auckland, New Zealand hereby declare the invention for which I pray that a patent may be granted to me, and the method by which it is to be performed to be particularly described in and by the following statement: ' ^ 7 NOV 1992 n j *■ of 47 Ireland Road, 1 i. 4 0 6 6 0 This invention relates to a pump.

The invention may be particularly suitable as a reciprocating pump for pumping dual phase fluids such as slurries and concrete, and the present specification is therefore written with particular reference to such 5 applications. However it is to be understood that the pump is not limited to these applications and may be suitable for pumping a variety of types of fluid of both gaseous and liquid nature.

In the pumping of concrete and the like, there are several requirements of particular importance. Some of these may be listed as follows: - 1. A continuous flow. This is required so that solids do not separate out or accumulate at discontinuities such as bends, and do not tend to gravitate out to lower sections within the equipment and piping. A continuous flow also helps to maintain the homogenous nature of the mixture. Also in pouring the concrete from a nozzle which is 15 generally hand held, a continuous discharge is desirable to facilitate control and positioning of the nozzle. 2. Low vibration. Vibration of equipment and piping can cause undesirable settling out of dense material in the concrete. 3. High wear resistance of components and a minimum number of 20 moving components. This is necessary so as to minimise wear and damage in the harsh environment of water and abrasive materials. 4. Easy access for cleaning. Since concrete sets with time it is essential to be able to wash out the equipment thoroughly so that concrete does not accumulate and harden. 2 2406 . Ability to handle blockage. Concrete pumping equipment is susceptible to blockage due to the presence of stones and the like in the mixture. It is therefore necessary to be able to stop pumping in the event of blockage, and to be able to relieve the pressure to enable clearing of the blockage. 6. The ability to completely shut off flow when moving a discharge nozzle to a new location so as to prevent dripping from the nozzle. This may be achieved by reversing the pump so as to draw concrete back up the discharge pipe away from the nozzle outlet.

Various types of conventional concrete pumps are able to meet some of these requirements but each has its disadvantages.

Centrifugal pumps are able to give a relatively steady flow output. However the necessary high speed rotation of the impeller, with accompanying wear and undesirable separation of solids from the fluid, makes these pumps generally unsuitable for pumping concrete and slurries containing solid aggregate particles.

Peristaltic pumps are able to provide a relatively smooth discharge flow of fluid. However they generally have a lower efficiency due to the energy required to deform the flexible pipe section, and also the mechanism for driving the rollers is often complicated and bulky. The maximum pressure of these pumps may also be a limiting factor.

Conventional reciprocating pumps may, in certain applications, be more efficient and of a simpler construction than peristaltic pumps. However due to the reciprocating motion of the piston, the output from these pumps may have pulses. Consequently there may be undesirable settling out of solid matter, and undesirable fatigue loading of components etc. The 240660 problems with pulses in the flow may be overcome to a certain extent by providing a pump with two or more stages, wherein a part of the outlet flow from one stage may be absorbed by a second stage, while a part of the outlet flow is discharged into the pump outlet. The provision of a pulse damping 5 reservoir may also smooth out the pulses.

Conventional small to medium size reciprocating concrete pumps of this type generally consist of two or more stages arranged side by side with pistons driven in cylinders by means of a rotating crank or eccentric. With this arrangement however problems may arise due to the piston moving 10 non-linearly over its stroke. There may also be problems due to side loadings on the piston due to the oscillating connecting rod drive. This may result in uneven wear of the bore which may be pronounced in the abrasive environment of a concrete slurry.

The pulses in the outlet flow from such a pump may be minimized by 15 providing a mechanism whereby the stroke of one of the stages may be varied. This may be achieved by driving one stage with a variable eccentric drive. Such a mechanism however is inherently complicated, and due to the harsh environment and high loadings on the components, an expensive design, requiring frequent maintenance, results.

