US3556692A

US3556692A - High pressure liquid pump

Info

Publication number: US3556692A
Application number: US804102A
Authority: US
Inventors: Albert Edward Pigott; Peter John Thompson
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1968-03-08
Filing date: 1969-03-04
Publication date: 1971-01-19
Anticipated expiration: 1988-01-19
Also published as: DE1911541A1; FR2003489A1; SE344490B; CH496890A; GB1257781A; JPS503002B1

Abstract

A HIGH PRESSURE PUMP HAS A PUMP CYLINDER CONTAINED BY AN OUTER PRESSURE VESSEL, AN INTERSPACE BEING DEFINED BETWEEN THE PUMP CYLINDER AND THE PRESSURE VESSEL. LIQUID IS PRESSURISED IN THE PUMP CYLINDER BY A PISTON AND PRESSURISED LIQUID IS FED THROUGH A NONRETURN VALVE FROM THE PUMP CYLINDER INTO THE INTERSPACE ON THE PRESSURISING STROKE OF THE PISTON. SUPPLY OF LIQUID BY THE PUMP AT

CONSTANT PRESSURE IS FROM THE INTERSPACE. AN ACCUMULATOR SPACE OF VARIABLE VOLUME MAY BE PROVIDED CONNECTED WITH THE INTERSPACE TO ACCOMMODATE FOR DIFFERENCES BETWEEN THE RATE OF SUPPLY OF LIQUID FROM THE INTERSPACE AND THE RATE OF FEED OF LIQUID FROM THE PUMP CYLINDER INTO THE INTERSPACE.

Description

Jan. 19, 1971 PiGOTT ETAL 3,556,692

I HIGH PRESSURE LIQUID PUMP Filed March 4, 1969 2 Sheets-Sheet 1 Jan. 19, 1971 A. E. PIGOTT ETAL HIGH PRESSURE LIQUID PUMP 2 Sheets-Sheet 2 Filed March 4, 1969 United States Patent 3,556,692 HIGH PRESSURE LIQUID PUMP Albert Edward Pigott, Clifton, Preston, and Peter John Thompson, St. Annes-on-Sea, England, assignors to United Kingdom Atomic Energy Authority, London, England Filed Mar. 4, 1969, Ser. No. 804,102 Claims priority, application Great Britain, Mar. 8, 1968, 11,590/68 Int. Cl. F04b 11/00 US. Cl. 417-540 8 Claims ABSTRACT OF THE DISCLOSURE A high pressure pump has a pump cylinder contained by an outer pressure vessel, an interspace being defined between the pump cylinder and the pressure vessel. Liquid is pressurised in the pump cylinder by a piston and pressurised liquid is fed through a nonreturn valve from the pump cylinder into the interspace on the pressurising stroke of the piston. Supply of liquid by the pump at constant pressure is from the interspace. An accumulator space of variable volume may be provided connected with the interspace to accommodate for differences between the rate of supply of liquid from the interspace and the rate of feed of liquid from the pump cylinder into the interspace.

BACKGROUND OF THE INVENTION This invention relates to high pressure fluid pumps and in particular to an improved high pressure fluid pump capable of delivering a continuous flow of high pressure fluid at a high flow rate and at a steady feed pressure.

There is an application for such a pump, particularly for the pumping of liquids, in many fields of high pressure technology, particular applications being in respect of the isostatic compaction of powders and the hydrostatic extru! ion process.

