Suitable restriction placed in flow stream causes a differential pressure across it.
As flow depends upon differential pressure (Head) & area, so any of them or both can be varied
for varying flow.
Suitable restriction placed in flow stream causes a differential pressure across it.
As flow depends upon differential pressure (Head) & area, so any of them or both can be varied
for varying flow.
For creating differential pressure : Orifice plate, Venturi Tube, Flow Nozzle , pitot tube
For measuring pressure : U-Tube Manometers, Ring–Balance Manometer, D.P. Cell
Process pressure is transmitted through isolating diaphragms and oil fill fluid to a sensing
diaphragm. The sensing diaphragm is a stretched spring element that deflects in response to
differential pressure across it. The displacement of the sensing diaphragm, a maximum deflection
of0.004 inch (0.10 mm), is proportional to the applied pressure. Capacitor plates on both sides of
the sensing diaphragm detect the position of the diaphragm. The transmitter electronics convert
the differential capacitance between the sensing diaphragm and the capacitor plates into a twowire,
4-20 mA dc signal and a digital output signal.
The control valve, commonly named the final control element of control contains a pneumatic device that converts the control signal from the controller in action, regulating the flow.
 ON - OFF SERVICES :- Gate, Ball, Diaphragm, Plug, Butterfly valves.
 THROTTLING SERVICES :- Globe, Butterfly, Diaphragm, Pinch valves.
 NON - REVERSE FLOW :- Check valves.
Following specifications are used for control valve
 Flow medium and operating temperature
 Flow rate kg/hr or Nm3/hr Max/Min/Normal
 Inlet and Outlet pressure : kg/cm2 Max/Min/Normal
 Max. allowable diff. Pressure : kg/cm2
 Density of medium : kg/m3
 Viscosity
 Cv : Valve Flow Coefficient
 Actuator, Body, Trim, Diaphragm, Diaphragm plate, Actuator stem
 Actuator spring, Seat, Travel Indicator, Valve stem, Gaskets, Yoke, Hand wheel
It is the flow of water (G=1, T= 6 to 34 deg. C) through the valve at full lift in U.S gallon per minute with a pressure drop across the valve of 1 psi.