Furthermore, overloading of the pump, such as may occur in the case of downstream blockage of the discharge pipe, may not be easily sensed at the prime mover, since the pistons are driven through a crank and link mechanism having a high mechanical advantage. The design is thus susceptible to overloading in the event of blockage. It may also be difficult to 25 reverse the pump in the event of blockage to reduce pressures and loads so that the blockage may be cleared. The difficulty in reversing also makes it 4 2406 difficult to completely shut of the flow when it is desired to move the nozzle to a new location.

To minimise the vibration of such a pump it is generally necessary to use a low vibration type engine such as a petrol engine rather than a more economical but less smooth running diesel engine. In certain situations the danger of explosion of petrol may pose a significant problem.

Some of the above problems with crank or eccentric driven reciprocating type pumps may be overcome by driving the pistons in the cylinders with parallel hydraulic actuators. With this arrangement the hydraulic actuators may be operated from a remote hydraulic pump system so that a diesel engine drive may be possible. However such a system is generally expensive and bulky since a separate hydraulic actuator is generally used for each piston, and the cylinders of each stage are generally arranged side by side.

Typical systems of this type developed for pumping mud are disclosed in US patent Nos. 4,541,779, 4,611,973, 4,500,267 (Birdwell), and 5,061,159 (Pryor). These patents are related to multi cylinder, hydraulically driven dual arranged mud pumps. A non pulsating output characteristic is achieved by having adjacent pumping cylinders with one cylinder arranged so that pumping is achieved with the piston rod in tension, and the other cylinder arranged so that pumping is achieved with the piston rod in compression. The pumping sections are arranged adjacent to each other so that the equipment is bulky and difficult to manufacture and maintain.

It is an object of the present invention to provide a reciprocating pump which addresses the above problems and difficulties or at the very least offers a useful choice. 240660 Further objects and advantages of the present invention will become apparent from the ensuing description which is given by way of example.

According to one aspect of the present invention there is provided a reciprocating fluid pump comprising a first chamber and a second 5 chamber separated by a movable wall, said first and second chambers having a means for communication therebetween, said communication means comprising and/or including a first means for preventing fluid flow in one direction, wherein a displaced volume of said first chamber per unit movement of said wall is different from a displaced volume of said second 10 chamber per unit movement of said wall.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said first and second chambers are defined by walls of a first cylinder, and said movable wall is a first piston movable in said first cylinder.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said first piston is linked to an operating member which sealingly and slidingly passes through an end wall of said second chamber so that a difference in said displaced volumes per unit movement of said piston in opposite directions is dependent on a 20 cross sectional area of said operating member.

According to an alternative aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein a second cylinder of a smaller bore size than said first cylinder, and having a second piston slidable therein is arranged substantially co-axial with said first 25 cylinder, and said first and second pistons are linked together by a link means so as to reciprocate together over a part or all of their stroke within 6 2406 said first and second cylinders respectively, so that a difference in displaced volumes of said first and second chambers per unit movement of said first piston is dependent on the difference in bore sizes of said first and second cylinders.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said communication means comprises an aperture formed in said piston and said first means for preventing flow of fluid in one direction is disposed in said aperture to prevent flow of fluid from said second chamber to said first chamber.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said communication means comprises a pipe connected between said first and second chambers, and said first means for preventing flow of fluid in one direction is disposed in said pipe to prevent flow of fluid through said pipe from said second chamber to said first chamber.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said first and second cylinders are arranged so that an open end of said first cylinder communicates with an open end of said second cylinder, and said link means comprises a connecting member which passes through said open ends.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said second chamber is communicated with a discharge opening.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein another end of said first 7 2406 cylinder is provided with a second means for preventing flow of fluid in one direction.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said first means for preventing flow of fluid in one direction comprises a first non-return valve, and said second means for preventing flow of fluid in one direction comprises a second non-return valve.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein one or both of said first and second non-return valves comprises a ball valve.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said first non-return valve comprises a plunger and a seat, said plunger being fixedly connected to said connecting member, and said seat being formed in said piston such that said plunger seals against said seat when said connecting member moves in one direction, and separates from said seat when said connecting member moves in an opposite direction.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said second piston is fixedly attached to said connecting member.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said second piston is able to move relative to said connecting member over a predetermined distance.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said predetermined distance is controlled by a force on a resilient member. 8 240660 According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein a variable volume reservoir is provided which communicates with said second chamber.