In the hydrostatic extrusion process a billet is extruded from a chamber through a die by pressurisation of liquid in the chamber about the billet. Liquid may be pressurised about the billet by a ram acting in the bore of the extrusion chamber itself, the billet being extruded by a single stroke of the ram. Unfortunately in this way of carrying out the process, instability of the ram by buckling leads to restriction of the ram length to diameter ratio which may be used. Hence because of the limitation imposed on ram length to diameter ratio a limitation is imposed on the length of extrusion chamber which can be employed. To overcome this ditficulty and enable the use of an extrusion chamber of large length to diameter ratio it has been proposed to generate liquid pressure in a separate pump, having a pump cylinder of equal volume to the volume of liquid required for carrying out extrusion of the billet, but having a length to diameter ratio small enough to avoid bucking of the pump piston. In order to achieve this, the diameter of the pump cylinder is always much larger than that of extrusion container, thus increasing the cost of the equipment. This difliculty is overcome if the required volume of high pressure liquid for the extrusion process is delivered to the extrusion container by a pump having a small cylinder in which the pump piston undergoes several strokes.

A difiiculty arises in use of a pump as described above due to the limited fatigue life of the pump cylinder which is subjected to alternating high and low internal pressures and hence to a cyclic tensile strain variation. Also supply of liquid by the pump is intermittent as feed occurs only on the pumping stroke of the piston.

Pressure cycling in the bore of the extrusion chamber may be avoided by provision of a hydraulic accumula- 3,556,692. Patented Jan. 19, 1971 tor in the feed line from the pump to the extrusion chamber, but the fatigue life of the pump cylinder remains the limiting factor.

SUMMARY OF THE INVENTION According to the invention a high pressure fluid pump has its cylinder contained by a pressure vessel, an interspace being defined between the pump cylinder and the pressure vessel, means being provided for controlled feeding of pressurised fluid from the pump cylinder into the interspace, supply of pressurized fluid at constant pressure being from the interspace.

The interspace defined between the pump cylinder and the pressure vessel may be of variable volume to accommodate for differences between the rate of feeding of fluid from the pump cylinder into the interspace and the rate of supply of pressurised fluid from the interspace.

In another arrangement a separate fluid accumulator space of variable volume is provided connected with the interspace defined between the pump cylinder and the pressure vessel to accommodate for diiferences between the rate of feeding of fluid from the pump cylinder into the interspace and the rate of supply of pressurised fluid from the interspace. In this case the fluid accumulator space may be an extension of the interspace defined between the pump cylinder and the pressure vessel, variation of the volume of the fluid accumulator space being obtained by longitudinal movement of the pump cylinder and the pressure vessel relative to each other. In a particular arrangement the pump cylinder may have an axial extension of smaller cross section than the main body of the pump cylinder, the axial extension of the pump cylinder being sealed in passage through the wall of the pressure vessel and the fluid accumulator space of variable volume being defined between the axial extension of the pump cylinder and the pressure vessel, variation of the volume of the fluid accumulator space being obtained by longitudinal movement of the pump cylinder and the pressure vessel relative to each other.

The means for controlled feeding of pressurised fluid from the pump cylinder into the interspace between the pump cylinder and the pressure vessel may be a nonreturn valve. In a particular arrangement the means for controlled feeding of pressurised fluid from the pump cylinder into the interspace between the pump cylinder and the pressure vessel may comprise a valve seating around one end of the bore of the pump cylinder, the valve seating bearing against a valve member at the end of the pump cylinder, means being provided for establishing a pressure between the valve seating and the valve member to control the pressure at which fluid feeds between the valve seating and the valve member from the pump cylinder into the interspace. In this arrangement the pump cylinder may have the feature of an axial extension of smaller cross section than the main body of the pump cylinder, the axial extension of the pump cylinder being sealed in passage through the wall of the pressure vessel, a fluid accumulator space being thus defined between the axial extension of the pump cylinder andthe pressure vessel, the pressure vessel being longitudinally movable relative to the pump cylinder whereby the fluid accumulator space is of variable volume to accommodate for differences between the rate of feeding of fluid from the pump cylinder into the interspace and the rate of supply of pressurised fluid from the interspace, means being provided for loading the pressure vessel longitudinally to maintain the pressure of the fluid in the accumulator space and in the interspace between the pump cylinder and the pressure vessel, the pressure of the fluid in the accumulator space acting on a shoulder between the axial extension of the pump cylinder and the main body of the pump cylinder to apply a longitudinal loading on the pump cylinder, which establishes the pressure between the valve seating and the valve member to control the pressure at which fluid feeds from the pump cylinder into the interspace.

