GB2068476A

GB2068476A - Radial-piston pump

Info

Publication number: GB2068476A
Application number: GB8101955A
Authority: GB
Original assignee: Gewerkschaft Eisenhutte Westfalia GmbH
Current assignee: Gewerkschaft Eisenhutte Westfalia GmbH
Priority date: 1980-02-01
Filing date: 1981-01-22
Publication date: 1981-08-12
Also published as: FR2475151B1; GB2068476B; DE3003590A1; PL228815A1; DE3003590C2; FR2475151A1; JPS56129774A

Abstract

A radial-piston pump for delivering a water-oil emulsion at high pressure, especially a water-oil emulsion whose oil content is less than 12%, has a housing 10, a shaft 11 rotatably mounted in the housing, and a plurality of sets of radial piston-and-cylinder units 14, 15. The units 14, 15 of the or each set are symmetrically disposed about the shaft 11. Each of the pistons 15 is reciprocably driven within its cylinder 14 by means of an eccentric cam 13 fixed to the shaft 11. Each of the piston-and-cylinder units 14, 15 is provided with an inlet valve 21 for controlling the flow of emulsion from the interior 17 of the housing 10 to that unit. Each of the pistons 15 has a maximum diameter of 12 millimetres, and the length of that part of each piston which is guided in its cylinder 14 is at least two and a half times the diameter of that piston. Each inlet valve 21 has a flow cross-section of greater area than the cross-sectional area of the piston 14 of that unit. <IMAGE>

Description

SPECIFICATION Radial-piston pump This invention relates to a radial-piston pump for delivering a high-pressure water-oil emulsion, particularly for pressurising the hydraulic advance rams associated with the elongate planks (knives) of a knife shield used in tunnelling.

Tunnel drive shields (such as knife shields) are used to form the roadways or galleries of undergound mines, as well as for forming tunnels, trenches and the like. The planks (knives) of such knife shields are advanced by hydraulic rams, which must be supplied with hydraulic fluid at pressures of between 300 and 500 bars. For this purpose, use has hitherto been made of slowrunning axial-piston pumps which deliver the hydraulic fluid at the required high pressure.

Piston pumps of this type are relatively large, and can, therefore, be accommodated in confined underground workings only with difficulty.

Moreover, since different hydraulic rams often need to be pressurised with different amounts of hydraulic fluid (and/or with hydraulic fluid at different pressures), such pumps have to be provided with, for example, pressure-regulating valves, control valves and metering rams, and this results in a considerable total outlay.

When forming tunnels or galleries using tunnel drive shields such as knife shields, the only hydraulic fluid used hitherto is compressed oil.

This is because the axial-piston pumps available for delivering water-oil emulsions are too bulky in construction (and so require an excessive amount of space), and can only be accommodated with difficulty in the confined environment of underground workings. However, owing to the leakage and/or breaking of hydraulic pipes and conduits which cannot be avoided in the rough operating conditions of undergound workings, the use of oil as a hydraulic fluid leads to considerable contamination and danger when oil escapes.

Thus, for many years, there has existed a need, particularly in operations carried out in confined workings, to use a water-oil emulsion as the highpressure hydraulic fluid in tunnelling operations; and to provide a pump which has an output of between 300 and 500 bars but is of compact construction for such operations. A water-oil emulsion is environmentally acceptable and inexpensive, and so is particularly suitable for use in underground workings.

It has now been found that, provided certain criteria are met, rapid-action radial-piston pumps can be successfully used to delivery a water-oil emulsion at the required high pressures necessary for use with tunnel drive shields. Up to now, radial-piston pumps (which operate at speeds of at least 1 500 revolutions per minute and are of compact construction) have only been used with oil as the pressure medium.

Accordingly, the present invention provides a radial-piston pump for delivering a water-oil emulsion at high pressure, especially a water-oil emulsion whose oil content is less than 12%, the pump having a plurality of radial piston-andcylinder units, wherein each of the pistons has a maximum diameter of 12 millimetres, wherein the length of that part of each piston which is guided in its cylinder is at least two and a half times the diameter of that piston, and wherein each pistonand-cylinder unit is provided with an inlet valve having a flow cross-section of greater area than the cross-sectional area of the piston of that unit.

