Burkert 8626 Instructions De Service page 16

The system must not be dimensioned so closely with regard to the
NOTE
flow coefficient (k
the available pressure drop is used up there, and then the nominal
valve diameter of the MFC is chosen so great (k
the small remaining part of the pressure is dropped over the MFC. In
this case, the valve authority would be too small and only a small
part of the working range of the valve utilized. That could be greatly
detrimental in general to the resolution and control performance.
If the system has been dimensioned „to closely", increasing the
nominal diameter of the MFC valve does not help. In this case an
increase either in the admission pressure or the k
made, e.g. by increasing the pipe diameter, to keep the valve
authority within the permitted range.
When the device is operated within the specified pressure range, the proportional
valve assumes the functions of both control and tight closure.
16 - MFC/MFM
) that at the desired flow rate, the major part of
Va
>> k ) that only
Vs Va
value should be
Va