A multi-stage valve having a valve housing containing an inlet port and an outlet port that communicate through means of an elongated chamber formed in the housing. An outer sealing unit is mounted in the chamber and is adapted to close in sealing contact against one of the ports. A control orifice is...http://www.google.fr/patents/US4672203?utm_source=gb-gplus-shareBrevet US4672203 - Two stage valve for use in pressure converter
