Abstract: A compact valve actuator for operating a valve of the butterfly type or the like. The actuator comprises a pair of joined pistons which respond by simultaneous reciprocation to introduction of operating fluid such as air into the actuator. Means such as a linkage for connecting the actuator to a valve is provided, such means being connected to the pistons interiorly thereof for minimizing the actuator size for a given required stroke. One of the pistons at a bearing surface thereof, rides on a guide means received interiorly of the piston thereby further enhancing the compactness of the actuator. The surface of the guide means is pressurized with the operating fluid applied to that one piston whereby risk of operating fluid leakage across that piston at the bearing surface thereof is substantially eliminated.