16 - MFC/MFM
english
When the device is operated within the specified pressure range, the proportional
valve assumes the functions of both control and tight closure.
NOTE
The system must not be dimensioned so closely with regard to the
flow coefficient (k
Va
) that at the desired flow rate, the major part of
the available pressure drop is used up there, and then the nominal
valve diameter of the MFC is chosen so great (k
Vs
>> k
Va
) that only
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
Va
value should be
made, e.g. by increasing the pipe diameter, to keep the valve
authority within the permitted range.
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