Safety valve for fluid systems

In a fluid system having a fluid-operated device and a supply line for supplying pressurized fluid to said device at a predetermined line pressure, a safety valve interposed in said supply line, said safety valve comprising:

• a housing with supply, outlet, and exhaust ports in said housing., a movable poppet valve member carried by a valve stem for providing fluid communication between said supply and outlet ports when in an open position and for preventing said fluid communication when in a closed position, said line pressure tending to forcibly urge said poppet valve member to its closed position;
• a piston movable in a piston chamber in said housing and connected to said valve stem;
• first passage means in said housing leading from said supply port to said piston chamber;
• second passage means in said housing leading from said piston chamber to said outlet port;
• and restriction means for restricting fluid flow in said first passage means;
• the relative dimensions of said piston and said poppet valve member being such that said piston and said valve stem will shift said poppet valve member to its open position against the force of said line pressure when a predetermined proportion of said line pressure has been reached in said piston chamber;
• said safety valve also including an exhaust piston movable in an exhaust closure chamber within said housing;
• an exhaust valve member connected to said exhaust piston and movable therewith between an open position providing fluid communication between said outlet and exhaust ports and a closed position preventing fluid communication therebetween;
• third passage means in said housing leading from said supply port to said exhaust closure chamber so that said line pressure can forcibly act on said exhaust piston and tend to urge said exhaust valve member to its closed position;
• operator means selectively actuable between at least two positions respectively permitting and cutting off flow of said line pressure to said piston chamber and to said exhaust closure chamber;
• the relative dimensions of said exhaust piston and said exhaust valve member being such that said exhaust valve member will shift to its closed position when said line pressure is present in said exhaust closure chamber and such that said exhaust valve member will shift to its open position in order to exhaust said outlet port through said exhaust port when said line pressure is cut off from said exhaust closure chamber;
• said safety valve further including a one-way check valve in said second passage means for permitting flow therethrough only from said piston chamber to said outlet port;
• and said restriction means including a flow orifice in said first passage means, said flow orifice having a cross-sectional flow area smaller than at least a portion of said first passage means upstream of said orifice.