The hydraulic system is a closed circuit (loop) (fig. 2.3.3.1, 2.3.3.8) made of a pump which moves the water from a stainless steel container up to the target manifold and back to the container by means of stainless steel tubes. In order to produce a stable film a gear pump, magnetically coupled to a dc motor, is used.
A tackometer which is on the pump axis measures the pump speed (turn/min) and a flowmeter, just before the entrance of the scattering chamber, measures the flow rate. Moreover the command voltage value is read, although it is redundant. By continuously measuring these parameters, and comparing them, one can essentially monitor the target thickness stability.