Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B1/00—Multi-cylinder machines or pumps characterised by number or arrangement of cylinders
  • F04B1/12—Multi-cylinder machines or pumps characterised by number or arrangement of cylinders having cylinder axes coaxial with, or parallel or inclined to, main shaft axis
  • F04B1/122—Details or component parts, e.g. valves, sealings or lubrication means
  • F04B1/124—Pistons
  • F04B1/126—Piston shoe retaining means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B53/00—Component parts, details or accessories not provided for in, or of interest apart from, groups F04B1/00 - F04B23/00 or F04B39/00 - F04B47/00
  • F04B53/14—Pistons, piston-rods or piston-rod connections

Definitions

• the present invention relates to a method of assembling a piston and shoe of a hydraulic pump, and a piston and shoe assembly.
• a piston pump typically comprises a barrel that has a number of bores for receiving pistons therein.
• the pistons are arranged such that axial displacement within the corresponding bore causes either compression or suction dependent on the stroke of the piston.
• the pistons are held by shoes at one end that translate along the surface of an angle block, e.g. an inclined plate. Rotation of the barrel and shoes cause the pistons to move axially within the bores of the barrel as the shoes move axially inwards or outwards due to the inclination of the angle block.
• an angle block e.g. an inclined plate.
• the pistons may have a piston sphere that is placed into an open socket of the shoe, which is then crimped about the piston sphere to secure the piston sphere in place.
• the crimped portions of the shoe can be a point of weakness that can fail in use.
• a method of assembling a piston and shoe of a hydraulic pump comprising: inserting a shaft of the piston through an aperture of the shoe such that it extends through to the other side until a piston head of the piston is seated in the shoe.
• the method comprises inserting a plug into the shoe such that the piston head is held between the shoe and the plug.
• the method comprises installing a piston sleeve onto the shaft of the piston.
• the method comprises installing a fixing into the piston and piston sleeve to secure the piston and piston sleeve together.
• the piston sleeve is a first piston sleeve and the method comprises: removing the fixing from the piston and first piston sleeve; removing the first piston sleeve from the shaft of the piston; and installing a second piston sleeve onto the shaft of the piston.
• the second piston sleeve is of a greater or smaller cross section than the first piston sleeve.
• a method of disassembling a piston and shoe of a hydraulic pump comprising: passing a shaft of the piston through an aperture of the shoe to thereby decouple a piston head of the piston from the shoe.
• a piston and shoe assembly for a hydraulic pump, the assembly comprising: a piston comprising a piston shaft and a piston head; and a shoe comprising an aperture, wherein the piston shaft is sized such that it can pass through the shoe aperture and the piston head is sized such that it cannot pass through the shoe aperture.
• the piston and shoe assembly comprises a plug at least partially located within the shoe and arranged to hold the piston head in the shoe.
• the piston and shoe assembly comprises a piston sleeve along the piston shaft.
• the piston and shoe assembly comprises a fixing arranged to secure the piston sleeve to the piston shaft.
• the piston comprises a piston inner passageway and the plug comprises a plug inner passageway, the piston inner passageway and plug inner passageway arranged in fluid communication.
• the plug inner passageway comprises an enlarged opening for receiving fluid communication from the piston inner passageway.
• the piston head comprises a spherical portion
• the piston shaft has a circular cross-section and the shoe aperture is of circular cross-section
• the diameter of the spherical portion of the piston head is greater than the diameter of the piston shaft and the shoe aperture has a diameter that is greater than the diameter of the piston shaft and smaller than the diameter of the piston head.
• a hydraulic pump comprising the piston and shoe assembly according to the third aspect.
• a method of assembling a piston and shoe of a hydraulic pump comprising: inserting a shaft of the piston through an aperture of the shoe such that it extends through to the other side until a piston head of the piston is seated in the shoe.
• the piston and shoe can be assembled without requiring deformation of the shoe such as crimping.
• the method may not comprise deforming, reshaping, bending or crimping the shoe to secure the piston head.
