Principles of on-site pressure gauges and positioners in control valves
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The control valve is operated manually, with the main controller sending a signal of 50. If the valve gets stuck at position 40 and the positioner fails to detect this, will the solenoid valve keep being activated in order to drive the diaphragm? The on-site pressure gauge measures the diaphragm pressure (pressure behind the valve), and the instrument air pressure is 0.7 MPa.
This is not a solenoid valve, but rather an electrical converter. Its function is to convert the input electrical signal into the corresponding output pressure that is used to open and close the pneumatic diaphragm control valve. A manual control signal is sent to the electrical converter; when the diaphragm control valve gets stuck, the pressure on the valve’s diaphragm does not increase, and it remains at the pressure corresponding to the electrical signal sent to the electrical converter. The pressure gauge in the figure appears to represent the output pressure of the electrical converter, as well as the diaphragm pressure of the pneumatic diaphragm control valve.
In other words, the output value of the control valve is ultimately converted into the corresponding pressure value. If it doesn’t have a self-travel detection function, then what is the purpose of the locator? Most control valves do not have a primary feedback function for monitoring the valve position on-site. In that case, won’t the locator be needed anymore?
Since the output is converted into corresponding pressure, is there a pressure detection signal available as an output value for self-checking?