Answer / instru

Bigger size actuator are required whenever thrust required
for control valve is higher. Thrust required is higher
whenver control valve has to open against high differntial
pressure. Also whenver type of packing is Graphite , large
size actuators are required because packing friction is
higher compared to PTFE.

Answer / 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.

Answer / rakesh kumar .n be

for high pressure application we use the the bigger actuator is wrong concept, mostly in the early days days we used this kind of actuator, mostly used for diaphragm and piston type actuator , if u use diaphragm type then u need big cascade, for high pressure , but we should change the cascade for regular intervel. in our company we control the 220 kg/cm2 of pressure in the small actuator only, bigger actuator is disturbance only large space is needed and difficult to calibrate. thanks

Answer / rahul

when valve size is more,
mostely for control valve

Answer / joby

if the valve is in higher size ,we have to go for higher
actuators for operating the valve.
FOR ESD VALVES
if the valve size is more than 18" mostly the suppliers
prefer hydraulic systems for operating the actuator
instead of air.The pressure required to operate the higher
size actuator will not be sufficient ,if you are using
plant air.

canu tell me why 4-20 ma and why not this 3-25ma?please give reason of this value.

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