Variable back pressure valve

Claim 1

In a back pressure valve comprising a valve body including port means enabling fluid flow into the body, an exhaust orifice in said valve body, a diaphragm normally closing the exhaust orifice and being lifted from the exhaust orifice for discharging fluid therethrough, that improvement comprising a rod extending into the valve body and longitudinally movable with respect thereto with the inner end of the rod being operatively associated with the diaphragm and the outer end of the rod being operatively associated with an external control actuator to alter the opening and closing characteristics of the diaphragm, said diaphragm is held closed against fluid pressure in the body by a main coil spring, said rod including a ring mounted thereon for engagement with the end of the main spring remote from the diaphragm for varying the pressure exerted on the diaphragm by the spring, said valve includes a weak coil spring encircling the push rod and main coil spring engaged by the push rod with the inner end of the weak spring engaging the diaphragm to close the diaphragm in the event fluid flow ceases and pressure is removed from the diaphragm and main spring engaged with the rod by movement of the push rod outwardly thereby preventing entry of air through the exhaust orifice, the inner end of the rod extending into the main spring for maintaining the main spring and push rod in aligned relation.