Liquid pump using elastomeric piston, piston assembly and manufacturing method thereof

Abstract

The invention provides a liquid pump using an elastomeric piston. The liquid pump has a piston assembly ( 10 ), which comprises: a piston rod ( 11 ); a piston head ( 12 ); a piston engaging portion ( 15 ) which is between the piston rod and the piston head in a necking shape; and a piston ( 13 ) made of an elastomeric material and sleeved around the piston engaging portion between the piston rod and piston head. The piston rod and piston head are formed separately and then assembled together. The piston engaging portion ( 15 ) is composed of a piston-engaging-portion formation part of at least one of the piston rod and the piston head. The invention also provides a method of manufacturing the piston assembly ( 10 ). The invention further provides a piston assembly ( 10 ) for a liquid pump. The piston assembly has a piston ( 13 ) which is provided with an annular notch ( 133 ) formed on the periphery of an upper end of the piston ( 13 ) where an annular inner flange ( 131 ) is formed. The piston assembly and its manufacture method are helpful to improving product precision and quality and facilitate automated assembly, and are specially used for the liquid pumps using an elastomeric piston.

1 . A liquid pump using an elastomeric piston, for mounting on a liquid container to pump liquid in said container out of said container, said liquid pump comprising a piston assembly which is disposed in a cylinder slidably in a longitudinal direction of the pump, said cylinder defining a liquid reservoir for accommodating liquid therein, said piston assembly comprising:
 a piston rod, formed with a fluid passage in a center of the piston rod in the longitudinal direction;   a piston head, connected to a lower end of said piston rod;   a piston engaging portion in the form of a neck between said piston rod and said piston head, said piston head being connected with said piston rod via said piston engaging portion, said piston engaging portion being formed with a transverse passage that diametrically extending through said piston engaging portion and is in fluid communication with said fluid passage so as to provide a passage for the liquid accommodated in said liquid reservoir to be pumped out of said container; and   a piston made of an elastomeric material, fitted over said piston engaging portion between said piston rod and said piston head for releasably closing said transverse passage,   said piston assembly being configured such that: when said piston assembly is stationary with respect to said cylinder, said piston remains in its engaging position with said piston engaging portion so as to close said transverse passage and block the fluid communication of said liquid reservoir with the outside of said container through said fluid passage; as said piston assembly is moved downwards relative to said cylinder, said piston deforms to offset from said engaging position so as to open said transverse passage in said piston engaging portion and allow said liquid reservoir to be communicate with the outside of said container through said fluid passage; as said piston assembly is moved upwards relative to said cylinder, said piston remains in said engaging position so as to close said transverse passage and block the fluid communication of said liquid reservoir with the outside of said container through said fluid passage,   wherein said piston rod and said piston head are formed separately and then assembled together, said piston engaging portion being composed of a piston-engaging-portion formation part of at least one of said piston rod and said piston head.   
     
     
         2 . The liquid pump of  claim 1 , wherein said piston head comprises a base and a guide stub extending upwards form said base, said piston rod being formed with a guide stub receiving hole at its lower end, said guide stub receiving hole being formed as part of said fluid passage, said guide stub portion being inserted into and fitted to said guide stub receiving hole so as to assemble said piston head onto said piston rod,
 said guide stub being formed with at least one longitudinal slot along a longitudinal length of said guide stub, said longitudinal slot constituting a longitudinal passage in said guide stub receiving hole, said piston engaging portion being formed with said transverse passage corresponding to said longitudinal slot in number, with said longitudinal slot correspondingly communicating with said transverse passage in said piston engaging portion, thereby providing a passage from said transverse passage to said fluid passage.   
     
     
         3 . The liquid pump of  claim 2 , wherein said piston engaging portion is provided by both of said piston rod and said piston head, wherein said piston rod, at its lower end, is formed with a cylindrical reduced diameter tube portion which serves as one of said piston-engaging-portion formation parts, said reduced diameter tube portion defining part of said guide stub receiving hole, and
 said piston head, at an upper end of its base, is formed with a cylindrical reduced diameter boss which serves as the other of said piston-engaging-portion formation parts, said reduced diameter tube portion and said reduced diameter boss having the same diameter, whereby said reduced diameter tube portion and said reduced diameter boss abut against each other to cooperatively constitute said piston engaging portion when said piston head is assembled to said piston rod.   
     
     
         4 . The liquid pump of  claim 3 , wherein said transverse passage of said piston engaging portion is formed in said reduced diameter boss. 
     
     
         5 . The liquid pump of  claim 4 , wherein said transverse passage of said piston engaging portion is formed integrally with said longitudinal slot of said guide stub. 
     
     
         6 . The liquid pump of  claim 3 , wherein said transverse passage of said piston engaging portion is formed in said reduced diameter tube portion. 
     
     
         7 . The liquid pump of  claim 3 , wherein said transverse passage of said piston engaging portion is formed in both said reduced diameter tube portion and said reduced diameter boss. 
     
     
         8 . The liquid pump of  claim 2 , wherein said piston engaging portion is provided only by said piston head, wherein said piston head, at an upper end of its base, is formed with a cylindrical reduced diameter boss which serves as said piston-engaging-portion formation part, when said piston head is assembled to said piston rod, said reduced diameter boss abutting against a lower end of said piston rod to cooperatively constitute said piston engaging portion. 
     
     
         9 . The liquid pump of  claim 2 , wherein said piston engaging portion is provided only by said piston rod, wherein said piston rod, at its lower end, is formed with a cylindrical reduced diameter tube portion which serves as said piston-engaging-portion formation part, said reduced diameter tube portion defining part of said guide stub receiving hole, when said piston head is assembled to said piston rod, said reduced diameter tube portion abutting against an upper end of said base of said piston head to constitute said piston engaging portion. 
     
