Patent ID: 7175154

Claim:
Piston structure for two-directional axial motion in a piston cylinder containing liquid or gaseous fluid, said piston structure has a first side facing a first chamber (K 1 ) and a second side facing a second chamber (K 2 ), a piston shaft ( 4 ) is attached to said first or second side of said piston ( 1 ), and in a recess formed in an outer portion of said piston ( 1 ) an O-ring ( 5 ) made of a resilient material and having a given cross-sectional diameter is placed which seals the wall of said piston cylinder ( 2 ), the axial width and at least in some places the radial depth of said recess ( 6 ) formed in the outer portion of said piston ( 1 ) are greater than the cross-sectional diameter of said O-ring ( 5 ), the O-ring ( 5 ) is placed in said recess ( 6 ) so that it is able to move owing to the pressure difference existing between the first side and the second side, between a first position facing the first side and a second position facing the second side, characterized in that, the outer portion of the piston and the wall of the piston cylinder define a first space adjacent the first side of the piston and a second space adjacent the second side of the piston such that the first space forms a first conduit having a first cross-sectional area for fluid flow between the first side of the piston and the recess and the second space forms a second conduit having a second cross-sectional area for fluid flow between the second side of the piston and the recess, and when said O-ring ( 5 ) is in its first position the cumulated cross-sectional area of a flow path between said recess ( 6 ) and the first side of said piston ( 1 ) is A 1 , and the cross-sectional area of a flow path between said recess ( 6 ) and the second side of said piston ( 1 ) is the second cross-sectional area of the second conduit, and when said O-ring ( 5 ) is in its second position the cumulated cross-sectional area of said flow path between said recess ( 6 ) and the second side of said piston ( 1 ) is A 2 , and the cross-sectional area of said flow path between said recess ( 6 ) and the first side of said piston ( 1 ) is the first cross-sectional area of the first conduit, where the smaller of A 1 and A 2 is smaller than the first cross-sectional area by orders of magnitude and smaller than the second cross-sectional area by orders of magnitude, and in the first and second position the direction of the possible liquid flow between first and second chambers (K 1 ,K 2 ) is opposite.