What do the terms “forward” and “reverse” action refer to in control valves?

The positive/negative action refers to the operating principle of pneumatic regulators; it is unrelated to pneumatic control valves. However, pneumatic regulators with positive 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 answer on the 2nd floor is correct. The so-called positive and negative reactions are mechanisms established to ensure safety in case of sudden accidents.

These are all determined by process requirements; some processes require that the valve be in an open or closed position when there is no power supply (i.e., no gas).

1: Definition: Direct-acting control valve: When the valve body is in an upright position and the valve core is installed in the correct orientation, if the valve core moves downward resulting in a reduction of the flow area between the valve core and the valve seat, it is called a direct-acting control valve. The poster is correct; this is indeed the definition of a control valve. 2: In DCS, the terms \"direct action\" and \"reverse action\" refer to the fact that when we set the control valve to 0 in the control room under direct action (or reverse action), the valve’s opening degree is 0 at the site (with reverse action resulting in an opening degree of 100). 3: When selecting a control valve, it is necessary to choose between air-operated open or air-operated closed valves from a safety perspective; for example, the self-regulating valve used for venting gas in hydrogenation units is an air-operated closed valve, which serves to ensure timely prevention of air leakage in emergency situations... Direct-action control valves: The air pressure signal enters from above the diaphragm, causing the valve stem to move downward. Reverse-action control valves: The air pressure signal enters from below the diaphragm, causing the valve stem to move upward. Large-diameter control valves are mostly of direct-acting type, while small-diameter control valves are mostly of reverse-acting type. :victory:

You’re absolutely right; it’s a learning post! But it’s meant to be shared ! ! ! ! You guys started discussing this here

They are essentially what are known as air-open valves and air-close valves. The feed valves are usually air-open valves, while the discharge valves are typically air-close valves, mainly for safety reasons.

Regarding the normal and reverse operation of the valve, this depends on your process requirements. Under normal conditions, it operates as described by the original poster, but in emergency situations, there are valves that open when air is present and those that close when air is present

Regarding the 9th floor, it’s just about turning the wind on and off, I think. When the wind is on, it stays on; when the wind is off, it shuts off