Abstract: A fluid flow control valve meters, in response to a fluid control signal, fluid flow received at a supply pressure and released at an output pressure utilizing a folded elastomeric diaphragm as the fluid flow metering member. The diaphragm regulates fluid flow through a passageway in a piston disposed in a valve body, which passageway provides for fluid communication between a fluid supply port and a fluid output port. The piston is displaced as a function of control signal fluid pressure, which in turn produces a change in the relationship between the folded-over portion of the diaphragm and an outlet duct of the piston passageway.