Patent ID: 7066310

Claim:
A piston cylinder unit comprising: a closed cylinder having an end wall; a piston rod guided through said end wall; a piston fixed to said piston rod for axial displacement in said cylinder, said piston dividing said cylinder into a working space surrounding the piston rod and a working space away from the piston rod; an annular seal between said piston and said cylinder; a volume equalizing space in said piston; a first valve which can be opened under pressure to admit fluid from said working space away from said piston rod to said volume equalizing space; a second valve which can be opened under pressure to admit fluid from said working space surrounding said piston rod to said volume equalizing space; at least one of said first and second valves comprising: a valve chamber in said piston and having a mouth opening into a respective one of said working spaces; a valve piston sealingly and displaceably mounted within said valve chamber and biased towards said mouth by a closing force; and a closing element coupled to said valve piston and extending between said valve piston and said mouth, said closing element being configured to close said mouth and displaceable with said valve piston from said mouth when pressure in said respective working space exceeds said closing force, wherein said at least one of said first and second valves is configured as a non-return valve providing flow communication between said respective working space and said volume equalizing space upon opening said mouth; a first non-return valve which can admit fluid from said volume equalizing space to said working space away from said piston rod; and a second non-return valve which can admit fluid from said volume equalizing space to said working space surrounding said piston rod.