A plunger or piston may be provided in the bore of the pump cylinder for induction of fluid into and pressurisation of fluid in the pump cylinder, the means for loading the pressure vessel longitudinally to maintain the pressure of fluid in the accumulator space and in the interspace between the pump cylinder and the pressure vessel comprising a low pressure piston and cylinder arrangement acting on the pressure vessel, the cylinder of the piston and cylinder arrangement having a connection with the bore of the pump cylinder through a nonreturn valve for feed of low pressure fluid into the pump cylinder on the induction stroke of the plunger in the pump cylinder.

The invention is particularly concerned with a high pressure pump in which fluid pressure in the pump cylinder varies cyclically during pumping. This is the case for example where pumping is performed by a reciprocating ram or piston operating in the pump cylinder. Normally the pump cylinder would be subjected to a cyclic tensile strain variation. However as the high pressure liquid in the interspace between the pump cylinder and the pressure vessel acts on the outer surface of the pump cylinder the pump cylinder will only be subjected to compressive cyclic strains. The fatigue life of the pump cylinder under this type of loading will be greater than in the case where the outer surface of the pump cylinder is unsupported and the pump cylinder is subjected to a tensile cyclic strain variation. As the pressure of the liquid in the interspace between the pump cylinder and the pressure vessel is constant therefore the pressure vessel will not be fatigued.

DESCRIPTION OF THE DRAWINGS An embodiment of the invention will now be described with reference to the accompanying drawings in which: FIG. 1 is a centre line section of a high pressure liquid pump according to the invention.

FIG. 2 is a schematic arrangement of a typical application of the pump in hydrostatic extrusion apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the construction shown in FIG. 1 of the drawings a high pressure hydraulic pump comprises a bed plate 1 on which there is mounted a pump base 2. The pump base 2 comprises a circular plinth 3 having an integral flange 4 and is mounted on the bed plate 1 by bolts 5.

A low pressure cylinder 6 is a sliding fit on the flange 4 of the pump base 2, the low pressure cylinder 6 having an annular base 7, which is a sliding fit about the plinth 3 of the pump base 2. Sealing between the cylinder 6 and the flange 4 of the pump base 2 is by means of a low pressure seal 8 whilst sealing between the end wall of the cylinder 6 and the plinth 3 of the pump base 2 is by means of a low pressure seal 9.

A pump cylinder 10 is mounted on the pump base 2. The pump cylinder 10 has a longitudinal bore 11 with a counterbore 12 at its lower end which fits about an upstanding valve member 13 on the pump base 2. The counterbore 12 has a flat seating 14, which seats on the upper end face of the valve member 13. The flat seating 14 of the counterbore 12 and the upper end face 15 of the valve member 13 have

hard metal facings

16 and 17 respectively. The upper end of the valve member 13 is of reduced diameter so defining an annular space 18 in the counterbore 12 of the pump cylinder 10. The valve member 13 is sealed in the counterbore 12 by a mitre ring and O-ring seal 19. An outer pressure vessel 20 is fitted about the pump cylinder 10 and is clamped end to end with the low pressure cylinder 6 by bolts 21. The cojoined cylinder 6 and the outer pressure vessel 20 slide vertically on guide pillars 22 which are screwed into the bed plate 1, the upper ends of the pillars 22 being screwed into a fixed support ring 23. The low pressure cylinder 6 is fitted in a support flange 24 having guide bushes 25 which are a sliding fit on the guide pillars 22. The outer pressure vessel 20 is fitted with a support flange 26 having guide bushes 27 which are also a sliding fit on the guide pillars 22.

