Patent ID: 8517049

Claim:
A progressive hydraulic pressure relief valve (V, V′) for controlling pressure peaks in hydraulic motors and hydraulic circuits, which is mounted within a body ( 1 , 1 b ) of a hydraulic block for communication with a supply line (P, P′) and a discharge line (T, T′), said pressure relief valve (V, V′) comprising: a cartridge ( 6 ), said cartridge including internal chambers or internal chambers including a main spring chamber (C 1 ) defined by an inner surface of the cartridge, said cartridge ( 6 ) having a ring of radial through holes ( 6 a ) and one or more holes ( 6 b ) for communication of the main spring chamber (C 1 ) with the discharge line (T); a spring-holding plug ( 3 ) at an upper end of the cartridge ( 10 ); a closure member ( 10 ) having an outer surface and an axial through hole ( 10 a ), the outer surface of the closure member further defining the main spring chamber (C 1 ), said closure member ( 10 ) being composed of a head ( 10 b ), a cylindrical surface ( 10 c ) and an end part ( 10 d ); a main spring ( 8 ) inside the cartridge; a piston ( 5 ) inside the cartridge, the piston ( 5 ) having a bottom surface and an axial through hole ( 5 a ), the bottom surface of the piston further defining the main spring chamber (C 1 ); a setting spring ( 12 ) inside the cartridge and the spring holding plug ( 3 ); a spring plate ( 4 ) in the spring holding plug ( 3 ) at an end of the setting spring ( 12 ); a plate ( 11 ) with an axial through hole ( 11 a ) at an opposite end of the setting spring; and a chamber (C 2 ) defined by the piston ( 5 ) and the spring-holding plug ( 3 ); said cartridge ( 6 ) having a ring of radial through holes ( 6 a ) and one or more holes ( 6 b ) for communication of the main spring chamber (C 1 ) with the discharge line (T); wherein said pressure relief valve (V) has coupling surfaces between: the head ( 10 b ) of the closure member ( 10 ) and an edge (S 1 ) of the cartridge ( 6 ), the surface ( 10 c ) of the closure member ( 10 ) and the interior of the cartridge ( 6 ), the end part ( 10 d ) of the closure member ( 10 ) and the hole ( 5 a ) of the piston ( 5 ), and the outer surface of the piston ( 5 ) and the interior of the cartridge ( 6 ) which are formed with geometric precision and sized to limit fluid leakage to less than 5 ml/min, at an operating pressure of the valve, said coupling surfaces being coaxial to ensure that friction during relative motion of the parts is negligible.