According to another aspect of the present invention there is provided a 5 reciprocating fluid pump as aforesaid, wherein said variable volume reservoir comprises a piston movable in a cylinder and loaded by a resilient member.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein a means for operating said 10 reciprocating fluid pump is provided, said means comprising an actuator which is connected to said link means such that movement of said actuator is transmitted to said link means so as to move said pistons.

According to another aspect of the present invention there is provided a reciprocating fluid pump as aforesaid, wherein said actuator of said 15 operating means is operated by hydraulic pressure, or electro-magnetic forces.

According to another aspect of the present invention there is provided a method for pumping concrete comprising the steps of: drawing concrete through a means for preventing flow in one direction, 20 into a first chamber, by moving a wall disposed between said first chamber and a second chamber, and moving said wall in an opposite direction so that said concrete drawn into said first chamber is forced into said second chamber on an opposite side of said wall through a passage incorporating another means for preventing 25 flow in one direction, 9 240660 wherein a volume per unit movement of said wall in said second chamber is less than a volume per unit movement of said wall in said first chamber, so that a part of the volume of concrete forced into said second chamber is forced out of said second chamber through a discharge port.

With a re-ciprocating pump as described above, the difference in displaced volume per unit movement of said wall may be achieved by any suitable arrangement of components and designs. For example the chambers may be formed on either side of a wall which is in the form of a diaphragm or piston. The diaphragm or piston may be provided with a push rod on one 10 side thereof which moves with the diaphragm or piston and passes through a fluid tight gland in an end wall of one of the chambers. With this arrangement, the displaced volume per unit movement of the diaphragm or piston on the push rod side thereof will be less than that on the other side, due to the volume taken up by the push rod, and will be 15 dependant on the cross sectional area of the push rod. Preferably the chambers may be formed by the walls of a first cylinder and the movable wall may be in the form of a first piston which is slidable therein.

Alternatively to obtain the difference in displaced volume per unit movement of a piston, the first cylinder may be connected to a second open 20 ended cylinder of a smaller diameter than the first cylinder, and arranged substantially co-axial therewith. This second cylinder may be provided with a piston which is mounted on the push rod of the first piston so as to move with the first piston. In this case, the displaced volume per unit movement of the piston on the push rod side of the first piston will be 25 dependent on the difference between the bore diameter of the first and second cylinders, and will be less than the displaced volume per unit movement of the first piston on the opposite side of the first piston. 24066 Any suitable means may be possible for communication between the first and second chambers. This may be in the form of a non-return valve fitted to said piston to allow flow in one direction therethrough. Alternatively a pipe fitted with a non-return valve may be connected between the first and second chambers.

The first and second pistons may be connected together by a link means comprising a connecting member such as a rod. The connecting member may be fixedly attached to either or both of the pistons so that they may reciprocate together over their full strokes. Alternatively the connecting member may be linked to either or both pistons so that either or both pistons may move relative to the connecting member over a part of their stroke while still reciprocating together over the remaining part of their stroke.

In a preferred embodiment, at least one end of the connecting member may be fixedly connected to the second piston and the other end may be fixedly connected to a ball valve cage provided on the first piston. In another embodiment the connecting means may pass through an opening in the first piston, and be fitted with flanges disposed on either side of the opening, with the first piston disposed therebetween. With this arrangement the connecting member may move a predetermined amount relative to the piston and may also rotate relative to the piston. This arrangement may be adapted to provide a type of non return valve wherein one of the flanges comprises a plunger which mates with a seat on one face of the piston so that the plunger seals against the seat when the connecting member moves in one direction, and separates from the seat when the connecting member moves in an opposite direction. The piston may be moved in said opposite direction by the other flange which may be separated from the 11 240660 piston by a spacer, the spacer having openings provided so that a fluid may flow from one side of the piston to the other.

