I’d like to ask everyone questions regarding level control

It is possible to set a lower limit output value for the valve; if no such lower limit is specified, the valve will close.

If there is no minimum output requirement, will the valve close before the liquid level drops?

This post was last edited by jlshnlhj on 2023-8-16 at 11:16. In PI control, if there is no lower limit for the output, it is determined whether to turn it off based on the P and I parameters. Generally, when a low liquid level alarm is triggered, attention and human intervention are required.

If the feed valve is closed, the level gauge will detect a drop in the liquid level in the tank and send a signal to the discharge control valve to increase its opening degree, in order to maintain a stable liquid level. The discharge control valve will gradually increase its opening until the normal liquid level is reached. If the feed valve remains closed, the discharge control valve will continuously increase its opening until it reaches its maximum opening. When the liquid level drops to a low level, the opening degree of the discharge control valve may still not be zero, as the system needs to maintain a certain flow rate to keep the liquid level stable. But over time, if the feed valve remains closed, the liquid level will continue to drop until it reaches a low level, at which point the discharge control valve will close to prevent further discharge. Therefore, the opening degree of the discharge control valve will not keep decreasing until it closes, but it will eventually reach the appropriate opening degree at low liquid levels. .

If the controller has no output limit, the tank outlet control valve will remain fully closed.