Rotary actuators are used as part of some mechanical devices, to deliver rotary motion in an efficient manner and with the capability to maintain rotary position by blocking the hydraulic power fluid source.  The ability to maintain a rotary position is desirable to control aircraft flight control surfaces and for other applications such as rotary valve assemblies.  Rotary actuators are desirable because they maintain constant torque and conserve space.  Such prior art rotary actuators typically include multiple subcomponents such as a rotor and two or more stator housing components.  These subcomponents generally include a number of seals intended to prevent leakage of fluid out of the housing and/or between hydraulic chambers of such rotary valve actuators.  Because of this leakage, prior art rotary actuators cannot maintain position by merely blocking the hydraulic power source, but maintain position by supplying additional make up fluid and constant control.