Description

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.

q/ṁ

Calculate flow rate

Δp

Calculate pressure drop

Cv/Kv

Calculate flow coefficient

Select value to input. You should enter selected one. The other one will be calculated

q

volumetric flow rate

ṁ

mass flow rate

Select value to input. You should enter selected one. The other one will be calculated.

Cv

flow coefficient in imperial units - gpm

Kv

flow coefficient in metric units - m³/h

Select value to input. You should enter selected one. The other one will be calculated.

v

flow velocity

D

internal pipe diameter

When is this calculator suitable?

To select a size of a control valve, you should calculate the required flow coefficient Cv/Kv for the flow rate and pressure drop.

For a specific control valve, flow coefficient Cv/Kv is determined experimentally by control valve manufacturers, and you can found it in manufacturers technical specifications.

They express coefficient Cv/Kv 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: Cv-imperial, Kv-metric]. You can use the calculator to calculate maximum flow rate through control valve for given pressure drop and known flow coefficient of control valve Cv. With maximum flow rate calculated, you can compare control valves from different manufacturers for their efficiency for the same nominal size.

Control valve calculator is suitable for turbulent flow of liquids.

When is this calculator not relevant?

Flashing, cavitation, and chocked flow may reduce the control valve capacity. That calculation is not in this version of control valve calculator.

How is the calculation executed?

The calculator is calculating flow coefficient Cv/Kv 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 Cv/Kv is the proportional constant:

where is:

q - flow rate
Cv - flow coefficient
Δp - pressure drop
S - specific gravity (relative density)