Gas control valve calculator

calculation of flow coefficient - Cg or Kg

online since 2007

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Calculation setup
Flow rates and velocity
Fluid properties

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q - volumetric flow rate
Fluid flow rate in terms of units of volume per unit of time
ṁ - mass flow rate
Fluid flow rate in terms of units of mass per unit of time
V - velocity
Flow velocity in terms of units of distance per unit of time
D - internal diameter
Internal circular pipe diameter
Cv - flow coefficient
In imperial units - gpm
Kv - flow coefficient
In metric units - m3/h
p - pressure
Fluid pressure at the start of the pipe for gas density calculation based on the ideal gas state equation
ρ - fluid density
Mass per unit of volume

Calculation setup

Select value to calculate. You should enter not selected one.
Calculate flow rate
Calculate pressure drop
Calculate flow coefficient
Select value to input. You should enter selected one. The other one will be calculated
volumetric flow rate
mass flow rate
Select value to input. You should enter selected one. The other one will be calculated.
flow coefficient in imperial units - gpm
flow coefficient in metric units - m3/h
Select value to input. You should enter selected one. The other one will be calculated.
flow velocity
internal pipe diameter

When is this calculator suitable?

To select a size of a gas control valve, you should calculate the required flow coefficient Cg or Kg for the given flow rate and pressure drop.

For a specific gas control valve, the flow coefficient Cg or Kg is determined experimentally by control valve manufacturers, and you can found it in manufacturers technical specifications. They express flow coefficient Cg or Kg as the flow rate of water in g.p.m. [m3/h] for a pressure drop of 1 psi [1 bar] across a flow passage [flow coefficient: Cg-imperial, Kg-metric].

You can calculate the gas control valve capacity for given upstream and downstream pressure and known flow coefficient Cg or Kg.

With maximum flow rate calculated, you can compare capacities of control valves from different manufacturers with the same nominal size.

Standard EN334 is covering gas control valves and pressure regulators for pressures up to 100 bar. The calculator is in line with the same standard.

When is this calculator not relevant?

You should use a flow coefficient calculator for an incompressible flow of liquids.

How is the calculation executed?

The calculator is calculating flow coefficient Cg or Kg using the relationship between pressure drop and flow rate in the control valve which is for complete turbulent flow following power law where flow coefficient is the proportional constant:

where is:

q - flow rate
Cg - flow coefficient
Δp - pressure drop

Available in download version

save/open multiple results
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custom fluid properties
K factor for fittings, resistance coefficient
pipe surface roughness selection
select between gauge and absolute pressure
compressible isothermal flow
dry air isothermal flow
gas offtake flow
natural gas flow


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