is aligned with connected pipes to allow free flow through the valve in full open position the valve plug 12 is in an elevated position within the valve body wherein spaced apart circular seats 16 and 17 on the valve plug 12 are not in sealing engagement but are in close proximity with associated circular seats 18 and 19 secured to the internal surface of the valve body to move the valve plug 12 to a closed position the plug is rotated 90 degrees from the position depicted in fig1 and thereafter lowered to effect sealing engagement of the seats 16 17 with the seats 18 19 as depicted in fig2 the rotational movement of the valve plug 12 between open and closed positions and the axial movement of the valve plug to an elevated or lowered position is difficult and requires special complex mechanical devices to accomplish the required movements to this end there is provided a fluid actuator 20 which is operably connected to a valve stem 15 associated with the valve plug 12 as shown in detail in fig3 the actuator 20 includes a body portion 21 provided with an axial bore within which a lift piston 22 is axially movable within a first cylinder or chamber 23 formed in lower portion of the bore of the body 21 the lower end of the piston 22 is formed with a depending stem 24 the piston stem 24 extends through a suitable axial aligned opening formed in a base plate 26 an axial bore 27 in the piston stem 24 receives the extending end of the valve plug stem 15 a pin 28 establishes an operative connection between the cooperating engaged parts extending upwardly from.