Alternatively the connecting member may pass through an aperture in one of the pistons, so as to be slidable relative to the piston while providing a 5 seal to prevent fluid flow through the aperture. With this arrangement the piston may be linked to the connecting member by a flange fixed to the connecting member, with a resilient member fitted between the flange and the pistons. Thus the piston may move relative to the connecting member over a predetermined distance until a predetermined force on the piston is 10 attained, at which time the piston may move together with the connecting member.

Since a swept volume of the first and second cylinders may be different due to different bore diameters, a total volume of fluid contained between the first and second pistons may decrease as the first and second pistons move 15 together in one direction. This volume may be discharged from a discharge opening provided in a wall of one of the first or second cylinders, or in the wall of a section of pipe connecting the adjacent ends of the first and second cylinders. Alternatively a part or all of this volume may be accommodated by one or both of the pistons moving relative to the other, 20 such as is possible with the above mentioned arrangement wherein a piston is able to slide on the connecting member under a resilient force.

This increase in volume may also be partially or fully accommodated by a reservoir connected to a discharge passage from the cylinders, such as an accumulator comprising a piston which is slidable in a cylinder under a 25 resilient load.

The first piston may comprise two cup seals mounted back to back on a base plate so as to provide a seal with the bore of the first cylinder in either 12 .. 2406 direction of reciprocal motion. However any sealing means which provides a seal in both directions may be possible. For example an O-ring seal may be possible.

The means for preventing flow in one direction provided at the opposite end of the first cylinder may comprise a ball valve which opens into a reservoir, such as a hopper used for holding the concrete or slurry to be pumped by the pump. The hopper may be removably attached to a mounting frame on which the first and second cylinders are mounted, to facilitate cleaning. Depending on such factors as flow capacity through the ball valve, and other considerations, additional ball valves may be provided, arranged in parallel. However any other type of means for preventing flow in one direction may be possible. For example one or more non-return check valves may be appropriate.

The reciprocating pump may be operated by any suitable mechanism which provides reciprocating motion. In a preferred embodiment this may comprise a hydraulic ram which is connected to the link means directly, such as in the form of an extension of the connecting member. However any suitable connection means may be possible. For example the connection means may comprise an indirect linkage connection using a pivot member.

The hydraulic actuator may comprise a double acting ram wherein a piston may be driven in a hydraulic cylinder in either direction by switching hydraulic fluid flow to either side of the piston. This may be achieved by a standard hydraulic system comprising a diesel engine driving a hydraulic pump wherein the pump pumps hydraulic fluid from a reservoir to a reversing valve. The hydraulic pump may be of a variable 13 240660 displacement type such as a swash plate type so that the operating load and operating speed of the hydraulic actuator may be varied.

However any other form of operating mechanism which provides reciprocating motion is possible. For example a linear motor actuator wherein the drive shaft may be moved in either or both directions as a result of electro-magnetic forces may be possible.

Aspects of the present invention will now be described by way of example only with reference to the accompanying drawings in which: - Figure 1.

Figure 2.

Figure 3.

Figure 4.

Figure 5. is a schematic diagram showing a pump according to a possible embodiment of the present invention, and is a detailed sectional view of the pumping section of the pump of figure 1, and is a detailed sectional view of the hydraulic actuator for the pump of figure 1, and is a sectional view of the accumulator of the pump of figure 1, and is a schematic diagram of a hydraulic control system for the pump of figure 1.

With respect to figure 1, there is provided a reciprocating pump according 20 to an embodiment of the present invention generally indicated by arrow 1. The reciprocating pump 1 comprises a first chamber 2 and a second chamber 3 defined by walls of a cylinder 4 and separated from each other by a piston 5. The first chamber 2 is communicated with the second chamber 3 by way of a ball valve assembly generally indicated by arrow 6 which acts 14 id 4 0 6 6 0 as a means for preventing flow of fluid from the second chamber 3 to the first chamber 2.

The piston 5 may be moved within the cylinder 4 by means of a push rod 7 which is fixedly attached to the piston 5 by way of a cage section 8 which 5 houses a ball 6' of the ball valve assembly 6.

