Introduction:
Control valve is the heart of any unconscious process control system. It helps in controlling the process by choking the flow through it, thereby acting as covariant resistance in the process.
Principle:
In compressible fluid silklike inside a pipe passes through narrower area, accelerates by converting inner(a) energy pressure head into velocity head. After temporary the restriction, the velocity is again converted to pr. Head. But some of this pr. Cannot be recovered. Hence across any change in flux area there is always some pr. Loss. Control valves get going on the above basis.
control valve varies the pressure drop by relatively moving an element ( valve plug ) against a furbish up opening ( valve seat ).
Basis of control valve sizing: ( incompressible fluids)
Basis: bernouilli’s theorem
P1 p2
U1 u2
A1 a2
u2² - u1² = 2 gh
Expressing velocity interms of flowrate and area in the above equation and ignoring non-ideal influences, results in
Q = cv ( ∆p/ g - rudimentary liquid sizing equation
Where
Q = theoretical flow rate
Cv = through an experiment determined coefficient of valve
and is equivalent to water flow rate in usgpm when the pr.drop across the complete open valve is maintained at 1 psi.
∆p = pressure drop across the valve
G = unique(predicate) gravity
Basis of sizing ( compressible fluids ) :
In the case of compressible fluids ( gases, vapors ), these fluids expand on pr. Drop and hence the particular proposition weight of the fluid changes. Hence...If you want to get a full essay, order it on our website: Orderessay
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