• a method of assembling a piston and shoe is provided that does not require deformation of the shoe, such as crimping of the shoe.
• the method can provide a piston and shoe assembly of enhanced strength, durability and wear resistance because the shoe can be formed of a material that does not need to be deformable.
• the shoe may be formed of stainless steel for enhanced strength and the plug can be formed of copper alloy, such as bronze, for sliding and wear resistance properties, though any suitable material(s) may be used in practice.
• the method may also increase the ease with which the piston and shoe can be assembled and hence reduce assembly costs.
• Inserting the shaft of the piston through the aperture of the shoe may comprise passing the length of the piston shaft through the aperture.
• the piston may begin on a first side of the shoe aperture and be passed through the aperture of the shoe such that a majority of or the entirety of the piston shaft is on the second side of the aperture.
• the piston head may remain on the first side of the shoe aperture.
• the shaft is passed through the shoe.
• the piston head may be sized such that it cannot pass through the aperture.
• the seating of the piston head in the shoe may comprise the piston head abutting a shoulder of the shoe aperture.
• the piston as a whole therefore may pass partially through the shoe but not entirely through due to the piston head.
• the piston head and the shoe may therefore prevent relative axial displacement of the piston in at least one direction by the piston head being seated in the shoe.
• the piston head and piston shaft may be linked by a piston neck.
• the piston neck may be narrower than the piston head and the piston shaft.
• the piston neck may transition from its most narrow at the piston head to its widest point at the piston shaft.
• the piston neck may taper from a narrow diameter at the piston head to a wider diameter at the piston shaft.
• the piston neck may be a connecting element between the piston shaft and the piston head, and may serve to delineate those two elements. Any suitable form of piston neck may be employed as required.
• the neck may pass through the aperture, at least partially.
• the piston neck may be configured to enable sufficient rotation of the shaft relative to the shoe.
• the piston neck diameter and/or piston neck taper may be configured to position the piston shaft appropriately relative to the shoe in the event that the piston and shoe are assembled in a hydraulic pump, e.g. when aligned with or pressed against an angle block.
• the piston neck may be configured to ensure the correct angle of the shoe with respect to the piston in the event that the piston and shoe are adjacent or against an angle block, for example when the piston and shoe are assembled in a hydraulic pump.
• the method may comprise assembling a plurality of pistons and shoes of a hydraulic pump.
• the method may comprise inserting a shaft of each of the plurality of pistons through respective apertures of the plurality of shoes until a piston head of each piston is seated in each shoe such that the pistons extend through to the other side of the shoes.
• the method may comprise inserting a plug into the shoe such that the piston head is held between the shoe and the plug.
• the plug may allow the piston to be maintained in place and may limit backlash (e.g. axial movement of the piston head relative to the shoe) in use to ensure the correct stroke of the piston.
• the plug may limit or eliminate fluid leakage from inside of the piston assembly to the outside. Limiting backlash and/or leakage may increase the efficiency of a hydraulic pump.
• the method may comprise adjusting the plug to reduce backlash of the piston.
• the method may comprise adjusting the plug to adjust pressure balancing and lubrication functions of the piston and shoe.
• the method may therefore comprise securing the piston, via the piston head, to the shoe by restricting the piston head between the shoe aperture and the plug. Inserting the plug into the shoe may prevent the piston shaft from passing back through the aperture.
• the method may comprise securing the plug to the shoe e.g. by a press fit, a friction fit, or any suitable fixing means, to thereby ensure that piston - and specifically the piston head - is held securely within the shoe.
• the method may comprise installing a piston sleeve onto the shaft of the piston.
• the method may comprise increasing the working diameter of the piston shaft via the addition of the piston sleeve.
• the method may use a standard size piston for use with a number of differing bore diameters of different pumps by installing correspondingly sized piston sleeves onto the piston shaft.
• the resulting shaft assembly e.g. the piston shaft and the piston sleeve, may have a cross section that cannot pass through the shoe aperture.
