VALVE MAGAZINE Summer 2025

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Flow Formulas (Non-Choked Turbulent Flow Only)

I. LIQUIDS

G ( ) V C v 2

dP G V

dP G

V = C v

C v =

dP =

Where: V = Liquid flow (gpm) dP = Pressure drop (psi) G = Specific gravity of liquid (water =1.0) Cv = Valve coefficient

( ) Q 1360C v

dP GT

P 1 + P 2 2

Q

2

II. GASES

dP = P 1 -- P 1 -- 2GT 2

Q = 1360 C v

C v =

dP GT

P 1 + P 2 2

1360

Where Q = Gas flow (scfh) dP = Pressure drop (psi) 1 T = Absolute temperature of flowing medium (degrees Rankine=°F + 460)

P 1 = Inlet pressure (psia) P 2 = Outlet pressure (psia) C v = Valve coefficient G = Specific grav ity of gas (air =1.0)

1 - 2 2 ( ) W 3C v

2

P 1 + P 2 2

W

III. SATURATED STEAM

C v =

W = 3 C v dP

dP = P 1 -- P

P 1 + P 2 2

dP 3

Where: W =Saturated steam flow (lbs per hour)

dP =Pressure drop (psi)¹ P 1 =Inlet pressure (psia) P 2 =Outlet pressure (psia) C v =Valve coeffi cient

1- For calculation purposes, dP should never exceed ½ the inlet pressure, P 1 .

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