Answer / anwar mydeen

Air to open valve: the pneumatic valve will open when the
air is applied in to the actuator chamber. and the valve
will goes to close condition when u remove the pneumatic air.
In oil industry oil outlet and produced water outlet control
valves are air to open valves.

Air to Close: the pneumatic valve will close when the air is
applied in to the actuator chamber and the valve will goes
to open condition when u remove the pneumatic air.

Answer / mohammed abdul rahman

This query is mostly related to pneumatic diaphragm actuated control valves. Air to open valves have the pneumatic input on the under-side of the diaphragm with a spring on the topside, which causes the valve to open on increase in control signal. Air to close valves will have the pneumatic input on the topside of the diaphragm with a spring on the under-side to provide counter force.
An i/p converter will convert the 4-20mA signal from control system to an equivalent 3-15psi pneumatic signal to actuate the control valve.
A positioner will have the i/p converter inbuilt and is connected to the moving part of the valve and automatically adjusts the signal to the actuator to maintain a position proportional to the signal. This introduces a loop inside a loop.
Please refer the control valve handbook from Fisher for reference. It is available as a free download.

what is cavitation ?

7 Answers  

---

what does a positioner in control valve ?

11 Answers  

---

I am teja. I am studying Msc(tech) Electronics and Instrumentation (3years course) in Andhra university. But my course is not recognised by UGC and AICTE. Please tell me the job opportunities after this course. And i fineshed PLC course in IGIAT ,Vizag.Also complted my short term coure in SCADA, Seimans WinCC in ATI,Hyd.After Msc can i join Mtech for good job? or phd. How i can get good job in INdustrial Automation Side. Please give replay.Because this is my life matter.

0 Answers  

---

How can we say that accuracy of measurement increases by using 3 or 4 wire RTD? because for example: If resistance of RTD element is say r ohms and Resistance of the cable from transmitter to RTD is R ohms And if 4 wire RTD is used, ____._____________________ R ohms | |_____._____________________ R ohms / \ / r ohms \ \ | |______.__________________ R Ohms | |_______._________________ R ohms Then the actual resistance measured will be: Total = r + R/2 + R/2 = r +R Ohms Note: r+R instead of r ohms. hence error

2 Answers  

---

why metallic housing is provided of solenoid valve.

1 Answers   HPCL,

---

How much should be the values and/or percentages of these given below factors for a good controller ? Steady state error Delay Rise Time Overshoot Peak Time Settling Time Damping Oscillations & vibrations thanks

1 Answers  

---

how to know power plant process with corresbonding laws&thoeries

1 Answers   Bhel,

---

Is SmartPlant Instrumentation taking advantage of the quality assurance procedures within Intergraph?

1 Answers  

---

Technician A says that a fuel tank sending unit will have a high resistance only when the tank is full. Technician B says that its resistance when the tank is full depends on whether the sending unit is designed for use with a bimetallic gauge or with a magnetic gauge. Who is correct?

3 Answers  

---

how many types of preheaters are in cement industry & what r they can any body explain?

0 Answers  

---

Is it ok, to use non-contact type Radar type LT, on a tank that is half circular from the bottom side? If yes the, isn't the waves gonna bent in other directions? 

0 Answers   Process Control Technologies,

---

what is orifice plate? Give me best answer?....plz

5 Answers  

---