The invention also provides a radial-piston pump for delivering a water-oil emulsion at high pressure, especially a water-oil emulsion whose oil content is less than 12%, the pump comprising a housing, a shaft rotatably mounted in the housing, at least one set of radial piston-andcylinder units, the units of the or each set being symmetrically disposed about the shaft, each of the pistons being reciprocably driven within its cylinder by means of an eccentric cam fixed to the shaft, and each of the piston-and-cylinder units being provided with an inlet valve for controlling the flow of emulsion from the interior of the housing to that unit, wherein each of the pistons has a maximum diameter of 12 millimetres, wherein the length of that part of each piston which is guided in its cylinder is at least two and a half times the diameter of that piston, and wherein each inlet valve has a flow-cross-section of greater area than the cross-sectional area of the piston of that unit.

Preferably, each of the pistons has a diameter of between 6 and 10 millimetres, and the length of that part of each piston which is guided in its cylinder is at least three times the diameter of that piston.

The invention thus departs from the established view that rapid-action radial-piston pumps are not suitable for delivering a water-oil emulsion under high-pressure conditions, particularly when the pump shaft (together with its bearings) and the eccentric(s) acting on the pistons, rotates-within the emulsion supply chamber. It has been found, however, that, given the above-mentioned conditions, radial-piston pumps can be used with complete success with water-oil emulsions, although the compressibility factor of water is only about half that of oil, so that different operating conditions arise when a radial-piston pump is used with a water-oil emulsion.

The piston dimensions are important in considerably reducing internal leakage losses in the cylinders under the high-pressure conditions which prevail. This is because the overlapping zone (that is to say the length of the pistons which are guided in their cylinders) is increased, while the piston diameter is reduced (as compared with an oil pump of similar construction and capacity).

It is also essential that each of the inlet valves has a flow cross-section which is larger than the cross-section of its associated piston. When oil is used as the hydraulic fluid in a radial-piston pump, the inlet valves are, to some extent, damped by the oil which has a compressibility factor which is roughly twice that of a water-oil emulsion having a small proportion of oil. Because of the sharper sudden loadings (and particularly because of impacts suffered by the inlet valves), the use of a water-oil emulsion could lead to valve damage.

The smaller the piston diameter used, the smaller is the danger of the pistons tilting, and of sudden loading of the inlet valves. By reducing the piston diameter, and by increasing the valve flow-crosssections, these difficulties of water-oil emulsions can be overcome.

Advantageously, the shaft is rotatably supported within the housing by means of bearings, and the interior of the housing constitutes an emulsion supply chamber.

Preferably, the bearings supporting the shaft are ball bearings whose size is substantially twice the size of the ball bearings of an oil pump of similar construction and capacity, and the bearing are arranged within the emulsion supply chamber. In this way, the shaft bearings are rated for at least twice the number of operating hours as would be necessary if oil were used as the hydraulic fluid. In other words, the specific load on the shaft bearings of a radial-piston pump operating with a water-oil emulsion, is, at most, about half the specific load for that which would occur if oil were used as the hydraulic fluid. The use of ball bearings ensures that, under the heavy loads and high speeds of revolution, pitting can be avoided.

Where rollers are used for such bearings, pitting can occur as a result of vibration of the rollers and inadequate lubrication.

Preferably, the shaft has a diameter which is at least 1.4 times larger than that of the shaft of an oil pump of similar construction and capacity. This ensures smooth running of the pump under highpressure conditions, by ensuring that the pump shaft undergoes practically no deflection under operating conditions. Undesirable deflections of the pump shaft would transmit transverse forces to the pistons, which would lead to pitting of the pistons which would then be inadequately lubricated.

Each of the piston-and-cylinder units may be provided with an outlet valve, the outlet valves being larger thàn the outlet valves of an oil pump of similar construction and capacity. Similarly, the inlet valves should be larger than the inlet valves of an oil pump of simlar construction and capacity.

These valve size increases can be accomplished by appropriate selection of materials to suit the increase in size. In particular, materials of greater hardness and strength should be used.

Advantageously, there are a plurality of axially-spaced sets of piston-and-cylinder units.

