Valve assembly

摘要

Disclosed is a pneumatic-mechanical hybrid valve assembly comprising a valve 30 having a head 48 and a stem 50. The head is configured to seal against a valve seat 20. A first piston 34 radially extends from the stem of the valve and is enclosed within a housing 32. A second piston 36 is fixed to a distal end 54 of the stem and seals against the housing. A first chamber 74 is defined by the first piston, second piston and the housing and receives a compressed gas and maintains a desired gas pressure. A spring device 38 is disposed intermediate the first piston and the housing. During normal operation of the engine, the gas pressure within the first chamber seals the head of the valve against the valve seat with the spring device in a compressed arrangement and during periods of insufficient gas pressure the spring device biases the valve to seal against the valve seat. The spring mechanism thus provides a failsafe biasing means to urge the valve closed in the event of a insufficient gas pressure. An engine having such a valve assembly and a method of opening a valve are also disclosed.