A second cylinder 9 having a second piston 10 slidable therein is arranged substantially coaxial with the first cylinder 4. The first piston 5 and second piston 10 are linked together by the push rod 7 so as to move together with the push rod 7 over their full stroke. The second cylinder 9 is of a smaller 10 bore than the first cylinder 4, and the cylinders 4 and 9 are arranged so that their adjacent open ends communicate with each other, with the push rod 7 passing through the adjacent ends.

With this arrangement, since the first piston 5 and second piston 10 move together with the push rod 7, the displaced volume of the second chamber 3 15 per unit movement of the piston 5 is dependent on the difference in bore diameter between the first cylinder 4 and the second cylinder 9, and is less than the displaced volume of the first chamber 2 per unit movement of the piston 5.

The first cylinder 4 and second cylinder 9 are aligned and sealed by means 20 of a connecting member 11 which has a discharge pipe 12 provided therein for discharge from the second chamber 3. An accumulator generally indicated by arrow 12' is connected to the discharge pipe 12 to minimize surges in the outlet flow.

Another end of the first cylinder 4 is provided with a second ball valve 25 assembly generally indicated by arrow 13 which acts as a second means for preventing flow of fluid from the first chamber 2 out into a hopper 14, while allowing a concrete mixture in the hopper 14 to be drawn into the first chamber 2.

The reciprocating pump 1 is operated by means of a double acting hydraulic actuator generally indicated by arrow 20. A push rod 21 of the hydraulic actuator 20 is formed as continuation of the push rod 7 which is connected to the first and second pistons 5 and 10 respectively. This push rod 21 is operated by differential hydraulic pressure on opposite sides of a piston 22 fitted with seals 22', and which is slidable in a ^cylinder 23 of the double acting hydraulic actuator 20.

The differential pressure across the piston 22 is achieved by means of a reversing valve 24 which directs a flow of hydraulic fluid from a pump 25 to either side of the piston 22. The pump 25 is a variable displacement swash plate type pump which is driven by a diesel engine 26, and draws hydraulic fluid from a hydraulic reservoir 27, provided with an inbuilt cooler 134.

A water box 30 is provided between the second cylinder 9 and the double acting hydraulic actuator 20. The water box 30 provides a means for preventing water leaking from the cylinder 9 from entering into components of the double acting hydraulic actuator 20.

Details of the pumping unit are given in Fig. 2. In this figure components previously described are identified with the same numeral and description is omitted. The second ball valve assembly 13 is connected to a wall portion 21' of the hopper 14 by means of a retaining flange 22' bolted thereto with bolts 23'. An intake tube 24' is bolted to the intake valve housing 26' by means of intake tube retaining bolts 25'. An intake valve ball 27' is housed within the intake valve housing 26' and prevented from moving upwards by ball stops 28. The ball 27' seats on a valve seat 20' so as to prevent flow through the intake tube 24' when seated. An inspection plate 29 is provided 240660 on top of the valve housing 26' for inspection and cleaning of the valve housing. The ball valve assembly is connected to the cylinder 4 by means of ring bolts 31 bolted through a connector ring flange 30. The piston assembly 5 comprises an intake side piston block 32 and an outlet side block 5 33. The blocks 32 and 33 are secured together by 12 retaining bolts. The ball valve assembly 6 comprises a valve seat 34 a cage section 8 and a ball valve 6'. A urethane seal 37 provides a seal between the piston 5 and the walls of the cylinder 4. In operation, grout flow from the hopper 14 through the ball er valve assembly 13 flows in the direction indicated by arrow 40.

