This diaphragm is the flexible membrane inside the Comet pump that separates the pumping chamber from the drive mechanism. It flexes in response to the pump’s reciprocating motion, drawing fluid 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 leakage from the pump housing. The original manufacturer’s diaphragm is molded to the same thickness and durometer as the pump’s original seal face, which maintains the correct stroke volume without requiring shimming or adjustment. On replacement, inspect the pump head and valve seats for debris, and ensure the diaphragm is centered before tightening the retaining bolts.