Seeking advice on actuators

This way of learning is not advisable; it is recommended to abandon such mnemonic-based learning methods and instead address the specific needs of each valve individually. Here it only includes the control of the valve by the remote control system, as well as the manner in which changes are applied to the positioner. So it’s better to learn one-on-one*.

This post was last edited by rickey on 2019-7-9 08:40. When the force increases, the downward movement of the push rod is referred to as a direct-acting actuator； When the signal pressure increases, a push rod that moves upward is called a reaction-type actuator. When a valve assembly and an actuator are combined to form a control valve, a air-operated valve gradually opens as the signal pressure increases; when there is no signal, the valve remains in a closed state ； A pressure isolation valve gradually closes as the signal pressure increases, and remains in an fully open state when there is no signal. A valve that opens when there is air (signal pressure) is called a pneumatically operated valve; once the signal is interrupted, the valve returns to its original state (closed). A valve that can be closed only when there is air pressure (signal pressure) is called a pneumatic shut-off valve; once the signal is interrupted, the valve returns to its original state (open). The direct/indirect action refers to the operating principle of pneumatic regulators; it is unrelated to pneumatic control valves. However, pneumatic regulators with direct action are usually equipped with control valves that operate in a shut-off manner ； Reactive pneumatic regulators are usually equipped with a regulating valve for air distribution.

The action type has no inherent relationship with air-open or air-close, as the valve seat design can also change a direct-acting air-open type into a direct-acting air-close type.

This applies to linear stroke control valves. On the 3rd floor, it was already explained what the forward and reverse actions of the actuator are ； There is no such thing as a \"forward or reverse action\" for the valve body itself; only the terms \"correct installation\" and \"incorrect installation\" apply. When assembling a control valve, when the valve core is installed from top to bottom, it is considered correct installation; conversely, when the valve core is installed from bottom to top, it is considered incorrect installation ； As for their combination patterns, their structure determines that they are indeed \"positive-positive (gas-shut type), positive-negative (gas-open type), negative-positive (gas-open type), and negative-negative (gas-shut type)\". Taking the \"positive type (air-operated)\\" as an example: A positive-acting actuator means that when air is supplied, the push rod moves downward, causing the valve core to move from top to bottom, thus moving the valve in a closing direction (the specific structure can be seen in its cross-sectional view). In other words, it is an air-operated valve, i.e., of the air-operated type.

The valve stem is moving downward, the valve core is in the correct position, and the valve is closed. So it’s a gas shut-off valve.