# Kv and Cv values

L

#### Lejo

Metric and imperial units apply for Kv and Cv values respectively. But what is the definition of both? How are Kv and/or Cv related to
pressure and flow of a medium? And to each other, if so? (I prefer to work in the metric system.)

S

#### Scott Hayes

"The Cv is defined as the flow through the valve in U.S. gallons per minute of water at at 60 F with a pressure drop across the valve of one psi."

Scott Hayes

S

#### Sengupta, Subhro

Kv is defined as flow in cubic meters per hour of water (temp 5 to 40 deg C)passing through the valve when pressure drop is 1 bar across the valve.

Cv is defined as flow in US gpm of water (temp 60 deg F)passing through the valve when pressure drop is 1 psi across the valve.
They are related as Cv = 1.156*Kv.
The simplest formula for CV (in metric) for liquid, Cv=1.156*Q*sqrt(G/DP), where Q is flow in m3/hr,DP is in bar and G is Sp. gravity.

M

#### Mr. C. B. Indi

Kv and Cv value are flow coefficient of control valve. They indicate the flow capacity of control valve. Their defination is as follows -

Kv value- It is defined as the flow of water at 20 deg. C. in cubic meter per hour when differential pressure across the control valve is 1 bar.

Cv value- It is defined as flow of water at 70 deg. F. in USGPM when differential pressure across the control valve is 1 psi.

Conversion of Kv and Cv
1 Cv = 1.17 Kv.

E

#### editor

A practical use for CV would be as follows:
The coefficient CV is used by engineers to size valves . In layman's terms you need a big enough hole for liquid to go through. If the whole is too small you can get pressure drops that make your liquid drop below its vapour pressure. If your liquid drops below its vapour pressure you will get implosions that damage the valve trims.

M

#### mgh

> Kv is defined as flow in cubic meters per hour of water (temp 5 to 40 deg C)passing through the valve when
> pressure drop is 1 bar across the valve.

> Cv is defined as flow in US gpm of water (temp 60 deg F)passing through the valve when pressure drop is 1 psi across
> the valve. They are related as Cv = 1.156*Kv.

> The simplest formula for CV (in metric) for liquid,
> Cv=1.156*Q*sqrt(G/DP),
> where Q is flow in m3/hr,DP is in bar and G is Sp. gravity.

if DP is in bar, then unit of kv will be m3/hr-sqrt(bar).
as G has no unit.

Please explain, i'm not getting it.