Answer Posted / ku
Normally the selection of the actuator is governed by the
maximum dp shutoff for any service, You have find out what
could be maximum possible inlet pressure to the control
valve and minimum possible downstream pressure, which will
provide you maximum delta P that your actuator should
handle, for example you have a column operating at pressure
P1 and a pump is taking suctionfrom this column and the
control valve is at outlet of the pump, the pump is
discharging this material to a drum with certain pressure,
in this case you will take the shutoff pressure of the pump
as inlet pressure and minimum pressure that can be at the
drum. This will automatically result in an actuator sizing
and selection suitable for this service. I am not sure why
you mentioned bigger size actuator as actuator should
be "big enough" to handle the maximum delta P across the
control valve.
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