Arrow 41 indicates the direction of grout flow out of the second chamber 3. The discharge pipe 12 from the second chamber 3 is fitted with a outlet reducer 44 which is bolted to the outlet of the cylinder 4 by means of a connector ring 42 and bolts 43. The first cylinder 4 and second cylinder 9 are connected together by a transition piece 45 which is bolted to a flange 46 15 on cylinder 4 with flange bolts 47. Tie rods 48 extend between the transition piece 45 and the water box 30 so as to hold the cylinder 9 in position. A concrete seal 49 supported on a seal carrier 50 provides a seal for the end of the cylinder 9. A pin connector 51 connects the second piston 10 to the push rod 21 of the hydraulic actuator 20 by means of a pin 52. A Teflon™ 20 backing plate 53 is clamped to the second piston 10, and the push rod 21 of the hydraulic actuator 20 is threaded onto a pin 54 formed in the connector 51. A triangular rubber seal 59 is also provided between the end of the second cylinder 9 and the transition piece 45 to provide additional sealing and allow for expansion.

Figure 3 shows details of the water box 30 section of the pump 1. The tie rods 48 are bolted to the water box 30 by means of lock nuts 60 which also clamp the water box 30 to the cylinder 9. The water box 30 is fitted with a drain plug 63 which seals against an opening in the bottom thereof. The 17 240660 drain plug 63 is connected to a float 63' so that it may be raised when the level of water 62 in the water box 30 rises above a certain predetermined level as a result of leakage of liquid past the piston 8.

The hydraulic actuator 20 is connected to the opposite side of the water box 5 30 by means of retaining bolts 64. Seal 73 provides a seal between the hydraulic actuator 20 and the water box 30. The piston 22 of the hydraulic ram 20 is provided with O-ring seals 22'. Operation of the hydraulic ram 20 is by means of a pressurized hydraulic supply through a rod side port 69 on the rod side 72 of the piston 22, and a head side port 70 on the head side 71 of 10 the piston 22. A rod side sensing port 67 and a head side sensing port 68 are provided in the walls of the cylinder 23 for providing pressure signals for operation of the hydraulic control system shown in Fig. 5.

Figure 4 shows details of the accumulator 12'. This comprises a standard line coupling 98 whereby the accumulator 12' is connected to the discharge 15 pipe 12. Flow from the discharge pipe 12 is indicated by arrow 100. The accumulator 12' is fitted with a piston stop 81 which provides a limit to movement of a piston assembly comprising a clamp bolt 82, expander plate 83, seal 84, seal carrier 85 and cup seal 86. The piston assembly is sealingly slidable in the bore of an internally chrome plateid cylinder 87. A rubber air 20 bladder 88 is provided above the piston assembly, and is connected by means of a pipe tee 91 to a quick connect air connector 93. The other leg of the tee 91 is connected to a 0-200 psi air pressure gauge 92. An end cap 89 is provided on top of the cylinder 87. The end cap 89 is clamped to the cylinder 87 by means of tie rods and nuts 90, and is sealed with the cylinder 87 by 25 means of an O-ring seal 9^ provided in a groove in the cap 89. Hydraulic oil . 95 is provided on top of the piston assembly to provide lubrication and sealing. The outlet section from the accumulator 12' is co; a-ne'fct'ed '-to a ' /■v ' m>. standard line reducer 97 by means of a line coupling 98. ^ 'i 18 -;-V' V F O ,'V 40660 In operation, flow of grout from the pump 1 is able to flow in and out of the accumulator in the directions indicated by arrow 96. Thus surges in the flow may be accommodated in the accumulator by linear movement of the piston assembly in the cylinder 87. The amount of damping of the surges 5 may be adjusted by adjusting the air pressure in the rubber bladder 88.

Figure 5 shows details of the hydraulic control system. In this figure components described elsewhere are identified with the same numeral and description is omitted for brevity. Flow from the pump 25 passes along an oil supply line 128 through a variable main oil flow control 118 to the main 10 reversing valve 24. With the reversing valve in the position shown in Fig. 5, the hydraulic flow continues along the oil supply line 130 to rod side port 69 so as to operate the rod 21 side of the hydraulic ram 20. Outlet flow from the opposite side of the piston 22 flows through the head side port 70 along the oil line 129, through the reversing valve 24 and passes into the hydraulic 15 reservoir 27 via the oil line 127 and oil line 126. As the piston 22 passes over the sense port 68 provided in the wall of the cylinder 23, a signal pressure is supplied to a right hand side logic valve 110. As a result of this pressure signal, a signal is sent to a pilot valve 112 to operate a piston therein so that a supply pressure from the pump 25 through the pilot oil pressure control 20 117 is supplied to a pilot oil line 132 to operate a piston in the reversing valve 24. As a result supply flow from the oil line 128 is re-diverted to oil line 129 to provide a pressurised flow to head side port 70. Thus the head side of the actuator 20 is pressurised to cause the piston 22 to move in the opposite direction (to the left in the figure).

