Answer / carl_ellis

Yes, a pneumatic actuator can drive a valve without a
positioner.

In the HVAC world it's done all the time because the service
conditions (temperature/pressure/wear factor) for, say, a
chilled water valve does not necessarily demand the
precision control that a positioner offers.

An I/P (a current to pneumatic transducer) is used to
convert a 4-20mA control signal to a pressure control signal.

The service required in heavy process industries is usually
sever enough that a positioner is used on a control valve.

Company and industry practice will determine the use of a
positioner.

Answer / ajaya kumar behera

Yes we can only fully open/close by changing instrument air supply from header valve

Answer / tickno

yes it can ,but if the bench set of CV is on range 3-15 psi(instrument standadt unit,conversion from 4-20mA to 3-15 psi)

Answer / vergel

No, that is why i call a control valve, we need positioner to control the position of the actuator, if its a simple on off valve, no need for positioner...

plz tell me clearly about PID.."when v have to change I value,D value,GAIN??

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