What are the direct and reverse actions of the actuator in a pneumatic diaphragm control valve?
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I’m a newcomer to the workplace and not familiar with many things; I hope those who are more experienced can give me some guidance. Thank you
Simply put, it refers to whether the valve opens more or closes more when the signal increases; the former is direct action, while the latter is reverse action
For most control valves, direct-acting type: the air supply enters the diaphragm head from above； Reaction: The air supply enters the membrane head from below
The positive and negative actions of a regulator are defined as follows: These can be determined by the controlled system and negative feedback. When PV > SV, MV needs to be increased, which indicates that the controlled system is of the negative type and the regulator is of the positive type, resulting in negative feedback； When PV > SV, MV needs to be reduced; this indicates that the controlled object has a positive value while the regulator has a negative value, resulting in negative feedback. A more detailed definition is shown in the figure below: wherein PV is the gas source pressure, and SV is the valve pressure. A regulator is a controller that compares the measured values of process parameters with set values; once a deviation is detected, it generates an output signal in accordance with certain control rules to actuate an actuator and eliminate that deviation, thereby keeping the parameter within close to the set value or changing it according to a predetermined pattern.
It’s about determining whether the valve operates on air opening or air closing principle
Positive action: when air is supplied, the valve stem moves downward, that is, it is a air-actuated shut-off valve； As a reaction, when gas is supplied, the valve stem moves upward, that is, the valve opens under gas pressure ；