Pilot valves for two-stage hydraulic devices

A solenoid-operated, proportional control pilot valve for a two-stage hydraulic device comprises a housing, a bore formed in the housing, an inlet port, at least one service outlet port and two tank outlet ports also formed in the housing and communicating with said bore, a spool slidably mounted in said bore for movement in opposite directions from a normal null position in order to control fluid flow from the inlet port to a selected outlet port so as to deliver fluid under pressure to the second stage of the device to actuate the latter in one direction or an opposite direction from a normal null position, the spool being formed with two passageways each extending interanlly of the spool between one end face of the latter and different points on the periphery of the spool, and the pilot valve further comprising two spool control devices, at least one of which is a solenoid, associated with respective ends of the spool, said solenoid being operated form a source of electrical control signals, the magnitide of which is proportional to the movement of the pilot valve spool and hence to the flow of fluid from the pilot valve, said control devices in normal operation seating against the end faces of the spool, when electric input is applied to the solenoid, to close the passageways against fluid flow therethrough, and becoming unseated when electrical input is interrupted to the solenoid whereby both ends of the second stage are at a common pressure so as quickly to relieve the pressure in the second stage of the device, thereby permitting fast return of the latter to the null position.