Abstract: An actuator which uses a double-ended hydraulic spring to propel an internal combustion engine poppet valve back and forth between a closed and an open positions. Timed delivery of supplemental pressure to a separate latching piston provides a means to fully "re-cock" the rebounding springs in each position. Activation is accomplished by releasing the supplemental pressure to allow the compressed fluid spring to propel the poppet valve in either one of two directions. A valve arrangement is also provided to allow a timed bypass of fluid around the latching piston during most of its transitioning to minimize the quantity of high pressure fluid consumption to that which is required to overcome friction losses.