A unitary diaphragm assembly for use primarily in conventional flush valves. The diaphragm assembly has a flexible diaphragm which includes a sealing portion and a mounting portion at the outer peripheral edge. A flow ring is positioned adjacent the sealing portion of the diaphragm. An elongated barrel member extends from the diaphragm in a longitudinal direction and includes a plurality of radial guides positioned circumferentially around the outer surface of the barrel member along a portion of the length of the barrel member. The diaphragm defines an orifice having a ring portion that flexes when a pressure difference is applied across the orifice thereby increasing the flow rate across the diaphragm. The orifice has a smaller diameter at a first end relative to a second end of the orifice. A method of compensating for a pressure difference across the diaphragm is also disclosed.