How Control Valve works?

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How Control Valve works?for beginners

Control valves are used to control Pressure, Temperature, flow or Level in any process plant, within a required operatingrange to ensure the quality of the endproduct.

How Control Valve works?Lets take an oil-gas separator as an example.

Oil GasSeparatorthis separator discharges gas, and a gas discharge valve (red valve) is put for this purpose.and it is equipped with a pressure gauge PG

PG

How Control Valve works?Lets say we want to maintain the separator pressure at 70 psig

Oil GasSeparator the operator will keep in his mind this pressure and will close and open the RED valve slightly to maintain the pressure at 70 psig

70 psig

How Control Valve works?

Oil GasSeparatormaintain the pressure at 70 psig

70 psig

the operator will always make a comparison between the PG and the 70 psig in his mind, and will take action on the valve according to this comparison

If you want replace this manual valve with a Pressure Control Valve PCV

How Control Valve works?the Pressure Gauge PG will be replaced with a Pressure Transmitter PTthe operator will be replaced with a Pressure Indicator Controllerthe 70 psig in operator mind is the Set Point SP

PT

SPPICthe setpoint will be inputted by the operator

How Control Valve works?

PT

SPPICIn the auto control system, the PIC receives a signal from the PT, then compares it with the set point SP, then takes an action, either by closing or opening the valve to achieve the set point.

Take a look at this control system, the pressure vessel is controlled by a PCV. The PIC compares the SP with the PT reading, then gives a signal to the PCV electronic signal, this electronic signal is transferred to Air Pressure through an I/P current to Press.

another example but more complicated.in this control system, temperature is controlled by a TIC which takes a signal from a TI then controls 2 FCVs to control the temperature out of heat exchanger.

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