A valve includes a body, a plug and a diaphragm defining an aperture and a seat. The diaphragm is substantially movable in response to a force applied to the seat by the plug. The valve can be cycled between an open state in which the plug is free of the seat, a closed state in which the plug is seated against the seat, and a third state in which the plug is seated against the seat and substantially deflects the diaphragm.