The fixed ball valve shall select the front sealing structure, the rear sealing structure or the front and rear double sealing structure according to the pressure, medium property and sealing requirements. The valve seat material of medium and high temperature ball valves can be polystyrene or metal.

The time allowance given by the thermal capacity of the motor shall be considered for the above three modes. It is difficult to make it consistent with the thermal capacity characteristics of the motor in a single way. Therefore, it is necessary to select a method that can act reliably according to the cause of overload - combined composite mode to achieve comprehensive overload protection. The mine explosion-proof pneumatic butterfly valve motor has a thermostat embedded in the winding with the same insulation level as the motor. When the rated temperature is reached, the motor control circuit will be cut off. The thermal capacity of the thermostat itself is small, and its time limiting characteristics are determined by the thermal capacity characteristics of the motor, so this is a reliable method.