An annular interspace 28 is defined between the bore 29 of the outer pressure vessel 20 and the pump cylinder 10. A mitre ring O-ring seal 30 seals between the lower end of the bore 29 of the outer pressure vessel 20 and the outer surface of the pump cylinder 10.

The pump cylinder 10 has an upper extension 31 of smalled external diameter than the main body of the pump cylinder 10. An annular plug 32 is screwed into the upper end of the bore 29 in the outer pressure vessel 20. A sealing ring 33 seals between the bore 29 of the outer pressure vessel 20 and the extension 31 of the pump cylinder 10 below the plug 32. A pressurised oil accumulator space 34 is defined in the upper end of the bore 29 of the vessel 20 surrounding the upper extension 31 of the pump cylinder 10.

A liquid pressurising ram 35 is entered into the bore 11 of the pump cylinder 10. The ram 35 is sealed in the bore 11 of the pump cylinder 10 by a mitre ring and O- ring seal 36.

An oil inlet port 37 for inlet of a feed of low pressure oil into the pump is provided in the plinth 3 of the pump base 2. The inlet port 37 is connected with the low pressure cylinder 6 by a cross drilling 38 in the pump base 2. A second cross drilling 39 in the pump base 2 connects with a low pressure oil inlet port 40 in the valve member 13 of the pump base 2. The inlet of oil from the port 40 into the bore 11 of the pump cylinder 10 is controlled by means of a high pressure nonreturn valve 41 fitted in the valve member 13. A low pressure oil feed line 42 is connected with the oil inlet port 37 by a threaded union nut 43. A high pressure oil delivery port 44 in the valve member 13 of the pump base 2 leads from the annular space 18 defined in the counterbore 12 of the pump cylinder surrounding the upper end of the valve member 13. A cross drilling 45 in the pump cylinder 10 connects the annular space 18 with the annular interspace 28 defined between the bore 29 of the outer pressure vessel 20 and the pump cylinder 10. A high pressure oil out let line 46 is connected with the high pressure oil delivery port 44 by a threaded union nut 47.

In operation of the pump described above low pressure oil is supplied from the oil feed line 42 to the oil inlet port 37 and the low pressure cylinder 6 (via the cross drilling 38). During the upward induction stroke of the ram 35 in the bore 11 of the pump cylinder 10, low pressure oil enters the bore 11 from the low pressure cylinder 6 via the cross drilling 39 and the oil inlet port 40 through the open high pressure nonreturn valve 41. The downward pressurising stroke of the ram 35 closes the high pressure nonreturn valve 41 and increases the oil pressure in the bore 11 of the pump cylinder 10 until a pressure is achieved which forces oil to pass under pressure from the bore 11 of the pump cylinder 10 between the end face 15 of the valve member 13 and the flat seating 14 of the counterbore 12 in the pump cylinder 10. The pressurised oil enters the annular space 18 in the counterbore 12 and from the annular space 18 the pressurised oil passes through the cross drilling 45 into the interspace 28 defined between the outer pressure vessel 20 and the pump cylinder 10.

Supply of oil by the pump at constant pressure is from the annular space 18 the oil passing through the delivery port 44 to the outlet line 46.

If the feed rate of pressurised oil from the pump cylinder 10 into the annular space 18 and the interspace 28 is in excess of supply requirements during the pressurising stroke of the ram 35 the excess oil passes into the accumulator space 34. In order to accommodate this flow of high pressure oil into the accumulator space 34 the outer high pressure vessel 20 together with the low pressure cylinder 6 moves vertically upwards, guided by the pillars 22. The pressure of oil in the low pressure cylinder 6 provides a reaction to the load exerted by the high pressure oil in the accumulator space 34 on the annular plug 32. The upward movement of the pressure vessel 20 and the cylinder 6 increases the volume of the accumulator space 34 to accommodate the excess oil and maintains a constant oil delivery pressure in the delivery port 44 during the compression stroke of the ram 35. During the induction stroke of the ram 35 the oil delivery pressure in the delivery port 44 is maintained constant by the downward movement of the cojoined pressure vessel 20 and cylinder 6, forcing high pressure oil to flow out of the accumulator space 34 down the annular space 28 into the delivery port 44. Thus a feed of high pressure oil is supplied by the pump at a constant required rate both during the induction and pressurising strokes of the ram 35.

