Gas pneumatic valve and gas breath what is the definition of a fixed valve?

with pneumatic actuators signal pressure increases, the push rod downward movement is acting actuators; Signal pressure increases, the push rod upward movement called reaction type actuator. Pneumatic valve components and actuator pneumatic valve, regulating qi pneumatic valve is as the pressure signal, gradually open, no signal, pneumatic valve closed; Gas breath valve is as the pressure signal, gradually closed, no signal, pneumatic valve in the fully open position.

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