Preferably, there are four groups of sets of units, the two inner groups each having two sets of units, and the two outer groups of units each having a single set of units. Conveniently, a respective duct plate is provided between each pair of adjacent groups of sets of units, each of the duct plates having internal ducting communicating with the outlets of the adjacent piston-and-cylinder units. The various outputs of the piston-and-cylinder units are brought together by way of the duct plates, which thereafter discharge the pressurised emulsion to hydraulic consumer units.

Advantageously, each of the pistons is provided with damping means for damping forces acting in the axial direction of that piston. The damping means prevent excessive pressure surges.

Preferably, each of the pistons is of two-part construction, the damping means of a given piston being sandwiched between the two parts of that piston. In this case, the two parts of each piston are connected together by connection means which permit a predetermined degree of axial movement therebetween.

The damping means of each piston may be made of rubber or plastics material. Where the pistons are of two-part construction, the damping means of each piston may also constitute a sealing element which acts as a piston ring.

The invention also provides a tunnel drive shield comprising a frame, a plurality of elongate members mounted in side-by-side relationship around the frame, each of the elongate members being movable exially relative to the frame, a plurality of hydraulic rams for advancing the elongate members relative to the frame, and a plurality of radial-piston pumps distributed along the periphery of the shield, each radial-piston pump serving topressurise a group of hydraulic rams, wherein each of the radial-piston pumps is as defined above.

A radial-piston pump constructed in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic transverse crosssection of the pump; Fig. 2 is an exploded perpsective view of the pump of Fig. 1; Fig. 3 is a part-sectional view of a first form of piston for use in the pump of Figs. 1 and 2; and Fig. 4 is a part-sectional view of a second form of piston for use in the pump of Figs. 1 and 2.

Referring to the drawings, Figs. 1 and 2 show a radial piston pump having a two-part housing 10, the two parts of the housing being fastened together by means of bolts (not shown). A central, axial pump shaft 11 extends within the housing 10, the pump shaft being rotatably supported by a means of ball bearings 12. The pump shaft 11 is provided with a plurality of eccentric cams 1 3 (one of which can be seen in Fig. 1), the cams being fixed to the pump shaft. Associated with each of the cams 13 is at least one set of cylinder blocks 14. As shown in Fig. 1, the seven cylinder blocks 14 of each set are radially positioned with respect to the pump shaft, and are equispaced. A radial piston 1 5 is associated with each of the cylinder blocks 14, the pistons radiating from the shaft 11 in the manner of the spokes of a wheel. Each of the pistons 1 5 is reciprocated within its cylinder block 14 by engagement with the periphery of the associated cam 13, the pistons being biassed inwardly into engagement with their cam by means of respective coil springs 1 6. A chamber 1 7 is formed within the hollow interior of the pump housing 10, the chamber being supplied with a water-oil emulsion via an inlet port 1 9 provided in the housing. As the chamber 1 7 surrounds the shaft 11, the bearings 12, the cams 13 and the springs 16, all these parts are washed by the emulsion so that a certain cooling effect is achieved.

The piston 1 5 of each cylinder block 1 4 is reciprocal within a cylinder bore 20 of that block, Each cylinder block 14 is provided with a nonreturn valve 21 at the outer end of the cylinder bore 20 of that cylinder block. Each of the nonreturn valves 21 is constituted by a spring-loaded ball valve, through which emulsion is drawn, from the chambers 1 7, during the suction stroke of the associated piston 1 5. The suction strokes of the pistons 1 5 are the radially-inward strokes, and are effected by the springs 1 6. Each cylinder block 1 4 also has a transverse bore 22 which communicates with the cylinder bore 20, and which accommodates a pressure-relief valve (not shown).The pressure-relief valve opens, to eject pressurised emulsion through the bore 22, when the associated piston 1 5 executes a compression stroke. The compression strokes of the pistons 1 5 are radially-outward strokes, and are effected by the associated cam 1 3 The pressure-relief valves are also constituted by spring-loaded ball valves.