The hydraulic circuit 5 is further provided with check valve 113 for venting the right hand side of the pilot valve 112, and check valve 114 for venting the left hand side of the pilot valve 112. A double check valve 115 for constant 19 2406-60 pressure sensing for control of the pump 25, is connected via a 0.1mm oil restrictor 133, through a pressure sensor line 125 to a pressure sensor 124 on the pump 25. A relief valve 122 is provided in the pressure sensor line 125 for controlling the maximum pump pressure.

The system is also provided with a main pressure relief valve 123 and on/off valve for on/off control of the hydraulic system. This discharges through the return oil line 126. A reversing valve 79 is also provided whereby the connection to ports 67 and 68 may be reversed. This results in the reversal of the piston 22 movement. This feature may be used for releasing blockages in the cylinders. Furthermore, manual shut off valves 77 and 78 are provided on the signal lines from the head side port 68 and from the rod side port 67 respectively. These manual shut off valves are for isolating the pilot valve 112, so that the actuator 20 may be controlled manually for certain operations. For example, manual control may be used during cleaning and maintenance after the second ball valve assembly 13 has been removed, to move the piston 22 well past the rod side port 67 thereby extending the piston 5 and ball valve assembly 6 out the end of the cylinder 4.

In operation of the reciprocating pump 1, the first and second pistons 5 and 10 respectively are driven away from the chamber 2 (to the right in the figure) by means of a higher pressure on the push rod 21 side of the piston 22 of the double acting hydraulic actuator 20. As the first and second pistons 5 and 10 respectively move in the first and second cylinders 4 and 9 respectively, the volume defined between the first and second pistons 5, and 10 respectively decreases due to the difference in bore diameter of the first . and second cylinders 4 and 9 respectively. At the same time the ball of the ball valve 6 seals against a seat in the aperture in the first piston 5. Consequently some of the concrete mixture contained between the first ) c. 40660 piston 5 and the second piston 10 is discharged through the discharge nozzle 12. At the same time concrete mixture is drawn into the first chamber 2 through the ball valve 13 from the hopper 14.

When the first and second pistons 5 and 10 respectively reach the end of 5 their stroke, the hydraulic supply to the double acting hydraulic actuator 20 is reversed by means of the valve 24 so that the piston 22 is driven in an opposite direction (to the left in the figure). During this reverse stroke, the ball of the ball valve 13 seals against its seat and the ball of the ball valve 6 separates from its seat in the piston 5 so that concrete mixture contained in 10 the chamber 2 can pass through the aperture in the piston 5 into the chamber 3. Since the second piston 10 is moving to the left, the sum of the volumes of the first chamber 2 and the second chamber 3 is decreasing so that concrete mixture is again discharged from the discharge nozzle 12.

During this reverse stroke, for a constant flow rate from the pump 25, the 15 stroke speed will be reduced since the displaced volume on the higher pressure side of the piston 22 is less as there is no push rod 21 on this side to take up extra volume.

With such an arrangement, the discharge volume of concrete due to movement of the first and second pistons 5 and 10 in one direction may 20 differ from the discharge volume due to movement of the first and second pistons 5 and 10 in the other direction. This difference in discharge volume may be adjusted by suitable selection of bore diameters of the first cylinder 4 and the second cylinder 9. In order to obtain a smooth outlet flow, the speed of the first and second pistons 5 and 10 in one direction may be made 25 different from the speed in the opposite direction. This may be best achieved by suitable selection of the diameter of the push rod 21 which affects the displaced volume per unit movement of the piston 22, and hence 21 240660 the speed of movement for a constant flow rate of hydraulic fluid from the pump 25.