• different materials may be used for the piston shaft and piston sleeve. The properties of the sleeve can therefore be different to those of the shaft, and the shaft may therefore be e.g. less durable than the sleeve.
• the method may comprise installing a fixing into the piston and piston sleeve to secure the piston and piston sleeve together.
• the method may comprise joining the piston and piston sleeve together.
• Any suitable fixing may be used.
• the fixing may be a pin.
• the pin may be a stop pin.
• a plurality of fixings may be used.
• the piston and piston sleeve may comprise corresponding openings and the step of installing the fixing may comprise installing the fixing into the corresponding openings of the piston and piston sleeve.
• the opening in the piston may be in the piston shaft.
• the method may comprise inserting the fixing through the piston sleeve and piston shaft, to thereby fix the piston sleeve to the piston shaft.
• the method may comprise inserting the shoe into a shoe holder.
• the method may comprise inserting the piston shaft into a barrel of a hydraulic pump.
• the piston sleeve may be a first piston sleeve and the method may comprise: removing the fixing from the piston and first piston sleeve; removing the first piston sleeve from the shaft of the piston; and installing a second piston sleeve onto the shaft of the piston.
• the method may provide a means of reconfiguring the piston without requiring disassembly of the piston from the shoe.
• a damaged piston sleeve may be replaced without requiring disassembly of the piston from the shoe.
• the method may comprise changing the piston sleeve to a second piston sleeve different to the first piston sleeve.
• the method may therefore comprise re-sizing the working size of the piston of the hydraulic pump.
• the method may comprise repairing the pump by replacing the piston sleeve.
• the method may therefore be a method of repairing a hydraulic pump, and/or reconfiguring a hydraulic pump.
• the plug may be replaced to repair the pump or reconfigure the balancing according to the piston sleeve cross section.
• the second piston sleeve may be of a greater or smaller cross section than the first piston sleeve.
• the method may provide a means of reconfiguring the piston and shoe for use in a hydraulic pump having a different bore diameter without requiring disassembly of the piston from the shoe.
• the method may comprise assembling a hydraulic pump.
• the hydraulic pump may comprise an angle block that provides an inclined surface and the method may comprise positioning the shoe on the inclined surface of the angle block.
• the method may comprise lubricating the angle block with fluid supplied from within a barrel of the pump via fluid passageways within the piston, shoe and optionally the plug.
• the method may comprise separating the shoe from the angle block by providing pressure communication from within a barrel of the pump to a region between the angle block and shoe via the fluid passageways within the piston, shoe and optionally the plug. The separation may be by a layer (e.g. a very thin layer) of lubricant (e.g. oil) to lubricate the contact area.
• lubricant e.g. oil
• the method according to the first aspect of the invention, and optionally and of the optional features of the first aspect described, may be repeated to assemble a plurality of pistons and shoes of a hydraulic pump.
• a method of disassembling a piston and shoe of a hydraulic pump comprising: passing a shaft of the piston through an aperture of the shoe to thereby decouple a piston head of the piston from the shoe.
• the piston and shoe can be disassembled without requiring deformation of the shoe such as crimping.
• the method may not comprise deforming, reshaping, bending or crimping the shoe to decouple the piston head from the shoe.
• a method of disassembling a piston and shoe is provided that does not require deformation of the shoe, such as crimping of the shoe. Therefore, the method can provide a piston and shoe assembly of enhanced strength and durability because the shoe can be formed of a material that does not need to be deformable and is more resistant to wear. The method may also increase the ease with which the piston and shoe can be both assembled and disassembled and hence reduce the associated costs.
• Passing the shaft of the piston through the aperture of the shoe may comprise passing the length of the piston shaft through the aperture.
• the piston shaft may begin on a first side of the shoe aperture and be passed through the aperture of the shoe such that a majority of or the entirety of the piston shaft is on the second side of the aperture.
• the piston head may begin and remain on the second side of the shoe aperture.
• the method of disassembling a piston and shoe of a hydraulic pump may comprise the reverse of the method of assembling a piston and shoe of a hydraulic pump described in relation to the first aspect.
