The issue of the distance between the nozzle and the baffle in pneumatic control valves
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If the distance between the nozzle and the baffle of a pneumatic control valve decreases, does the output pressure increase?
It can only be said that under the condition that the nozzle baffle mechanism is functioning properly, this is the case most of the time. In some pneumatic devices, the reversal of action is achieved simply by switching the air circuit; in this state, as the nozzle flap moves closer, the output decreases ； When the nozzle baffle mechanism is not assembled properly, it can occur that the nozzle baffle moves closer together (sometimes seemingly so), resulting in a decrease in the back pressure at the nozzle outlet.
Zeroing the pneumatic control valve also involves adjusting the distance between the baffle and the nozzle, right? Generally, I set the valve to manual mode and then zero it out; if there is no noticeable movement of the valve stem, I adjust the constant orifice
What is the relationship between the forward and reverse action of pneumatic actuators and air-operated open/air-operated closed valves? Does forward action refer to valves that open when powered by air, while reverse action refers to valves that close when powered by air?
What is the relationship between the forward and reverse action of pneumatic actuators and air-operated open/air-operated closed valves? Does forward action refer to air-operated closed valves, while reverse action refers to air-operated open valves?
The positive and negative action of a valve positioner refers to whether the pneumatic signal output increases (positive) or decreases (negative) as the input signal to the positioner increases. The counteraction of the positioner is rarely used; it is commonly required for ensuring the safe state of the valve in cases of power or gas supply failures, as well as to prevent adjustments to the forward and reverse actions of the regulator when switching between the primary, secondary, and cascade control schemes in cascade control.
For mechanical valve positioners, zeroing adjusts the initial position of the nozzle baffle, while the range setting determines the amplification factor of the lever mechanism； The constant orifice on the nozzle baffle can change its sensitivity, but its effect on the zero point and range is actually uncertain. Except in cases where the constant orifice used to block the nozzle baffle is deliberately used as a means of adjustment (for adjusting the amplification factor or range of the pneumatic amplifier) – which is common on some imported mechanical positioners – try not to adjust the constant orifice.