Relief valve head for piston-style flush valve

A flush valve including a body having an inlet and an outlet, a valve seat at said outlet, a piston assembly movable in said body toward and away from said valve seat to control flow from said inlet through said outlet, a pressure chamber in said body above said piston assembly and normally maintaining said piston assembly closed upon said valve seat, said piston assembly including a refill orifice connecting said chamber with said body inlet,

• said piston assembly having a vent passage connecting said pressure chamber with said outlet, a relief valve in said piston assembly controlling flow through said vent passage, means for opening said relief valve to vent said chamber, causing said piston assembly to move away from said valve seat to open flow through said outlet,
• a seal extending about said vent passage, spring means urging said relief valve toward said seal to close said vent passage,
• said relief valve including an outwardly directed shoulder positioned to close on said vent passage seal, and a plurality of peripherally disposed indented flow openings in said shoulder to accommodate flow from said pressure chamber through said vent passage.