• the disassembly may allow maintenance, repair, and/or cleaning of components of the hydraulic pump.
• the method may be a method of maintenance of the hydraulic pump comprising disassembling as described herein.
• the method of disassembling the piston and shoe of a hydraulic pump may comprise removing a plug from the shoe such that the piston head can be removed from the shoe.
• the method may comprise releasing the piston from the shoe by removing the restriction provided by the piston head being arranged between the shoe aperture and the plug. Removing the plug from the shoe may allow the piston shaft to pass through the aperture.
• the method may comprise removing a piston sleeve from the shaft of the piston.
• the method may comprise decreasing the working diameter of the piston shaft via the removal of the piston sleeve.
• removal of the piston sleeve may allow the piston shaft to pass through the aperture, which may not be otherwise possible with the working diameter of the piston shaft with the piston sleeve attached.
• the method may use a standard size piston for use with a number of differing bore diameters of different pumps by installing correspondingly sized piston sleeves onto the piston shaft.
• the resulting shaft assembly e.g. when the piston shaft and the piston sleeve are assembled, may have a cross section that cannot pass through the shoe aperture.
• the method may comprise removing a fixing from the piston and piston sleeve to release the piston sleeve from the piston.
• the method may comprise removing the shoe from a shoe holder.
• the shoe may be configured to engage the shoe holder in an abutting arrangement. Removing the shoe from the shoe holder may comprise first passing the piston shaft through the shoe holder.
• the method may comprise removing the piston shaft from a barrel of a hydraulic pump.
• the method according to the second aspect of the invention may comprise the method as recited herein according to the first aspect of the invention.
• a piston and shoe assembly for a hydraulic pump, the assembly comprising: a piston comprising a piston shaft and a piston head; and a shoe comprising an aperture, wherein the piston shaft is sized such that it can pass through the shoe aperture and the piston head is sized such that it cannot pass through the shoe aperture.
• the piston may therefore be secured to the shoe by passing the piston shaft through the shoe aperture.
• the piston and shoe can be assembled without requiring deformation of the shoe such as crimping.
• the shoe may be made of stronger more durable materials, which would not be possible where deformation, such as crimping, is required to secure the piston to the shoe.
• the sizing of the piston shaft, piston head, and shoe aperture improves the ease with which the piston and shoe can be assembled.
• the piston head may have a cross-section that is greater than the cross-section of the piston shaft.
• the shoe aperture may have a cross section that is greater than the cross-section of the piston shaft and smaller than the cross section of the piston head.
• the piston shaft may be configured to pass through the shoe aperture during assembly and the piston head may be configured not to pass through the shoe aperture during assembly.
• the piston may be retained by the shoe as a result of the piston head being unable to pass through the shoe aperture.
• the piston head may have a diameter that is greater than the diameter of the piston shaft.
• the shoe aperture may have a diameter that is greater than the diameter of the piston shaft and smaller than the diameter of the piston head.
• the piston and shoe assembly may comprise a plug at least partially located within the shoe and arranged to hold the piston head in the shoe.
• the plug may allow the piston to be maintained in place and limit backlash in use of the piston and shoe assembly to ensure the correct stroke of the piston.
• the plug may limit or eliminate leakage from inside of the piston assembly to the outside. Limiting backlash and/or leakage may increase the efficiency of a hydraulic pump.
• the plug may be adjustable to reduce backlash of the piston.
• the plug may be machined to adjust its dimensions.
• the piston may be secured, via the piston head, between the shoe aperture and the plug.
• no deformation, such as crimping, is required to secure the piston and shoe together.
• the plug may restrict the piston sphere axially.
• the plug may comprise a plug face for sliding engagement with an angle block of the hydraulic pump.
• the plug and shoe may be formed of differing materials.
• the material of the plug and shoe can each be selected as appropriate to balance wear and cost considerations.
• the shoe may comprise a bore that is of greater diameter than the shoe aperture.
