Dual crossover relief and case surge valve for hydraulic motors and pumps

Claim 1

In a hydraulic device including operating means in a hydraulic circuit having respective passages communicating with the operating means and each passage liable to overload pressure, and an overload bypass having means defining a port communicating at one end with one of said passages and communicating at its opposite end with the other of said passages, the improvement comprising: a valve having means normally biasing iT into closing relation to said port and the valve being movable in one direction only for opening the port; different hydraulic fluid thrust-receiving surfaces of said valve exposed respectively to hydraulic fluid pressure from said passages to effect movement of the valve in said one opening direction in opposition to said biasing means when either of said passages experiences pressure overload; said valve comprising a generally spool configuration carrying said surfaces intermediately along its length and at one end thereof opposite to the end toward which said biasing means thrusts; a longitudinal blind end bore in the spool valve opening through said end opposite to the end against which the biasing means thrusts; the blind end of said bore presenting a thrust surface comprising part of said surfaces; and a reciprocable plunger in said bore and longitudinally spaced hydraulic pressure ports in said valve respectively communicating with said bore between said blind end surface and said plunger and with said bore and a surface on said plunger facing in the same direction as said blind end surface and providing pressure responsive surface alternative to said blind end surface.