SENTINEL diaphragm back pressure valves apply positive discharge pressure to a metering pump system to prevent siphoning and eliminate varying dosage rates caused by fluctuating downstream pressure.  The diaphragm is held against the valve seat by an internal spring.  When the preset pressure is exceeded, the diaphragm is forced up and system fluid flows through the valve to the injection point. The valves are preset for 50 psi, however they are field adjustable from 10 - 150 psi via the adjustment screw.  Installation should be as close to the injection point as possible to prevent system line drainage, and it is most important that all pumping system equipment such as pulsation dampeners and pressure gauges are between the pump and back pressure valve.