• the shoe aperture may be formed as a constriction of the bore.
• the plug may have a diameter configured to provide e.g. an interference or friction fit with the bore of the shoe. The plug may therefore be secured to the shoe via friction. However, any suitable securement may be used.
• the plug may be configured to permit rotational movement of the piston sphere in the shoe.
• the piston and shoe being permitted to rotate with respect to one another enables, when assembled in a hydraulic pump, that they can rotate whilst following the face of an angle block and the shaft of the piston can travel inside a respective barrel bore which causes pump displacement.
• imperfect alignment of the piston in use can be tolerated by allowing the piston sphere to rotate as required.
• the piston and shoe assembly may comprise a piston sleeve along the piston shaft.
• the piston sleeve may be disposed about the piston shaft.
• the piston sleeve may be an annular member.
• the piston sleeve may have an external cross-section that is greater than the cross-section of the piston head.
• the piston sleeve may have an external diameter that is greater than the diameter of the piston head.
• the piston sleeve may have an internal diameter that is equal the diameter of the piston shaft e.g. so that it fits thereupon.
• a standard size piston may be used in the piston and shoe assembly and the piston and shoe assembly can be configured for various hydraulic pump designs by selecting an appropriately size piston sleeve. For example, for a smaller capacity hydraulic pump with smaller bores in the barrel, a smaller cross section piston sleeve may be selected than would be selected for a larger capacity hydraulic pump with larger bores in the barrel.
• the piston sleeve may be of a different material to the piston, the shoe, the plug and/or the barrel of the hydraulic pump.
• the piston sleeve material may be selected based on the material of the barrel of the hydraulic pump.
• the piston sleeve material may be selected based on the hydraulic fluid that is to be used in the hydraulic pump the piston and shoe will be assembled in.
• the piston sleeve material may be selected based on the use conditions. For example, the piston sleeve material may be selected based on the hydraulic pump's intended displacement, the hydraulic pumps max rpm, and/or operating temperature.
• the piston and shoe assembly may comprise a fixing arranged to secure the piston sleeve to the piston shaft.
• the piston shaft and piston sleeve may therefore act as one piston shaft of greater dimension than the piston shaft itself.
• the fixing may be a pin.
• the pin may be a stop pin.
• the piston may comprise a piston inner passageway and the plug may comprise a plug inner passageway, the piston inner passageway and plug inner passageway may be arranged in fluid communication.
• the piston inner fluid passageway and the plug inner passageway may allow for lubrication of the piston head for well-functioning operation and reduced or limited wear.
• the piston inner passageway and the plug inner passageway may be arranged such that, in use, hydraulic force balancing is provided between the force acting on the piston in the barrel of the hydraulic pump and the force acting on the piston head at the shoe.
• the piston inner passageway allows pressure communication between the barrel of the pump and the head end of the piston. In the event that pressure in the barrel is positive the pressure will be balanced at the both sides of the piston due to the piston inner passageway. This allows the force acting on the piston to be reduced as there will be counteracting forces at each end of the piston due to the pressure. In the event that the pressure within the barrel is negative there is only a traction force that pulls the piston in a direction away from the shoe. For the same piston shaft size, the force acting on the piston will be the same.
• the sizing of the shoe, its aperture and/or the machining process provide a greater confidence on the assembly strength than using a crimping process to secure the piston to the shoe.
• the risk of damage to the shoe can be reduced as the shoe can be sized and machined to accommodate the force acting to pull or push the piston head. In short, the shoe does not need to be crimped.
• the plug inner passageway may comprise an enlarged opening for receiving fluid communication from the piston inner passageway.
• the enlarged opening may continue to allow fluid communication between the piston and plug in the event that the piston and shoe are angled relative to one another and/or in the event that the angle varies.
• the enlarged opening may ensure lubrication around the piston head despite the angle of the piston and plug.
• the enlarged opening may be enlarged relative to the portion of the piston inner passageway that is adjacent to the enlarged opening.
