It depends on how far above the conduit the liquid level is, what pressure we've got, things like that.

The roof rises and falls with the liquid level in the tank.

Surface foam may cause problems with liquid levels and give overflow.

The difference in liquid level represents the applied pressure.

A computer will monitor liquid levels, pump speed, pressure and the like, and make adjustments.

Sensor(s), which measure some physical state such as temperature or liquid level.

The other tube is designed to sit above the liquid level as a means to warn against overfilling.

The liquid level rises as air leaks out through the bed.

An air bubbler system uses a tube with an opening below the surface of the liquid level.

The higher the liquid level above the producer the lower the temperature and higher is the sub-cool.