This diaphragm is the flexible membrane inside the sprayer's pump that separates the fluid chamber from the drive mechanism. It flexes with each pump stroke, drawing liquid into the chamber on the intake stroke and forcing it out under pressure on the discharge stroke. A ruptured or stretched diaphragm causes a loss of prime, reduced output pressure, or fluid leaking into the pump crankcase. This original part is molded to the same thickness and durometer as the factory-installed diaphragm, which is necessary for the pump to maintain its rated displacement without excessive flex fatigue. When replacing, ensure the diaphragm is centered in the housing and that the retaining bolts are torqued to specification to prevent pinching.