The Y-Check valve Type 304 is a weighted angle check valve and is used to automatically stop flow in the back direction when the fluid in the line reverses.  The valve closes by the dead weight of the weighted seat and functions when mounted in either the horizontal or vertical plane.  Y-Check valve Type 304 is superior to spring-loaded checks for corrosive service since they are not temperature sensitive.  Y-Check valves generally have lighter shut-off characteristics than ball checks at the same pressures.  The valve requires 2.9 PSI differential pressure for tight seal and 0.29 PSI process pressure to fully open.