The pressure of the oil in the accumulator space 34 acting on the external shoulder 48 of the pump cylinder 10 applies a downwards loading on the pump cylinder 10 so that the flat seating 14 in the counterbore 12 of the pump cylinder 10 is pressed against the upper end face of the valve member 13 on the pump base 2.

The contact pressure exerted between the seating 14 of the counterbore 12 and the upper end face 15 of the valve member 13 controls the pressure at which oil bleeds from the bore 11 of the pump cylinder 10. This contact pressure is dependent on the area of the external shoulder 48 of the pump cylinder 10 relative to the area of the base 14 in the counterbore 12 of the pump cylinder 10.

FIG. 2 shows one use of the pump in supplying high pressure oil to hydrostatic extrusion equipment which comprises a long bore extrusion chamber 49 fitted with an extrusion die 50. A billet 51 of large length to diameter ratio is extruded through the die 50 by pressurisation of oil surrounding the billet 51 in the bore of the chamber 49. High pressure oil is supplied to the bore of the chamber 49 from a pump 52 of the kind described above, the high pressure oil outlet line 46 of the pump being connected with an oil inlet port 53 at the rear end of the extrusion chamber 49. Low pressure oil is supplied to the pump through the low pressure oil feed line 54 from a low pressure oil supply system 55.

Connected into the low pressure oil feed line 54 is a low pressure oil accumulator 56, which allows a fiow of low pressure oil into and out of the oil inlet port 37 and the low pressure cylinder 6 of the pump in accordance with the vertical movement of the outer pressure vessel and the low pressure cylinder 6 of the pump thus maintaining a constant pressure supply of low pressure oil in the oil inlet port 37. The low pressure oil supply system 55 comprises an oil tank, a low pressure pump driven by an electric motor together with means for cooling and filtering the oil. Oil leakage from the die 50 of the extrusion chamber 49 is returned to the low pressure oil supply system 55 from an oil leakage tank 57 by means of a pump 58 and an oil return pipe 59.

In the construction shown in FIG. 1 of the drawings the pump cylinder 10 is acted On by oil pressure on both its inner and outer surfaces. The outer surface of the pump cylinder 10 is supported by the high pressureoil in the annular interspace 28. The inner surface, however, is subjected to the oil pressures acting in the bore 11 and undergoes a cyclic variation from the low pressure of the oil entering the bore 11 from the oil inlet port 37 to the high pressure required to cause the oil to bleed from the bore 11 of the pump cylinder 10, this pressure exceeding the delivery pressure by a small amount.

With this type of pressure loading the pump cylinder 10 is subjected to compressive cyclic strains. Whilst it is known that this type of strain variation does induce fatigue failure, experiment has shown that the fatigue life is greater than when the pump cylinder is subjected to a tensile cyclic strain variation. The outer pressure vessel 20 however, is not fatigued as the pressure in the annular interspace 28 is constant. However in applications where the supply pressure varies according to the requirements of the process being supplied, the outer pressure vessel 20 is still only fatigued by one strain cycle in each performance of the process.

We claim:

1. A high pressure fluid pump having a cylinder contained by a pressure vessel, a reciprocable plunger for pressurising fluid in the cylinder, an interspace being defined between the cylinder and the pressure vessel, means being provided for controlled feeding of pressurized fluid from the pump cylinder into the interspace, means for supplying at a constant rate pressurized fluid at constant pressure from the interspace, the interspace defined between the pump cylinder and the pressure vessel being of variable volume to accomodate for differences between the rate of feeding of fluid from the pump cylinder into the interspace and the rate of supply of pressurized fluid from the interspace to thereby provide said constant rate supply.

