Hydraulic lowering check valve

Claim 1

A hydraulic brake check valve comprising: a housing having an inlet for connection with a consumer and an outlet, first piston means having a substantially constant diameter throughout the length thereof and being arranged in said housing and movable to a closing position in which said first piston means blocks connection between said inlet and said outlet, spring means urging said first piston means into said closing position, a passage connecting said inlet with one side of said piston to urge said piston into said closing position when said inlet is under fluid pressure, said passage extending axially of said first piston means and having a cross-section steadily decreasing in the direction opposite to said closing direction, non-return valve means in said first piston means and connected to said passage, second piston means in said housing and being provided with means for engaging said non-return valve means, the effective area of said non-return valve means being substantially less than that of said second piston means, said first piston means being provided with axially extending grooves, spaced around the periphery thereof, the cross-section of said grooves increasing in a direction towards said second piston means, said second piston means having means for engaging said first piston means, whereby said second piston means is adapted to open said non-return valve means against the fluid pressure prevailing in said passage to thereby provide a connection between said inlet and said outlet, and whereby the cross-section of the connection between said inlet and said outlet gradually increases upon movement of said first piston means from its closing position upon engagement by said second piston means.