     
         10 . The liquid pump of  claim 2 , wherein said guide stub is formed with a recess or protrusion along its periphery, and a mating protrusion or recess is formed an inner circumferential surface of said guide stub receiving hole, assisting to assemble said piston head to said piston rod. 
     
     
         11 . The liquid pump of  claim 1 , wherein said piston comprises a substantially cylindrical body with opposite open ends, said body being formed with an annular inner flange radially protruding inwardly for fitting around a periphery of said piston engaging portion so as to releasably close said transverse passage, and being formed with a sealing lip slidably abutting against a sidewall of said cylinder. 
     
     
         12 . The liquid pump of  claim 11 , wherein said annular inner flange is formed at an upper end of said body, and said sealing lip is an end edge of a lower portion of said body which is gradually flared and thinned as said lower portion extends downwards. 
     
     
         13 . The liquid pump of  claim 12 , wherein an annular notch is formed, at said upper end of said body where said annular inner flange is formed, along a peripheral edge of said body. 
     
     
         14 . The liquid pump of  claim 13 , wherein said liquid pump further comprises an integrated threaded sleeve-cylinder cap and a press head, said cylinder being connected with said integrated threaded sleeve-cylinder cap on a lower side thereof, said press head being connected to an upper end of said piston rod, said press head having an upper stop position and a lower stop position of its press stroke with respect to said integrated threaded sleeve-cylinder cap,
 said integrated threaded sleeve-cylinder cap including an inner sleeve and an outer sleeve which extend in the longitudinal direction, said outer sleeve for engaging an open neck of said container so as to mount said liquid pump on said container, said inner sleeve for engaging an upper end of said cylinder so as to connect said cylinder to said integrated threaded sleeve-cylinder cap on the lower side thereof and thus to form a closed cylinder, when said press head is at the upper stop position of said press stroke with respect to said integrated threaded sleeve-cylinder cap, a lower end of said inner sleeve being engaged in said annular notch of said piston.   
     
     
         15 . The liquid pump of  claim 14 , wherein said cylinder is formed in its sidewall with a balancing vent for balancing pressures within and outside said container, when said press head is at the upper stop position of said press stroke with respect to said integrated threaded sleeve-cylinder cap, said balancing vent being above an abutment point of said sealing lip of said piston with the sidewall of said cylinder, and below the abutment point of said inner sleeve of said integrated threaded sleeve-cylinder cap with said piston. 
     
     
         16 . The liquid pump of  claim 1 , wherein said piston rod, at its joint with said piston engaging portion, has a conical step surface tapering towards said piston engaging portion, and said piston head, at its joint with said piston engaging portion, has a steep step surface which is substantially perpendicular to the longitudinal direction, said conical step surface providing a space for said piston to deform. 
     
     
         17 . The liquid pump of  claim 16 , wherein said piston engaging portion, at its joint with said conical step surface, has an increased diameter portion. 
     
     
         18 . A method of manufacturing said piston assembly of said liquid pump of  claim 1 , said method comprising:
 separately molding and providing said piston rod, said piston head and said piston;   fitting said piston over one of said piston rod and said piston head that is suitable for receiving said piston;   assembling said piston rod and said piston head together, with said piston being fitted around said piston engaging portion between said piston rod and said piston head.   
     
     
         19 . A piston assembly for use in a liquid pump for mounting to a liquid container to pump liquid in said container out of said container, said liquid pump comprising a piston assembly which is disposed in a cylinder slidably in a longitudinal direction of the pump, said cylinder defining a liquid reservoir for accommodating liquid therein, said piston assembly comprising:
 a piston rod, formed with a fluid passage in a center of the piston rod;   a piston head, connected to a lower end of said piston rod;   a piston engaging portion in the form of a neck between said piston rod and said piston head, said piston head being connected with said piston rod via said piston engaging portion, said piston engaging portion being formed with a transverse passage that diametrically extending through said piston engaging portion and is in fluid communication with said fluid passage so as to provide a passage for the liquid accommodated in said liquid reservoir to be pumped out of said container; and   a piston made of an elastomeric material, fitted over said piston engaging portion between said piston rod and said piston head for releasably closing said transverse passage,   said piston assembly being configured such that: when said piston assembly is stationary with respect to said cylinder, said piston remains in its engaging position with said piston engaging portion so as to close said transverse passage and block the fluid communication of said liquid reservoir with the outside of said container through said fluid passage; as said piston assembly is moved downwards relative to said cylinder, said piston deforms to offset from said engaging position so as to open said transverse passage in said piston engaging portion and allow said liquid reservoir to be communicate with the outside of said container through said fluid passage; as said piston assembly is moved upwards relative to said cylinder, said piston remains in said engaging position so as to close said transverse passage and block the fluid communication of said liquid reservoir with the outside of said container through said fluid passage,   wherein said piston comprises a substantially cylindrical body with opposite open ends, said body, at its upper end, being formed with an annular inner flange radially protruding inwardly for fitting around a periphery of said piston engaging portion so as to releasably close said transverse passage, and, at its lower end, being formed with a sealing lip slidably abutting against a sidewall of said cylinder, said sealing lip being an end edge of a lower portion of said body which is gradually flared and thinned as said lower portion extends downwards, said body, at its upper end where said annular inner flange is formed, being formed with an annular notch along a peripheral edge of said body.   
     
     
         20 . The piston assembly for use in a liquid pump of  claim 19 , wherein a longitudinal thickness of said annular inner flange is greater than a radial thickness of said body of said piston.