Two-stage hydraulic valves.

摘要

An electrically operated, two-stage hydraulic spool valve comprising a main stage (2) having a main spool (4), centring springs (9) acting on the main spool, a pilot stage (1) having a pilot spool (12) , and two solenoids (39) acting on respective ends of the pilot spool to control the operating position of the latter, the solenoids being opposed by return springs (18) also acting on respective ends of the pilot spool, the pilot stage comprising tank port means (23,24), supply port means (26), and two service ports (27,28), and the pilot spool comprising two portions (13,14), a spring (15) interposed between the two portions and operable to urge the two portions apart in a direction axially of the pilot spool so that on de-energisation of the solenoids, the portions of the pilot spool separate under the action of the spring to provide an interconnection between the pilot service ports and the tank port means. The tank port means comprise two tank ports (23,24) between which the two service ports (27,28) are disposed, and the supply port means (26) comprises two supply ports (26a,26b) disposed between the service ports (27,28) and spaced apart by an amount such that, in normal operation of the pilot valve, neither supply port sees the ends of the two portions of the pilot spool which are maintained in contact by the operation of the solenoids (39).