A dual piston valve actuator operable to provide an initial thrust force that is greater than a subsequent thrust force for moving a gate valve from a closed position to an open position. The actuator may include a first piston and a second piston movably disposed within a bore of the first piston. The first piston may define a first piston area for proving the initial thrust force, and the second piston may define a second piston area (that is less than the first piston area) for providing the subsequent thrust force. Movement of the first piston is limited relative to the second piston for moving the gate valve using the initial thrust force an initial portion of the valve stroke, while moving the gate valve using the subsequent thrust force the remaining portion of the valve stroke.