Hydraulic element and displacement pump having such an element

Abstract

The present invention concerns a hydraulic element comprising a sleeve-shaped casing and a piston reciprocable in a longitudinal direction in the sleeve-shaped casing. To provide a hydraulic element for use in displacement pumps for conveying small amounts of liquid, in which the danger of breakage or deflection of the hydraulic element is reduced, it is proposed according to the invention that the piston has a cavity extending in the longitudinal direction and having a cavity entry, wherein there is provided a pin which extends through the cavity entry into the cavity and which is connected to the sleeve-shaped casing at the sleeve-shaped casing or by way of an intermediate element so that in a reciprocating movement of the piston a relative movement occurs between the piston and the pin. The present invention further concerns a displacement pump having the hydraulic element according to the invention.

1 . A hydraulic element ( 10 ) comprising a sleeve-shaped casing ( 11 ) and a piston reciprocable in a longitudinal direction ( 40 ) in the sleeve-shaped casing ( 11 ),
 characterised in that the piston ( 12 ) has a cavity ( 13 ) extending in the longitudinal direction ( 40 ) and having a cavity entry ( 14 ), wherein there is provided a pin ( 15 ) which extends through the cavity entry ( 14 ) into the cavity ( 13 ) and which is connected to the sleeve-shaped casing ( 11 ) at the sleeve-shaped casing ( 11 ) or by way of an intermediate element so that in a reciprocating movement of the piston ( 12 ) a relative movement occurs between the piston ( 12 ) and the pin ( 15 ).   
     
     
         2 . A hydraulic element ( 10 ) according to  claim 1  characterised in that the piston ( 12 ) is cylindrical and the sleeve-shaped casing ( 11 ) is hollow-cylindrical, wherein the outside diameter of the piston ( 12 ) substantially corresponds to the inside diameter of the sleeve-shaped casing ( 11 ). 
     
     
         3 . A hydraulic element ( 10 ) according to  claim 1  characterised in that the cavity ( 13 ) in the longitudinal direction ( 40 ) and/or the pin ( 15 ) is of a circular cross-section. 
     
     
         4 . A hydraulic element ( 10 ) according to  claim 1  characterised in that the cavity ( 13 ) is of a constant cross-section in the longitudinal direction ( 40 ) and the pin ( 15 ) in a cross-section substantially completely fills the cavity ( 13 ) so that the effective piston surface ( 18 ) is substantially formed by the cross-sectional area of the piston ( 12 ) less the cross-sectional area ( 19 ) of the cavity ( 13 ). 
     
     
         5 . A displacement pump ( 1 ) for conveying a liquid comprising a delivery chamber ( 20 ), a displacement element ( 21 ), wherein the displacement element ( 21 ) is reciprocable between a pressure position and a suction position, wherein a volume of the delivery chamber ( 20 ) is smaller in the pressure position of the displacement element ( 21 ) than a volume of the delivery chamber ( 20 ) in the suction position of the displacement element ( 21 ), a hydraulic chamber ( 16 ), wherein the displacement element ( 21 ) separates the delivery chamber ( 20 ) from the hydraulic chamber ( 16 ), a hydraulic element ( 10 ), wherein the hydraulic element ( 10 ) is connected to the hydraulic chamber ( 16 ), wherein the hydraulic element ( 10 ) for applying a force to the displacement element ( 21 ) has a hydraulic liquid arranged in the hydraulic chamber ( 16 ), wherein a part of the hydraulic element ( 10 ) is reciprocable between a first and a second hydraulic position, and a drive for driving the hydraulic element ( 10 ), characterised in that the hydraulic element ( 10 ) is a hydraulic element ( 10 ) according to  claim 1 . 
     
     
         6 . A displacement pump ( 1 ) according to  claim 5  characterised in that the ratio of the cross-sectional area of the piston ( 12 ) to the cross-sectional area ( 19 ) of a portion of the pin ( 15 ), in which the pin ( 15 ) extends into the cavity ( 13 ), is not more than 3. 
     
     
         7 . A displacement pump ( 1 ) according to  claim 5  characterised in that the piston ( 12 ) is subjected to the action of hydraulic liquid only on the side towards the pin ( 15 ), wherein the connecting rod is connected to the piston ( 12 ) and the crankshaft in such a way that a rotary movement of the crankshaft is converted into an oscillating linear movement of the piston ( 12 ) by the connecting rod. 
     
     
         8 . A displacement pump ( 1 ) according to  claim 5  characterised in that at its end remote from the cavity entry ( 14 ) the cavity ( 13 ) has a cavity outlet, through which a fluid can leave the cavity, wherein a fluid can flow into the cavity from the reservoir through the cavity outlet. 
     
     
         9 . A displacement pump ( 1 ′) for conveying a liquid comprising a delivery chamber ( 20 ), a displacement element ( 10 ), wherein a part of the displacement element ( 10 ) is reciprocable between a pressure position and a suction position, wherein a volume of the delivery chamber ( 20 ) is smaller in the pressure position of the displacement element ( 10 ) than a volume of the delivery chamber ( 20 ) in the suction position of the displacement element ( 10 ), characterised in that the displacement element ( 10 ) is a hydraulic element ( 10 ) according to  claim 1 , wherein the pin ( 15 ) is arranged in the delivery chamber ( 20 ). 
     
     
         10 . A displacement pump ( 1 ) for conveying a liquid according to  claim 5  wherein the displacement element ( 21 ) is in the form of a diaphragm. 
     
     
         11 . A displacement pump ( 1 ) according to  claim 5  wherein the ratio of the cross-sectional area of the piston ( 12 ) to the cross-sectional area ( 19 ) of a portion of the pin ( 15 ), in which the pin ( 15 ) extends into the cavity ( 13 ), is not more than 2. 
     
     
         12 . A displacement pump ( 1 ) according to  claim 7  wherein the drive has a crankshaft and a connecting rod. 
     
     
         13 . A displacement pump ( 1 ) according to  claim 8  wherein the cavity outlet is connected to a reservoir.