• the enlarged opening may advantageously continue to allow fluid communication in the event that the piston inner passageway and plug inner passageway have a misalignment or in the event that the piston head pivots or rotates in the shoe (e.g. during operation of the pump and the angle caused by the shoe on the angle block and the piston within the barrel).
• the plug inner passageway may comprise an outlet portion for outputting fluid to an angle block of a hydraulic pump.
• the outlet portion and the plug face may be configured such that in use a film of lubricant may be produced on the angle block of a hydraulic pump.
• the outlet portion may have an outlet diameter that is proportioned relative to the plug face diameter such that a film of lubricant may be produced on the angle block of a hydraulic pump.
• the film of lubricant may be a thin film.
• the diameters of the outlet portion and plug face may be selected according to the pump displacement and the performances desired.
• the piston head may comprise a spherical portion, the piston shaft may have a circular cross-section and the shoe aperture may be of circular cross-section, and the diameter of the spherical portion of the piston head may be greater than the diameter of the piston shaft and the shoe aperture may have a diameter that is greater than the diameter of the piston shaft and smaller than the diameter of the piston head.
• the shoe may comprise a hemispherical recess for receiving the piston head.
• the shoe aperture may be formed in the hemispherical recess.
• the hemispherical recess may form the (or part of the) constriction of the shoe bore.
• the plug may comprise a hemispherical recess for receiving the piston head.
• the hemispherical recess of the shoe and the hemispherical recess of the plug may enclose or partially enclose the piston head.
• the hemispherical recess of the shoe and the hemispherical recess of the plug may allow the piston head, and thereby the piston, to pivot.
• the piston head, shoe and the plug may be arranged such that a gap may be present between the piston head and the hemispherical recess of the plug.
• the gap may be configured to receive fluid for lubrication.
• Advantageously wear may be reduced as the piston head pivots.
• the gap may be configured to allow the piston head to pivot within the shoe and the plug.
• the plug may be rectified, e.g. machined, to alter or adjust the dimension of the gap.
• the face of the plug in contact with the shoe may be rectified to alter or adjust the dimension of the gap.
• a hydraulic pump comprising the piston and shoe assembly according to the second aspect, optionally including any of the optional features of the second aspect.
• the method as described herein with reference to the first aspect of the invention and/or the second aspect of the invention may comprise providing and/or assembling an assembly as described herein with reference to the third aspect of the invention, and/or a hydraulic pump as described here with reference to the fourth aspect of the invention.
• a method of assembling a piston and shoe of a hydraulic pump comprising securing a piston head of the piston within the shoe by inserting a plug into the shoe.
• the method may comprise holding the piston head between the shoe and plug to thereby secure the piston relative to the shoe.
• the method may comprise any of the features recited herein with reference to any other aspect of the invention.
• FIG. 1 shows a hydraulic pump 10 in cross section.
• the hydraulic pump 10 has a motor 12, a motor shaft 14, a barrel 60, a plurality of piston and shoe assemblies 100, a shoe holder 80, a shoe holder biasing mechanism 90 and an angle block 120.
• the motor 12 is configured to rotate the barrel 60 via the motor shaft 14.
• the barrel 60 comprises a plurality of bores 62 that the pistons 20 of the piston and shoe assemblies 100 are arranged within. Translation of a piston 20 within the corresponding bore 62 causes fluid to be drawn into the bore 62 and/or be discharged therefrom, e.g. during a suction stroke or a discharge stroke of the piston 20 respectively.
• the shoe holder 80 is arranged to position the plurality of piston and shoe assemblies 100 such that the pistons 20 are spaced apart and are aligned with corresponding bores 62 of the barrel 60.
• the shoe holder biasing mechanism 90 biases the shoe holder towards the angle block 120.
• the shoes 40 of the piston and shoe assemblies 100 are arranged on the angle block 120, e.g. a block that provides an inclined surface.
• the motor 12 rotates the barrel 60, which causes the piston and shoe assemblies 100 and the shoe holder 80 to rotate therewith. In figure 1 , this rotation is into and out of the page.
