This diaphragm is the flexible pumping element inside the sprayer’s positive-displacement pump. It separates the fluid chamber from the drive mechanism, converting the reciprocating motion of the piston into a pressure pulse that moves liquid through the spray circuit. A ruptured or fatigued diaphragm causes pressure loss, uneven spray patterns, and fluid leakage into the crankcase. The manufacturer machines the diaphragm to the same thickness and contour as the original assembly so that the pump’s stroke volume and cracking pressure remain within specification. On replacement, inspect the piston face and valve seats for scoring before reassembly.