NZ264276A - Valve and piston assembly for reciprocating pump: valve has cage with floating ball and piston has back to back cup seals - Google Patents

Description

264276 PATENTS FORM NO. 5 Fee No. 4: $260.00 PATENTS ACT 1953 COMPLETE SPECIFICATION 1 After Provisional ff I " No: 264276 Dated; 19 August 1994 IMPROVEMENTS IN OR RELATING TO CONCRETE PUMPS I Ian Douglas De Mey, a New Zealand citizen of 47 Ireland Road, Panmure, Auckland, New Zealand hereby declare the invention for which I/We pray that a patent may be granted to me/us, and the method by which it is to be performed to be particularly described in and by the following statement: 1 264276 IMPROVEMENTS IN OR RELATING TO PUMPS Technical, field This invention relates to pumps.

Background Art The invention may be particularly suitable as a reciprocating pump for pumping dual phase fluids such as slurries and concrete, and the present invention is directed to such applications. My co-pending New Zealand Patent Application No. 240660 describes such a pump and the disclosure thereof is referred to by way of background to the present invention.

I have found that for the efficient operation of pumps of the type described in New Zealand Patent Application No. 240660, the construction and geometry of the main piston valve is critical It is an object of the present invention to provide an improved piston for a reciprocating pump of the kind described.

Further objects and advantages of the present invention will become apparent from the ensuing description which is given by way of example. disclosure of invention According to the present invention there is provided a valve and a piston for a pump chamber of a pump of the type described, said valve comprising a cage body for housing a floating ball, the cage body having front and rear sections, the rear section of the cage body being connected to a piston rod for the pump and the front section of the cage body mounting a piston having back-to-back cup seals the outer periphery of each cup seal extending 264276 beyond surfaces of the piston to walls of the chamber in which the piston reciprocates.

The outer periphery of each cup seal is tapered.

The distance S (as defined herein) between the outer edges of the cage and the piston chamber is greater than the aggregate size for which the pump is specified.

The distance X (as defined herein) between the outer periphery of the ball within the valve cage when centralised and the cage wall is greater than the aggregate size for which the pump is specified.

The cup seals of the assembly are compressed.

The piston is connected to an end portion of the cage body by a pair of locating rings.

The locating rings each have chamfered outer peripheral edges.

Aspects of the present invention will now be described with reference to the accompanying drawings in which; Figure 1: is a schematic diagram showing a pump according to a possible embodiment of the present invention, and Figure 2: is an enlarged cross-sectional view of the first chamber and piston within it.

With respect to figure 1, there is provided a reciprocating pump according 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 264276 3 by way of a ball valve assembly generally indicated by arrow 6 which acts 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 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 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 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 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 minimise surges in the outlet flow.

Another end of the first cylinder 4 is provided with a second ball valve assembly generally indicated by arrow 13 which acts as a second means for 264276 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.

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 wat.er leaking from the cylinder 9 from entering into components of the double acting hydraulic actuator 20.

Figure 2 of the drawings is an enlarged view of the first piston 5 within cylinder 4 and shows cage 8 and its assembly to piston 5.

The piston 5 is mounted to cage 8 and embodies cup seals illustrated. The end 32 of the cage 8 to which the piston is mounted is provided with an outer stepped end face 33 and an inner stepped inner face 34. Face 33 accepts a complimentary end 35 of piston sleeve 351 and locates the inner flange 36 of a first cupped seal generally indicated by arrow 37.

A central portion 38 of sleeve 351 mounts a wearing sleeve 39.

A wedge shaped locking ring 40 serves to seal off the inner side of a compression cavity 41 between block end 35 and an adjacent surface of ring 40.

The block end 43 is dimensioned to provide a cavity 44 for a second oppositely orientated cup seal 37 and also provides an inner shoulder 46 to facilitate the securement and compression of a second cup seal 37 in the position shewn.

A curved surface 48 of a cap 47 minimises flow disruption and chamfered shoulders 49, 50 define one side of a cavity 51 beneath the limbs 52 of each of the seals.

The piston 5 is assembled using bolts 53 which join sleeve 351, caps 47 and 32 of the cage 8 and facilitate gripping of the flanges 36 of the cap seals 37. During trials of the apparatus I have found that it is critically important to provide design tolerances which have regard to the type of aggregate the pump is specified for. Where for example the pump is specified for pumping concrete having 10mm aggregates distance S between the outer edges of the cage 8 and the cylinder 4 should be 12-14mm and a similar "oversize" gap "X" should exist between the outer extremities of a ball within the cage 8 and the inner walls of the cage, whilst the opening SI which provides valve seat 55 should be as wide as possible.

The cage 8 may be characterised by four limbs 56) the chambered edges 49, 50 beneath the limbs 52 of each of the cap seals play an important role in preventing abrasion damage and potential blockages.

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 embodiments of the invention, and the following list is given by way of example only as being indicative of potential advantages of the present / b " 264276 iQ 264276 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 providing a continuous flow, since optimum flow discharge may be designed for by choosing statable 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 remote hydraulic supply is possible.

. 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. 7 264276 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 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 . only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined by the appended claims.

Claims (6)

what i claim is: 26 A 276

1. A valve and a piston for a pump chamber of a pump of the type hereinbefore described, said valve comprising a cage body for housing a floating ball, the cage body having front and rear sections, the rear section of the cage body being connected to a piston rod for the pump and the front section of the cage body mounting a piston having back-to-back cup seals the outer periphery of each cup seal extending beyond surfaces of the piston to walls of the chamber in which the piston reciprocates.

2. A valve and a piston as claimed in claim 1 wherein the outer periphery of each cup seal is tapered.

3. A valve and a piston as claimed in anyone of claim 1 or claim 2 wherein the distance S (as defined herein) between the outer edges of the cage and the piston chamber is greater than an aggregate size for which the pump is specified.

4. A valve and a piston as claimed in any one of claims 1 to 3 wherein the distance X (as defined herein) between the outer periphery of the ball within the valve cage when centralised and the cage wall is greater than the aggregate size for which the pump is specified.

5. A valve and a piston as claimed in anyone of claims 1 to 4 wherein the cup seals of the assembly are compressed.

6. A valve and a piston as claimed in any one of claims 1 to 5 wherein the piston is connected to an end portion of the cage body by a pair of locating rings. __ ~~j 30 SEP 139/ I 264276 A valve and a piston as claimed in claim 6 wherein the locating rings each have chamfered outer peripheral edges. A valve and a piston substantially as herein described with reference to the accompanying drawings. to Douglas Pq May By His Attorneys END OF CLAIMS