I believe the advantages of my invention to be as follows however it should be appreciated that all such advantages may not be realised on all 5 embodiments of the invention, and the following list is given by way of example only as being indicative of potential advantages of the present invention. Furthermore, it is not intended that the advantages of the present invention be restricted to those of the list which follows: - 1. By arranging these cylinders of the reciprocating pump substantially co axial to each other, the size of the pump may be reduced. Furthermore, a common push rod may be used, thereby simplifying the mechanism and the number of moving components. 2. The arrangement of components enables a simple design aimed at 15 providing a continuous flow, since optimum flow discharge may be designed for by choosing suitable bore diameters of the first and second cylinders in conjunction with suitable selection of the hydraulic actuator bore diameter and/ or push rod diameter to obtain optimum operating speed in each direction. 3. Pulses in the flow may be smoothed out by having the second piston slidable on the push rod over a predetermined distance under the loading of a resilient member. Alternatively a separate pulse damping reservoir may be easily connected to the second chamber. 4. A low vibration system is possible since a hydraulic actuator with 25 remote hydraulic supply is possible. 22 4 0 6 6 0 C- . The enclosed nature of the design protects the components from damage and contamination in a harsh operating environment. 6. Blockage of outlet/inlet pipes may be easily sensed as an increase in the load on the push rod. With an hydraulic actuator type drive, this increase in load may best be sensed by a pressure gauge in the hydraulic supply line. On sensing an overload, the operation of the pump may be easily stopped by means of a relief valve or the like. Reversing of the pump to reduce pressure may also be possible by reversing the supply pressure to the hydraulic actuator. 7. With an embodiment of the present invention, it may be possible to arrange the non-return valves so that a suction may be achieved in the discharge nozzle 12 so as to draw concrete back up the discharge pipe. This may be achieved by a design wherein an intake valve to the first chamber 2 may be shut off and a valve 15 positioned in a pipe connecting the first chamber 2 to the second chamber 3 may be opened to allow concrete in the second chamber 3 to flow back into the first chamber 2 as the piston 10 is moved away from the first chamber 2.

Aspects of the present invention have been described by way of example 20 only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims. 23

Claims (4)

240 660 WHAT I CLAIM IS;

1. A reciprocating fluid pump comprising a first housing, a first chamber and a second chamber within the housing separated by a valve in a first piston which allows fluid to flow from the first chamber to the second chamber, a piston rod connected to the first piston and to second and third pistons housed within a second housing which extends from the first housing, hydraulic actuator means to effect reciprocation of the second and third pistons within the second housing and the first piston within the first housing, one way ball valves within the first piston and at an entrance of the first chamber, and an outlet from the second chamber, said first housing being of a greater diameter than the second housing, the arrangement being such that on reciprocation of the pistons fluid is drawn through the entrance into the first chamber on an inward stroke and discharged via said second chamber on the reverse stroke. ' ' ' '' * '

2. A reciprocating fluid pumps as claimed in claim 1 wherein the entry is at right angles to the piston chambers enabling fluid to be gravity fed into the pump whilst the pump is in a horizontal disposition.

3. A reciprocating fluid pump as claimed in claim 2 wherein the valves are ball valves and the balls are freely floating.

4. A reciprocating pump as claimed in any one of claims 1 to 3 wherein the valve in the first piston valve comprises a cage body for housing a floating ball said cage body having front and^rear sections, the rear section of the cage body being comilcted to g ? ' & -1 ■ 1S95 *Jj 24 / 240660 piston rod for the pump and the front section of the cage body mounting back-to-back cup seals the outer periphery of each up \ seal extending beyond surfaces of the piston to walls of the chamber in which the piston reciprocates. A reciprocating fluid pump substantially as herein described with -reference to the accompanying drawings. IAN DOUGLAS DE MEY By His Attorneys ' * " '' ' . . w • JAMES & WELLS ' "vL'Jr ■:;-V '•'v W.V. .. . v - - "^V 1-■ ■ -U. ■ 25