2、 Operating principle of pneumatic actuator:
1. When the compressed air enters the pneumatic actuator from nozzle A, the gas pushes the double pistons to move in a straight line towards both ends (cylinder head end). The rack on the piston drives the gear on the rotating shaft to rotate 90 degrees counterclockwise, and the valve is opened. At this time, the gas at both ends of the pneumatic actuator valve is discharged with nozzle B. On the contrary, when the compressed air enters both ends of the pneumatic actuator from the nozzle B, the gas pushes the double plug to move in a straight line in the middle. The rack on the piston drives the gear on the rotating shaft to rotate 90 degrees clockwise, and the valve is closed. At this time, the gas in the middle of the pneumatic actuator is discharged with nozzle A. The above is the transmission principle of the standard type. According to the user's needs, the pneumatic actuator can be installed in the opposite transmission principle to the standard type, that is, the valve is opened when the alignment shaft rotates clockwise, and closed when it rotates counterclockwise. Single acting (spring return type) pneumatic actuator nozzle A is the air inlet, nozzle B is the exhaust hole (nozzle B should be equipped with a muffler). The air inlet of nozzle A is to open the valve, and the valve is closed by spring force when the air is cut off.
2. The single action here means that the cylinder is reset with a spring. When gas failure or power failure occurs, the valve is reset by the spring in the cylinder to close or open the valve. (Normally closed or normally open optional). Double acting means that the cylinder is opened and closed by compressed air.

Blind plate force of compensator fixing support
After the heat supply pipeline device is put into operation, because the pipeline is heated by the heat medium and causes the pipeline to stretch, measures should be taken to compensate the thermal elongation of the pipeline. The compensation methods mainly include the following: natural compensation, casing type compensator, bellows compensator, square or spherical compensator, etc. This paper mainly describes the comparison between the commonly used sleeve type compensator and the new thrust free rotary compensator in engineering cost and operation safety.
1、 Introduction to sleeve type compensator: it is a compensator suitable for straight laying pipeline, which is used to compensate the thermal elongation of pipeline between fixed supports.
For pipes with sleeve type compensators, the thrust on the fixed support is generated from the following aspects.
(1) Degree thrust Pg · m Pg · m due to friction on sliding support= μ In the qL formula, q － calculate the weight of pipe section per unit length? Quasi 529 × 7 rock wool insulation, water filling q=367.92 × 9.8N · m; μ－ Friction coefficient, steel to steel μ＝ 0.3, steel and PTFE plate μ＝ 0.1； L - length of calculated pipe section, m;
(2) Thrust force generated by friction force of sleeve type compensator;
(3) The degree of thrust caused by uneven internal pressure, such as sleeve type compensators are set at both ends of the fixed support, but their pipe diameters are different; Or one end of the pipe section at both ends of the fixed support is provided with valves, blanking plates and elbows, while the other end is provided with sleeve type compensators; When the hydraulic test or operation of the pipeline is stopped, the unbalanced axial force of the pipeline will appear.