English to Greek Tech/Engineering Electronics / Elect Eng technicians' course

The flow rate (F) which passes through the valve depends not only on the valve opening but also on the difference AP of the pressures and P^ across the valve, according to the equation:XXXXX
It may occur that is not constant, e.g. because of changes in the pressure P on the ceiling of the storage tank, and P^ is not constant, owing to variable conditions in the downstream system. In this instance, the correspondence between the flow rate which passes through the valve and the valve opening is invalidated and, consequently, between the controller output and the flow rate.All this disturbs the level control. Such disturbance can be eliminated by the CASCADE CONTROL