• the pistons 20 translate in the corresponding bores 62 due to the inclination of the surface of the angle block 120. This translation provides suction as the piston 20 translates in a first direction and discharge as the piston 20 translates in a second direction.
• Figure 2 shows a cross-section of a piston and shoe assembly 100 that requires crimping to secure the piston 20 within the shoe 40.
• the piston and shoe assembly 100 comprises a piston 20 and a shoe 40.
• the piston 20 has a piston shaft 22 and a piston sphere 24 forming a head of the piston 20.
• the shoe 40 has a shoe face 42 for sliding engagement with an angle block 120.
• the shoe 40 has a socket portion 44 for receiving the piston sphere 24.
• the shoe 40 has a lip 46 that is deformed by crimping about the piston sphere 24 such that the shoe 40 retains the piston sphere 24 in the socket portion 44.
• the piston sphere 24 is first located within the open socket portion 44 of the shoe 40 and then the lip 46 is crimped about the piston sphere 24 to substantially close the socket portion 44 and thereby couple the two together.
• the piston and shoe assembly 100 can then be inserted into the wider components of a pump 10 such as that of Figure 1 . More specifically, and as shown in Figure 2 , the piston shaft 22 is inserted into a corresponding bore 62 of a barrel 60 of the pump 10. The shoe 40 is installed between a shoe holder 80 and an angle block 120.
• the piston 20 comprises a fluid passageway 26 that is configured to provide fluid communication from the bore 62 to a corresponding fluid passageway 48 in the shoe 40.
• the fluid passageway 48 in the shoe 40 extends from the socket portion 44 to an opening 50 in the shoe face 42.
• the fluid passageway 26 and the fluid passageway 48 permit a thin film of fluid to be produced on the angle block 120 at the shoe face 42 for the purpose of lubrication.
• the fluid passageway 48 also comprises an enlarged opening 52 toward the socket portion 44 and is arranged to permit lubrication of the piston sphere 24.
• the enlarged opening 52 also continues to permit fluid communication between the fluid passageway 48 of the shoe 40 and the fluid passageway 26 of the piston 20 in the event that the piston 20 and shoe 40 are angled or rotate with respect to one another.
• Figures 3 and 4 show a piston and shoe assembly 110 according to an embodiment of the invention.
• Figure 3 shows the piston and shoe assembly 110 angled as may be typical in use.
• Figure 4 shoes the piston and shoe assembly 110 with the piston 200 and shoe 400 aligned for the purposes of illustrating the relative diameters of the components.
• the piston and shoe assembly 110 comprises a piston 200 and a shoe 400.
• the piston 200 has a piston shaft 220 and a piston sphere 240.
• the shoe 400 has an aperture 410.
• the piston shaft 220 has a diameter ⁇ 1 , that is less than the diameter, ⁇ 2 , of the aperture 410.
• the piston sphere 240 has a diameter, ⁇ 3 , that is greater than the diameter, ⁇ 2 , of the aperture 410.
• the piston 200 and more specifically the piston shaft 220, can be inserted through the shoe 400, in a direction from left to right when viewed in Figure 3 or 4 , because the piston shaft 220 is of smaller diameter than the aperture 410.
• the piston sphere 240 cannot pass through the aperture 410 because it has a greater diameter than the aperture 410.
• the piston 200 can be retained by the shoe 400, in a direction from left to right when viewed in Figure 3 or 4 , due to the relative dimensions of the piston sphere 240 and the aperture 410.
• the piston and shoe assembly 110 comprises a plug 420.
• the plug 420 has a plug face 422 for sliding engagement with the angle block 120.
• the plug 420 is installed within the shoe 400 e.g. by friction fit and is configured to retain the piston sphere 240 in a direction from right to left when viewed in Figure 3 .
• the piston 200 is therefore secured to the shoe 400 by the combination of the piston sphere 240 having a greater diameter than aperture 410, and the plug 420, and therefore any translational movement of the shoe 400 is imparted to the piston 200.
