Answer / sridhar

if the flow must be maintained in process line, we can use
the double acting control valve. for example,if there is a
purging system for any process control,even if the signal
fails and air fails, the valve should be in same poistion
to maintain the flow in the pipe line for process safety.

Answer / carl_ellis

Part of your problem is your terminology.

Valves are chunks of machined metal and elastomers, valves
are not single action or double action, the actuator that
moves the valve stem is.

So your Google search should be for double action actuator,
which will provide you an answer.

Carl Ellis
Measure First

Answer / afroz

I need answer

Why we use DPT? can we use PT instead of DPT?

2 Answers  

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why we use 4-20 mA for calibration of the instruments.why we cant use 0-20 mA?

5 Answers  

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without a positionar can a control valve operate? give the difference of operating with positionar and without positionar?

5 Answers   IOCL,

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if a tank is contaning oil and water than how can we measure the oil and water level seperately

3 Answers  

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what are the different types of Protocols? & their applications.

6 Answers   Infosys, Sitara Chemical Industries, Syntel, VSNL,

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Related to control system, What is difference between 4-20 mA active & 4-20 mA pasive signal.

1 Answers  

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Somebody ask me how many size of control valve what is mean of control valve size?

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whats the working of principal thermocouple

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HOW TO CALIBRATE A PRESSURE SWITCH?

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Square root calculation for dp flow transmitter?

0 Answers  

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Sir , i have completed my M.Sc In Instrumentation and presently working in Maintenance department 3 yrs Exp , is there is any possible for work in offshore ..

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why 4-20 mA in covection system?

3 Answers  

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