Answer / mohamed yousuf(instrumentation

according to the formula P=F/A

Actually we are applying the 2.5 bar pressure to the
diaphram actuator. By increasing the area of diaphram we
can increse the force acting on the diaphram and that muuch
of force is more enough to actuate the stem movement.even
though 40 bar pressure is applied only to the small area
(plug of the control valve).the force actiong on it will be
very small.

Answer / waseem ahmad

Mr. Bipinchandra is right but there are more possible
answers to this. 1) what is the differential pressure across
the valve? the pressure of steam might be 40kg but the
pressure of steam across the valve might not 40kg. 2) the
use of balanced plug in control valves allow us to control
high pressure fluids with minimum actuator force.

Answer / centhile r mohan

the 2.5 bar is used to control the valve by giving it to
the diaphragm to actuate it.so the process pressure 40bar
is controlled.

Answer / bipinchandra ravalia.

The 2.5 bar used to control the valve acts on the
Diaphragm. Now the area of the diaphragm is Large and thus
the Force Per Unit Area acting on the stem is very much
greater than the Process pressure of 40bar. Thus it is not
difficult to control this process pressure with the given
2.5 bar air supply to the control valve.

Answer / sagar,kptl

By using of pneumatic control valve,that control valve have a helical spring containing tension when give pressure 2.5 bar. That pressure force acting will control the 40 bar steam

.'.P=f/a

Answer / rajender

By using Pneumatic Control Valve(Plug valve)

Answer / r_vaya

That's why in high pressures line(like super heater's  steam in power plant)  having double seated globe valves.therefor double seated plugs has line pressure both side equal (upside same and down side same ) is equal to line pressure 0 
So thus, plug will operate according valve's pressure.....

Answer / ramesh4529

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