# Pressure drop calculation in valve (Instrumentation & Control)

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## Pressure drop calculation in valve

For Pressure drop calculation in valve to understand. Keep the important points in mind.
• Pressure drop is directly proportional to the flow rate of any liquid and gas. If the flow rate is high pressure drop will be more and vice versa.
• The important thing in valve is flow coefficient of valve (Kv or Cv) . Manufacturers publish the flow coefficient in instrument or valve data sheet.
• When we are doing calculation  in  Metric units then flow and pressure units will be m3/hr and Bar or l/s and kPa and flow coefficient is Kv.
• In imperial units flow and pressure units are gpm and PSI and the flow Coefficient is Cv.

Formula of pressure drop in valve
Pressure Drop= (36Q/Kv) 2
Q is the flow rate in l/s.

Example
Calculate the pressure drop if the flow rate 0.355 passes through a valve.
Valve data:
Valve type D921 DRV ( Double regulating valve ) with flow coefficient (3.61)
Solution
Pressure Drop= (36Q/Kv) 2
= (36×0.35/3.61)2
=6.98 kPa
This is the pressure drop across the valve. In this lecture we used Kv not Cv because it is more common.