Patent ID: 7389795

Claim:
A valve assembly comprising a valve body, a first movable pressure responsive element, and a second moveable pressure responsive element, the valve body being provided with an inlet port, an outlet port and an exhaust port, the first pressure responsive element being moveable into engagement with a first valve seat to substantially block flow of fluid between the outlet port and the exhaust port, and the second pressure responsive element being movable into engagement with a second valve seat to substantially block flow of fluid between the inlet port and the outlet port, wherein the valve assembly further comprises a third movable pressure responsive element which may be moved to engage with the first pressure responsive element and move the first pressure responsive element out of engagement with the first valve seat so that flow of fluid between the outlet port and the exhaust port is permitted, wherein the first pressure responsive element is adapted to move in response to fluid pressure in a control chamber to engage with the first valve seat and the second pressure responsive element is adapted to move in response to fluid pressure at the inlet port to engage with the second valve seat, and wherein the valve assembly further comprises a switch valve having a first switch port connected to the inlet port of the valve assembly, a second switch port connected to the control chamber, a third switch port which vents to atmosphere, and a valve member which is movable between a first position in which the third switch port is blocked and flow of fluid from the first switch port to the second switch port is permitted, and a second position in which the first switch port is blocked and flow of fluid from the second switch port to the third port is permitted.