2. A high pressure fluid pump as claimed in claim 1 wherein a separate fluid accumulator space of variable volume is provided in connection with the interspace defined between the pump cylinder and the pressure vessel to accommodate for differences between the rate of feeding of fluid from the pump cylinder into the interspace and the rate of supply of pressurised fluid from the interspace.

3. A high pressure fluid pump as claimed in claim 2 wherein the fluid accumulator space is an extension of the interspace defined between the pump cylinder and the pressure vessel, variation of the volume of the fluid accumulator space being obtained by longitudinal movement of the pump cylinder and the pressure vessel relative to each other.

4. A high pressure fluid pump as claimed in claim 2 wherein the pump cylinder has an axial extension of smaller cross section than the main body of the pump cylinder the axial extension of the pump cylinder being sealed in passage through the wall of the pressure vessel and the fluid accumulator space of variable volume being defined between the axial extension of the pump cylinder and the pressure vessel, variation of the volume of the fluid accumulator space being obtained by longitudinal movement of the pump cylinder and the pressure vessel relative to each other.

5. A high pressure fluid pump as claimed in claim 1 wherein the means for controlled feeding of pressurised fluid from the pump cylinder into the interspace between the pump cylinder and the pressure vessel is a nonreturn valve.

6. A high pressure fluid pump as claimed in claim 1 wherein the means for controlled feeding of pressurised fluid from the pump cylinder into the interspace between the pump cylinder and the pressure vessel comprises a valve seating around one end of the bore of the pump cylinder, the valve seating bearing against a valve member at the end of the pump cylinder, means being provided for establishing a pressure between the valve seating and the valve member to control the pressure at which fluid feeds between the valve seating and the valve member from the pump cylinder into the interspace.

' 7. A high pressure fluid pump as claimed in claim 6 wherein the pump cylinder has an axial extension of smaller cross section than the main body of the pump cylinder the axial extension of the pump cylinder being sealed in passage through the wall of the pressure vessel, a fluid accumulator space being thus defined between the axial extension of the pump cylinder and the pressure vessel, the pressure vessel being longitudinally movable relative to the pump cylinder whereby the fluid accumulator space is of variable volume to accommodate for differences between the rate of feeding of fluid from the pump cylinder into the interspace and the rate of supply of pressurised fluid from the interspace, means being provided for loading the pressure vessel longitudinally to maintain the pressure of the fluid in the accumulator space and in the interspace between the pump cylinder and the pressure vessel, the pressure of the fluid in the accumulator space acting on a shoulder between the axial extension of the pump cylinder and the main body of the pump cylinder to apply a longitudinal loading on the pump cylinder which establishes the pressure between the valve seating and the valve member to control the pressure at which fluid feeds from the pump cylinder into the interspace.

8. A high pressure fluid pump as claimed in claim 7 wherein a plunger is provided in the bore of the pump cylinder for induction of fluid into and pressurisation of fluid in the pump cylinder, the means for loading the pressure vessel longitudinally to maintain the pressure of fluid in the accumulator space and in the interspace between the pump cylinder and the pressure vessel comprising a low pressure piston and cylinder arrangement acting on the pressure vessel, the cylinder of the piston and cylinder arrangement having a connection with the bore of the pump cylinder through a nonreturn valve for feed of low pressure fluid into the pump cylinder on the induction stroke of the plunger in the pump cylinder.

References Cited UNITED STATES PATENTS 2,891,564 6/1959 Jeromson, Jr. 103-223X 3,005,412 10/1961 Camp 103223X 3,027,848 4/1962 Merkle 103223X 3,128,941 4/1964 Waibel 103-153X ROBERT M. WALKER, Primary Examiner