How are the open, close, and stop buttons for the electric valve implemented on-site?
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Which expert has a good understanding of electric valves? There is a valve at the tank base site, which is likely an electric valve. It is controlled by 3 DO points (digital output) in the DCS, for opening, closing, and stopping. Could some expert explain the principle behind this? PS: Clicking “Start” should control the motor to slowly open the valve, while clicking “Stop” should stop it (at the position it is in). How is this achieved? Is there a hold function?
The poster has provided too little information; it would be best to attach a wiring diagram so that someone can possibly answer. I’ve never seen control valves with settings for on, off, and stop. There are generally two types of control valves: one is a control valve with servo amplification, where the input is an analog signal ； One type is a control valve without servo control; it receives 220V signals for turning on and off, with no stop signal. The control valve operates when it receives such signals and stops when no signals are received. I have never seen a situation where a separate stop signal is required.
The actuator of this electric valve is of a very old design; it can be controlled using electrical circuits for forward and reverse operation – sending a signal to make the actuator move forward, and another signal to make it move backward. The circuit is used to stop the actuator’s operation
Just like an electric hoist: up, down, stop
If the DCS has 3 DO points and no other output points, then it has no regulating function at all; when it’s turned on, it’s fully on, and when it’s turned off, it’s fully off. There is no such thing as stopping at a certain level as you mentioned. I’m not sure what you mean by ‘stopping’ – it depends on the wiring of the valve and its instructions
You can think of it as a motor that can rotate in both directions. The electric actuator panel can be set to accept either a “momentary” or “pulse signal”. “In ‘pulse’ mode, both pulse on/pulse off are effective when closed; once the signal is disconnected, it stays in the ‘final’ position. It is not necessary to connect this type of stop signal. “For “Pulse signal”: both Pulse On/Pulse Off are valid when closed. Once the valve is in place (or the torque is reached), the motor will stop automatically; this is an internal function of the motor head that requires configuration. Two-position on/off valves generally use the second configuration. If the operation needs to stop at a certain position, then a stop signal must be applied, which is also a pulse. @jiaguoyun
It can be understood in this way. The DO signal that is activated starts the motor inside the electric valve; once the valve is fully open, the travel switch located inside the valve turns off the motor. The DO signal for closing triggers the reversal of the motor inside the electric valve; once the valve is fully closed, the internal travel switch that indicates the valve is in the closed position shuts off the motor. Stop means cutting off the power to the motor, so that the valve remains at a certain opening degree.