Is the body and bonnet, stem, plunger, hole, sealing and handwheel etc parts. When the handwheel rotation, through the valve stem drive plunger piston valve in the hole and reciprocating movement among frame to complete the valve open and close function. Piston valve performance is the following: (1) rated output force or pneumatic device should comply with the GB/T torque and GB/T 12223 12222. 2 piston valve in the racing for cylinders on table 2 of input pressure, its action should be stable, no resistance and reptiles. 3 in 0.6 MPa piston valve of air pressure, the pneumatic device or close two directions of the output torque or thrust, its value should be no less than the sign of pneumatic device, and action should be flexible values, don't allow each place appears permanent deformation and other abnormal phenomenon. 4 piston valve seal to experiment with the maximum working pressure testing, from their own back pressure leak out side the air quantity does not allow more than (3 + 0.15 D/min (standard) cm3 state), From the rear, the output shaft leakage air volume of not allowing more than (3 + 0.15 d/min) cm3. 5 piston valve strength test of 1.5 times with maximum working pressure testing, keep 3min test pressure, the cylinder cover and static sealing parts are not allowed to have leakage and the structural deformation. 6 piston valve movements, pneumatic device simulation life in valve, two directions of the output torque or thrust ability circumstance, open the open-close operation shall be not less than 50,000 number (rev - closed cycle for a). 7. Piston valve of pneumatic device with buffering mechanism, when the piston moves to the schedule, don't allow terminal shock