• the shoe 400 therefore does not need to be deformed (e.g. by crimping) to retain the piston 200.
• the piston 200 comprises a fluid passageway 226 that is configured to provide fluid communication from the bore 62 to a corresponding fluid passageway 428 in the plug 420.
• the fluid passageway 226 and the fluid passageway 428 permit a thin film of fluid to be produced on the angle block 120 at the plug face 422 for the purpose of lubrication.
• the fluid passageway 226 and the fluid passageway 428 also permits fluid to be provided to the piston head 240 for the purpose of lubricating the piston head 240 in the shoe 400 and plug 420.
• the fluid passageway 226 in the piston and fluid passageway 428 in the plug 420 are configured to provide a predetermined lubrication to the shoe face 422.
• the fluid passageway 428 comprises an enlarged opening 430 arranged to permit lubrication of the piston sphere 240.
• the enlarged opening 430 also continues to permit fluid communication between the fluid passageway 428 of the plug 420 and the fluid passageway 226 of the piston 200 in the event that the piston 200 and shoe 400 are angled or rotate with respect to one another.
• the fluid passageway 226 in the piston 200 and the fluid passageway 428 in the plug 420 are configured to provide force balancing for the piston 200.
• pressurised fluid in the barrel 60 of the hydraulic pump is permitted, via the fluid passageway 226 and fluid passageway 428, to a region between the plug 420 and the piston head 240.
• the surface area of the piston shaft 220 and the piston sleeve 260 towards the barrel 60 is greater than the surface area of the piston head 240 that faces in the opposing direction, towards the plug 420.
• the piston 220 and sleeve 260 provide a larger area (e.g.
• the piston 220 and sleeve 260 have a larger diameter than the piston head 240.
• the piston 220, sleeve 260, piston head 240, and fluid passageway 226 are configured so that pressurised fluid within the bore 62 primarily acts to presses the piston against the plug 420.
• the net force produced by the pressure therefore acts in the direction towards the angle block 120, which advantageously presses the plug 420 against the angle block 120, as well as reducing forces on the shoe 410.
• a dynamic transient net force acting to force the piston 200 away from the angle block 120 and shoe 400 may occur. This is because the pressure in the barrel 60 will change from relatively high pressure during the discharge stroke to relatively low pressure in the suction stroke and, as a result of the narrow fluid passageways limiting the fluid flow, the pressure may, momentarily, be higher at the piston head 420 before the pressure normalises due to the fluid passageways 226.
• Embodiments of the present invention mitigate against the wear and damage caused by the transient force acting to pull the piston 200 from the plug 400 as a crimping limp is not required.
• the plug 400 can be formed of stronger, more durable, wear resistant materials to resist the transient force.
• the piston and shoe assembly 110 comprises a piston sleeve 260.
• the piston sleeve 260 is installed along the piston shaft 220.
• the piston sleeve 260 has a diameter, ⁇ 4 , that is greater than the diameter, ⁇ 3 , of the piston sphere 240.
• the piston sleeve 260 effectively extends the working diameter of the piston 200 and the piston sleeve 260 diameter, ⁇ 4 , is sized for close fitting relationship with bore 62 of barrel 60.
• the diameter ⁇ 4 of piston sleeve 260 is greater than the diameter of the piston sphere ⁇ 3 to ensure the tackling of the piston against the plug during the discharge phase.
• the piston and shoe assembly 110 comprises a stop pin 280 that is inserted through corresponding openings in the piston sleeve 260 and the piston shaft 220 with a friction fit such that the piston sleeve 260 and piston shaft 220 are secured together.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Reciprocating Pumps (AREA)
• Details Of Reciprocating Pumps (AREA)

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Citations (3)

• 2024
  • 2024-05-10 EP EP24305724.7A patent/EP4647600A1/de active Pending
• 2025
  • 2025-03-13 CA CA3267617A patent/CA3267617A1/en active Pending
  • 2025-04-16 US US19/180,825 patent/US20250347276A1/en active Pending

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