As shown in Fig. 2, the pump has a number of axially-spaced groups 23 and 24 of cylinder blocks 14. The two inner groups 23 of each have two sets of cylinder blocks 14, and the two outer groups 24 each have one set of cylinder blocks 14. A respective duct plate 25 is arranged between each pair of adjacent groups. The shaft 11 extends through the duct plates 25, and is mounted thereon by the bearings 12. Each of the duct plates 25 is provided with internal ducts (not shown), which communicate with the transverse bores 22 of the adjacent cylinder blocks 14, the internal ducts serving to carry away the pressurised emulsion. The internal ducts terminate, at the periphery of the plates 25, at ports 26. A collector bar 27 is provided for taking up the pressurised emulsion leaving the ports 26.

The collector bar 27 has inlet ports (not shown) and internal ducting (shown in dahed lines in Fig.

2) for leading the pressurised emulsion to an outlet port P, from where the pressurised emulsion is directed to, for example, hydraulic rams.

To enable the radial piston pump described above to be operated at high pressures (that is to say at delivery pressures of 300 to 500 bars) using a water-oil emulsion, the emulsion having an oil content which is less than 12% and preferably is between 8 and 10%, the pump must have the following characteristics. The diameter of each of the pistons should be at most 1 2 millimetres, and preferably between 6 and 10 millimetres. The length of each piston 1 5 that is guided in its cylinder bore 20 should be at least two and a half times, and preferably at least three times, the diameter of that piston. Each of the valves 21 should have a larger flow cross-section than that of the pressure-relief valve in the associated bore 22, and the flow cross-section of the valve 21 should be greater than the crosssectional area of the associated piston 1 5.

Moreover, the ball bearings 1 2 which support the shaft 11 should be at least two times greater than those of an oil pump of similar construction and capacity. Similarly, the shaft 11 should have a diameter 1.4 times greater than that of an oil pump of similar construction and capacity. The inlet (not return) valves 21 and the outlet (pressure-relief) valves of the cylinder blocks 14 should be made of high-strength, hard materials.

Preferably, these valves should be larger than the equivalent valves of an oil pump of similar construction and capacity.

It is also preferable to provide damping means between each of the pistons 1 5 and its associated cam 13. The damping means act to prevent excessively large impacts such as can occur under high-pressure conditions when a water-oil emulsion is used. Figs. 3 and 4 show pistons incorporating two forms of suitable damping means.

As shown in Fig. 3, each of the pistons 1 5 may be of multi-part construction, having a first piston part 15', a second piston part 15" and a disc 28 which constitutes the damping means. The second piston part 15" has a central, cylindrical recess which houses the first piston part 15', the disc 28 being sandwiched between the end of the first piston part and the base of the recess in the second piston part. The base of the recess is formed with a concave depression 29, into which the disc 28 can deform during compression strokes of the piston. The first piston part 1 5' has a domed head 30 which co-operates with the associated eccentric cam 1 3. The two piston parts 15' and 1 5" are interconnected by means of a groove-and-circlip connection 31.This connection 31 permits a predetermined amount of axial play between the two piston parts 15' and 1 5", and so permits the required degree of damping.

The piston 1 5 shown in Fig. 4 is also of multipart construction, having a first piston part 15', a second piston part 1 5", and an annular damping member 28'. The first piston part 1 5' has an axial extension 32 of reduced cross-section, the extension 32 engaging within a central, cylindrical recess 33 provided in the second piston part 1 5".

The annular damping member 28' is sandwiched between the end face 35 of the second piston 1 5" and an annular shoulder 34 formed on the first piston part 15' in the region where the extension 32 merges with the maize body of the first piston part. As with the embodiment of Fig. 3, the first piston part 15' has a domed head 30 which cooperates with the associated eccentric cam 1 3.

similarly, the two piston parts 15' and 15" are interconnected by means of a groove-and-circlip connection 31 which permits a predetermined amount of axial play. During the pressure stroke of the piston 15, the annular damping member 28' is axially compressed. At the same time, it is radially deformed, thereby forming a sealing element which seals the piston 1 5 against the associated cylinder bore 20.

Claims

1. A radial-piston pump for delivering a wateroil emulsion at high-pressure, especially a wateroil emulsion whose oil content is less than 12%, the pump having a plurality of radial piston-andcylinder units, wherein each of the pistons has a maximum diameter of 12 millimetres, wherein the length of that part of each piston which is guided in its cylinder is at least two and a half times the diameter of that piston, and wherein each pistonand-cylinder unit is provided with an inlet valve having a flow cross-section of greater area than the cross-sectional area of the piston of that unit.

