A valve assembly includes a valve having a head and a stem. The head is configured to seal against a valve seat. The stem has a distal end. A first piston radially extends from the stem of the valve and is enclosed within a housing. A second piston is fixed to the distal end of the stem and seals against the housing. A first chamber 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 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 wherein during periods of insufficient gas pressure the spring device biases the valve to seal against the valve seat.