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...

In control valve there are two type of valve seat we can use metal to metal seat & soft seat.On this valve seat i have following doubt. 1)I have never seen practically the internal assembly of valve so my doubt is that basically weather the seat is soft seat or metal its basic MOC is same as valve body(SS or CS) only in soft seat we are using PTFE ring & place on valve seat & in metal this PTFE ring is not threr am i correct??????? 2)what are the common general rule for using metal to metal seat & soft seat,means its depend on process parameter like liquid,gas, steam & on valve leakage class.

1 Answers  

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Name some of the common protocol use in automation.

3 Answers   Empower,

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need to calculate flow rate with the help of dp range and orifice bore dia and size. range is 0 to 400 inwc and orifice size is 12 inch 150 # rf and bore dia is 7.180 inch. need to calculation for flow rate

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field bus transmitter calibration procedure tell me

0 Answers   BAP,

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What inherent design and operating principles are included in a modern control system to use predictive maintenance practices to increase overall system reliability?

0 Answers  

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If a warning lamp will operate with the ground circuit is bypassed with a jumper wire to ground, what should you check?

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7 Answers   Schenck,

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3 Answers  

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tell about various protocols used in different plcs

3 Answers   Emerson, Samtel,

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We have a Yokogawa Micro-XL DCS, which is having around 300 I/O, but whenever there is any wire gets grounded in field, the 24v supply to all loops gets dipped & all the indications at DCS goes to IOP(shows input open), at present we have fixed 500mA fuses in all the lines but which does not working. Does it required to replace with lower amps fuse, then how much or is there any other solution for this.

2 Answers  

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what different types of problems do occur while doing instrumentation commisioning and how to solve them? please explain in detail

0 Answers   Process Control Technologies,

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TEMPERATURE VARIATION FOR FREQUENTLY.

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