Valve Sizing for Gas and Steam

Written by Jerry Ratzlaff on . Posted in Valve

Gas Flow Rate Formula

\(\large{ Q_g = 59.64 \;C_{vl}\; p_i \;\sqrt {\frac {\Delta p} {p_i} }  \; \sqrt {\frac {520} {SG\; T_a} }   }\)   

Where:

\(\large{ Q_g }\) = gas flow rate, SCFH (Use only at very low pressure drop \(\large{\left( \frac {\Delta p} {p_i} \right)}\) ratios of 0.02 or less)

\(\large{ C_{vl} }\) = liquid sizing flow coefficient

\(\large{ p_i }\) = valve inlet pressure, psia

\(\large{ \Delta p }\) = pressure differential, pressure drop across valve, psi

\(\large{ SG }\) = gas specific gravity (air = 1.0)

\(\large{ T_a }\) = absolute temperature absolute temperature of gas at inlet, degrees Rankine

 

Critical Flow Rate Formula

\(\large{ Q_{cr} = C_{vg}\; p_i \;\sqrt { \frac {520} {SG\; T_a} }   }\)   

Where:

\(\large{ Q_{cr} }\) = critical flow rate, SCFH (Use only to determine critical flow capacity at a given inlet pressure)

\(\large{ C_{vg} }\) = gas sizing flow coefficient

\(\large{ p_i }\) = body inlet pressure, psia

\(\large{ SG }\) = specific gravity of fluid (water at 60°F = 1.0000)

\(\large{ T_a }\) = absolute temperature of gas at inlet, °R

 

Universal Gas Sizing Formula

\(\large{ Q_g = \sqrt { \frac {520} {S\; T_a} }  \;  C_{vg} \;p_i\;sin \left[ \left( { \frac {59.64} { c_i} } \right)   \;  \left( \sqrt { \frac {\Delta p} { p_i} } \right) \rightarrow \right]           rad }\)   
\(\large{ Q_g = \sqrt { \frac {520} {SG \;T_a} }   \;  C_{vg} \;p_i \;sin \left[ \left( { \frac {3417} { c_i} } \right)  \;   \left( \sqrt { \frac {\Delta p} { p_i} } \right) \rightarrow \right]           deg }\)   

Where:

\(\large{ Q_g }\) = gas flow rate, SCFH

\(\large{ SG }\) = specific gravity of fluid (water at 60°F = 1.0000)

\(\large{ T_a }\) = absolute temperature of gas at inlet, °R

\(\large{ C_{vg} }\) = gas sizing flow coefficient

\(\large{ p_i }\) = body inlet pressure, psia

\(\large{ C_i }\) = \(\large{\frac {C_{vg}} {C_{vl}} }\)

\(\large{ \Delta p }\) = pressure differential, psi

 

Steam or Vapor Flow Rate Formula

\(\large{ Q_{sv} = 1.06\; \sqrt { \rho \;p_i }   \;  C_{vg}  \; sin \left[ \left( { \frac {3417} { c_i} } \right)   \;  \left( \sqrt { \frac {\Delta p} { p_i} } \right) \rightarrow \right]   deg }\)   

Where:

\(\large{ Q_{sv} }\) = steam or vapor flow rate, lb/hr (use to predict flow for perfect or non-perfect gas sizing, for any vapor including steam, at any service condition when fluid density is known)

\(\large{ \rho }\) = density of steam or vapor at inlet, lb/cu ft

\(\large{ p_i }\) = body inlet pressure, psia

\(\large{ C_{vg} }\) = gas sizing flow coefficient

\(\large{ C_i }\) = \(\large{\frac {C_{vg}} {C_{vl}} }\)

\(\large{ \Delta p }\) = pressure differential, psi

 

Steam or Vapor Flow Rate 1000 psig or Less Formula Formula

\(\large{ Q_{sv} = \left[ \left( \frac { C_{vs}\; p_i } {1\;+\;0.00065 \;T_s } \right) \right] \;  sin \left[ \left( { \frac {3417} { c_i} } \right)  \;   \left( \sqrt { \frac {\Delta p} { p_i} } \right) \rightarrow \right]   deg }\)   

Where:

\(\large{ Q_{sv} }\) = steam or vapor flow rate, lb/hr (only to determine steam flow when inlet pressure is 1000 psig or less)

\(\large{ C_{vs} }\) = steam sizing flow coefficient, \(\large{\frac {C_{vg}} {20}}\)

\(\large{ p_i }\) = body inlet pressure, psia

\(\large{ T_s }\) = degrees of superheat, °F

\(\large{ C_i }\) = \(\large{\frac {C_{vg}} {C_{vl}} }\)

\(\large{ \Delta p }\) = pressure differential, psi

 

Tags: Equations for Steam Equations for Valves Equations for Gas Equations for Valve Sizing