Air-oil amplifier

Claim 1

In a hydraulic system, the combination of: a hydraulic motor, a variably positionable control valve having a fluid actuating chamber and adapted to control flow to said hydraulic motor in relation to the pressure developed in said chamber; means providing a source of pilot air pressure at selectable pressures in a first range; means providing a source of oil; an amplifier means having a housing forming a bore therein, a valve spool slideable in said bore, said housing having an outlet port communicating with said actuating chamber of said control valve, first and second inlet ports respectively connected with said source of pilot air pressure and said source of oil, said spool forming first and second chambers in said bore at opposite ends of said valve spool, means including an axial passage in said spool continuously communicating said second chamber with said outlet port, said spool forming a first pressure responsive surface subject to the pressure at said outlet port communicated through said axial passage to urge said spool in one direction, said valve spool forming a second presssure responsive surface in said first chamber, said second pressure responsive surface being larger than said first pressure responsive surface, said first chamber being in communication with said source of pilot air pressure at selectable pressures for urging said spool in a direction to communicate said inlet port to said actuating chamber to supply oil from said source of oil to said actuating chamber at a pressure in a second range, the pressures in said second range being substantially higher than the pressure in said first range and in direct proportion to the latter for all positions of said spool.