What is the relationship between the forward and reverse actions of pneumatic devices and air-operated open/air-operated closed functions?
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What is the relationship between the forward and reverse actions of pneumatic devices and air-open and air-close functions? Positive action refers to air-operated shut-off valves, while negative action refers to air-operated open valves?
Positive action means that when air is supplied to the actuator, the push rod moves downward; the opposite is negative action. The valve body can also be installed in either a positive or negative orientation – with the valve stem moving downward to close the valve in the positive orientation. Whether the valve operates on air pressure to open or to close depends on both factors; for example, a positive-action valve with a positive installation orientation is a valve that closes under air pressure
Direct action (the valve stem moves downward as the air pressure increases, ZMA); reverse action (the valve stem moves upward as the air pressure increases, ZMB). In a gas-operated valve that opens fully when there is no pressure signal from the gas source, and gradually closes as the pressure signal increases, it is referred to as a gas-close type valve. When there is no pressure signal from the air supply, the valve remains fully closed; as the air supply signal increases, the valve gradually opens – this is known as a air-operated type valve. Such as the air-operated diaphragm control valves in air-open and air-close types:
In pneumatic actuators, a positive action occurs when an increase in signal causes the valve stem to extend, while a reverse action occurs when an increase in signal causes the valve stem to retract. Control valve: A valve whose opening increases as the signal increases is an air-open valve, while a valve whose opening decreases as the signal increases is an air-close valve. The valve core can be installed in the normal orientation or the reverse orientation. When a direct-acting actuator is used with a normally closed valve core, it results in a air-shut valve; when used with a normally open valve core, it results in an air-open valve ； When the reaction actuator is paired with a normally open valve core, it becomes an air-operated open valve; when paired with a normally closed valve core, it becomes an air-operated closed valve.