# Valve Sizing for Gas and Steam

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: Steam Gas Valve Sizing