2. A radial-piston pump for delivering a wateroil emulsion at high pressure, especially a wateroil emulsion whose oil content is less than 12%, the pump comprising a housing, a shaft rotatably mounted in the housing, at least one set of radial piston-and-cylinder units, the units of the or each set being symmetrically disposed about the shaft, each of the pistons being reciprocably driven within its cylinder by means of an eccentric cam fixed to the shaft, and each of the piston-andcylinder units being provided with an inlet valve for controlling the flow of emulsion from the interior of the housing to that unit, wherein each of the pistons has a maximum diameter of 12 millimetres, wherein the length of that part of each piston which is guided in its cylinder is at least two and a half times the diameter of that piston, and wherein each inlet valve has a flow cross-section of greater area than the cross-sectional area of the piston of that unit.

3. A radial-piston pump as claimed in claim 2, wherein each of the pistons has a diameter of between 6 and 10 millimetres.

4. A radial-piston pump as claimed in claim 2 or claim 3, wherein the length of that part of each piston which is guided in its cylinder is at least three times the diameter of that piston.

5. A radial-piston pump as claimed in any one of claims 2 to 4, wherein the shaft is rotatably supported within the housing by means of bearings, and wherein the interior of the housing constitutes an emulsion supply chamber.

6. A radial-piston pump as claimed in claim 5, wherein the bearings supporting the shaft are ball bearings whose size is substantially twice the size of the ball bearings of an oil pump of similar construction and capacity.

7. A radial-piston pump as claimed in claim 5 or claim 6, wherein the bearings are arranged within the emulsion supply chamber.

8. A radial-piston pump as claimed in any one of claims 2 to 7, wherein the shaft has a diameter which is at least 1.4 times larger than that of the shaft of an oil pump of similar construction and capacity.

9. A radial-piston pump as claimed in any one of claims 2 to 8, wherein each of the piston-andcylinder units is provided with an outlet valve.

10. A radial-piston pump as claimed in claim 9, wherein the outlet valves are larger than the outlet valves of an oil pump of similar construction and capacity.

11. A radial-piston pump as claimed in any one of claims 2 to 10, wherein the inlet valves are larger than the inlet valves of an oil pump of similar construction and capacity.

12. A radial-piston pump as claimed in any one of claims 2 to 11 , wherein there are a plurality of axially-spaced sets of piston-and-cylinder units.

1 3. A radial-piston pump as claimed in claim 12, wherein there are four groups of sets of units, the two inner groups each having two sets of units, and the two outer groups of units each having a single set of units.

14. A radial-piston pump as claimed in claim 13, wherein a respective duct plate is provided between each pair of adjacent groups of sets of units, each of the duct plates having internal ducting communicating with the outlets of the adjacent piston-and-cylinder units.

1 5. A radial-piston pump as claimed in any one of claims 2 to 14, wherein each of the pistons is provided with damping means for damping forces acting the axial direction of that piston.

1 6. A radial-piston pump as claimed in claim 1 5, wherein each of the pistons is of two-part construction, the damping means of a given piston being sandwiched between the two parts of that piston.

1 7. A radial-piston pump as claimed in claim 1 5 or claim 16, wherein the damping means of each piston is made of rubber or-plastics material.

1 8. A radial-piston pump as claimed in claim 1 6 or claim 17, wherein the two parts of each piston are connected together by connection means which permit a predetermined degree of axial movement therebetween.

19. A radial-piston pump as claimed in any one of claims .16 to 18, wherein the damping means of each piston also constitutes a sealing element which acts as a piston ring.

20. A radial-piston pump substantial as hereinbefore described with reference to, and as illustrated by, Figs. 1 to 3 or Figs. 1, 2 and 4 of the a accompanying drawings.

21. A tunnel drive shield comprising a frame, a plurality of elongate members mounted in side-by- side relationship around the frame, each of the elongate members being movable axially relative to the frame, a plurality of hydraulic rams for advancing the elongate members relative to the frame, and a plurality of radial-piston pumps distributed along the periphery of the shield, each radial-piston pump serving to pressurise a group of hydraulic rams, wherein each of the radialpiston pumps is as claimed in any one of claims 1 to 20.