# Level system of water tank?feedback of close loop? [duplicate]

I have attached a photo from animation from following link

https://beta.spiraxsarco.com/learn-about-steam/basic-control-theory/basic-control-theory

this photo shows a float in a water tank, it appears to be close loop controlsystem but how it is close loop system?where is feedback?

• If you have a general question about identifying open-loop vs. closed-loop control systems, you should make that your original question. Add these additional examples there, rather than creating a separate question for each one. Sep 4, 2019 at 13:36

## 2 Answers

The feedback is the float lever that changes position with respect to water height. The valve together with a fulcrum is proportional controller. If you change the fulcrum position, you actually adjust the proportional gain.

I do think that everything is very well explained in the link.

Close loop just means there is a response to a change in input, In that example, the float being raised higher by the water pushes a valve gate closed by a basic lever, so this can be considered a proportional only loop,

This is how most float valves work, the one in your toilet tank is a very close approximation if you need a physical example to understand it, if you push the float arm down a little, the valve opens and the tank begins to fill. once it reaches the level above where it is "full" the valve is forced shut by the force from the float.