What Is "Cv Factor"?｜HISAKA WORKS,LTD. Valve Division

About "Cv factor"?

The Cv value is a specific coefficient indicating the ease at which a fluid can flow. This value increases in inverse proportion to pressure loss, such that a higher value indicates less pressure loss and easier flow of the fluid.

At the time of valve open, volume or weight of fluid passed into the valve is called capacity of valve. it's fixed depends on kind of valve and port size generally.

But even if the same size and same kind of valve, the capacity is different if maker is different. And it is changed by various factors such as the kind of fluid / differential pressure / temperature / viscosity / specific gravity / pressure / port design, dimensions and etc.. And furthermore, even the same size valves has both big pressure loss and small pressure loss also depends on kind of valve. Therefore slection of valve is difficult because it is neccessary to check and consider about many kinds things.

The evaluated these fluid conditions are called coefficient capacity, it can be selected kind of valve and size easily. There are Cv factor, Kv factor and Av factor for coefficient capacity. Cv factor is using generally, it is expressed factor for fluid 60°F that flow into valve by US gal/min. in a situation of special travel and differential pressure 1 lbf/in2.

If differential pressure is same, flow rate is big so that Cv factor is big. And if Cv factor is same, flow rate is big so that differential pressure is big.

Cv factor can be calculated as following formula.

Cv＝Ｑ×√（Ｇ/Δｐ）

Cv Cv factor Ｑ Flow rate [gal/min] Ｇ Specific gravity (For water =1) Δｐ Differential pressure [lbf/in²]

Kv factor is expressed flow rate for 5～40°C water pass the valve by m3/h. in condition of differential pressure is 1bar,

And Cv factor and Kv factor are different unit, but addapted the following.

KvCv

＝8.65×10－10