Servo-valve convertible construction

Claim 1

A control valve in combination with a hydraulic system which includes a variable displacement pump and a flow restrictor, an output line therebetween, a delivery line from the restrictor for connection to a load, a return line and a control displacement line to the pump, means responsive to output line pressure acting to reduce pump dislacement, the pump displacement being varied directly by pressure variations in said displacement control line acting on pressure responsive displacement control means; said valve including a valve body and a spool which is axially movable therein and defines therewith first and second restricted passages, said valve body having means for connection with said output, displacement controls, and return lines to provide a pilot flow of fluid from the output line and through said passages to the return line and to the displacement control of line for varying pump displacement by the pressure intermediate said passages, a spring biasing said spool in one direction and toward one end of the valve body to close said second passage to the return line to raise the pressure in the displacement control line whereby pump displacement is increased, and means for connecting said one end of the valve body with the output line whereby pump output pressure is effective to move the spool in the other direction and against said spring and to open said second passage to the return line to lower pressure in the displacement control line whereby pump displacement is decreased; said valve further including a spool abutment device comprising a cylinder, a piston movable therein, a spring biasing said piston in one direction and toward one end of the cylinder, an axially movable pin extending from the piston and through the other end of the cylinder, means removably connecting said other end of the cylinder to said one end of the valve body whereby the pin is engageable by abutting the spool and only limits movement of the spool in said one direction only, and means for connecting said one end of the cylinder with the output line and the other end of the cylinder with the delivery line such that the pressure differential effected by the restrictor and operating against said piston and last named spring positions said pin in accordance with said pressure differential and allows pump displacement to be varied only up to a selected maximum pump output and without otherwise interfering with the operation of the control valve.