Load check and pressure compensating valve

A load check and pressure compensating valve of the type disposed in series flow relationship between a metering orifice and a service passage connected to a hydraulic motor comprising:

• a body having a bore therein;
• a valve element slidably disposed in the bore and being movable between a load check position and an infinitely variable operating position;
• means defining a pressure control flow path from the metering orifice to the service passage when the valve element is at the operating position, the flow path including a pressure control orifice with the size of the control orifice being determined by the extent to which the valve element is moved from the load check position, the valve element being moved to the operating position by fluid passing through the metering orifice;
• a load piston normally biasing the valve element to the load check position;
• a first variable volume chamber between the valve element and the load piston;
• a second variable volume chamber formed between the load piston and the body;
• a spring disposed in the second chamber biasing the load piston toward the valve element and hence biasing the valve element to the load check position;
• means for communicating load pressure from the service passage into the first chamber.

A hydraulic system having a plurality of hydraulic motors and a load sensing hydraulic pump having a displacement controller comprising:

• a load pressure signal network operatively connected to the motors and having a control pressure line which receives the highest load pressure occurring at the motors, the control pressure line being connected to the displacement controller;
• means for limiting the pressure of the fluid in the control pressure line to a predetermined maximum level;
• a plurality of control valves each being connected to at least one of the motors, each of the control valves, including
• an inlet port connected to the pump;
• a pair of service passages connected to the associated hydraulic motor;
• a valve member movable in opposite directions from a neutral position to infinitely variable operating positions;
• a load check and pressure compensating valve element movable from a load check position to an infinitely variable operating position;
• means defining a flow control flow path from the inlet port to one of the service passages when the valve member and the valve element are at operating positions, the flow path including a metering orifice and a pressure control orifice disposed in series flow relationship downstream of the metering orifice with the size of the metering orifice being determined by the extent to which the valve member is moved from the neutral position and the size of the control orifice being determined by the extent to which the valve element is moved from the load check position, the valve element being moved to the operating position by fluid passing through the metering orifice;
• a load piston normally biasing the valve element to the load check position;
• a first variable volume chamber between the valve element and the load piston;
• a second variable volume chamber defined in part by the load piston and being connected to the control pressure line;
• a spring disposed in the second chamber biasing the load piston toward the valve element and hence biasing the valve element to the load check position;
• and
• means for communicating load pressure from the one service passage into the first chamber so that the valve element is held in the load check position when the load pressure in the one service passage is greater than the fluid passing through the metering orifice.