In a safety valve for use in a vacuum system to isolate an auxiliary circuit from a vacuum generator should a leak occur in the auxiliary circuit, said safety valve comprising:
- a housing having a chamber and a blind bore, said blind bore having a first end and a second end therein, said chamber having an inlet port connected to said auxiliary circuit and an outlet port connected to said vacuum generator, said housing having a valve seat located between the inlet and outlet ports;
- a flow-responsive movable member located between said inlet and outlet ports;
- a first valve member connected to said movable member upstream said valve seat;
- a stop member located in said chamber;
- resilient means for biasing said movable member toward a first rest position against stop member in which said first valve member is away from said valve seat;
- a piston located in said blind bore, said piston being connected to said movable member;
- a first conduit for connecting the first end of said blind bore to a reservoir;
- a second conduit for connecting the second end of said blind bore to the reservoir, said reservoir, first and second conduits and blind bore forming a closed circuit which allows fluid to flow between the reservoir and said blind bore, said movable member responding to a predetermined rate of air flow from the auxiliary circuit through the chamber by overcoming said resilient means to move said first valve member from said first rest position toward said valve seat and said piston from a second rest position past said second conduit and toward said first conduit, said piston movement communicating fluid from said blind bore to said reservoir through said first conduit;
- first and second seals located in said blind bore and engaging said piston to separate said chamber and blind bore;
- a drain port located between said first and second seals to provide a flow path to the surrounding environment for any fluid that may seep past said first seal from said blind bore and thereby avoid fluid contamination of said chamber by said fluid;
- a restriction member located in said first conduit for controlling the flow rate of fluid between said blind bore and reservoir, said restriction member being adjustable to control said flow rate and correspondingly the time required to move said valve into engagement with said valve seat to interrupt communication of air to said vacuum generator;
- and
- a second valve member located in said second conduit to prevent fluid flow from said blind bore toward said reservoir while allowing free flow of fluid from said reservoir to said blind bore of movement of the piston toward said second rest position to assure that the bore is full of fluid at all times.