Hydraulic system having bypass valve effective to keep motor speed or pump output constant

Claim 1

A bypass valve for use in a hydraulic system having a hydraulic machine comprising a hydraulic motor or a pump connected to hydraulic supply and discharge lines, said bypass valve comprising means defining connections for connecting it shunting said machine and to said supply and discharge lines for controlling fluid therethrough in response to pressure drops across said machine, means comprising pressure-responsive means in said bypass valve responsive to pressure drops across said machine variably controlling flow through said valve and throttling fluid flow through said valve as the pressure drop across said machine increases and responsive to a predetermined small drop in pressure across said machine for allowing fluid flow through said valve approximately equal to fluid leakage in said machine, said means comprising said pressure-responsive means comprises means bypassing hydraulic fluid through said bypass valve such that the sum of the amount of fluid through said valve and the leakage fluid of said machine is substantially constant, said valve comprises means including said pressureresponsive means defining flow passages through said valve havinG different pressure-flow characteristics, said means including said pressure-responsive means constitute relatively movable means defining grooves of varying cross section constituting said flow passages, said relatively movable means comprise relatively rotatable means defining said grooves angularly disposed relative to each other, said grooves having different cross sections from each other, said relatively rotatable means are rotatable to positions for selecting which of said grooves will function as flow passages for a given relative position of said rotatable means.