An apparatus is disclosed that includes a fluid inlet in fluid communication with a valve assembly, the valve assembly structured to selectively permit the flow of a motive fluid from the fluid inlet to a fluid driven motor, and wherein the valve assembly further includes a first plunger and a second plunger, one of the first plunger and the second plunger including a plurality of axially incorporated fluid channels, wherein the plunger including a plurality of axially incorporated fluid channels is structured to be selectively driven by an actuator such that as the plunger including a plurality of axially incorporated fluid channels is axially displaced away from a first position the number of axially incorporated fluid channels in fluid communication with the fluid inlet and the fluid driven motor increases.