With this data you can compare valves with each other

To assess the flow capacity (output) of a valve, objective comparison values are required. The flow of a valve depends on several factors, such as:

• Flow cross-sectional area
• Absolute inlet pressure
• Absolute outlet pressure
• Pressure drop across the valve
• Temperature
• Medium
• Relative ratios

For proper comparison or calculation, all values must be specified in the same way. For this purpose, the unit normal litre is used: Nl or Ndm³. This represents one litre of air at 0 °C at atmospheric (ambient) pressure.

kv value

The measurement is performed with water and indicates the number of litres of water per minute flowing through the valve at a pressure drop of 1 bar.

Unit: Ndm³/min

• kv × 0.07 = Cv
• kv × 1.259 = S
• kv × 68.65 = Qn
• kv × 0.06 = Kv

Kv value

As above, but expressed in SI units: Nm³/h.

• Kv × 16.67 = kv

Cv factor

The measurement is performed with water and indicates the number of US gallons per minute at a temperature of 15.6 °C (60 °F) and a pressure drop of 0.07 bar (1 PSI).

Notation: US gallons/min.

• Cv × 981.5 = Qn
• Cv × 0.829 = f
• Cv × 14.3 = kv
• Cv × 8.18 = S

f factor

Equivalent to the Cv factor but expressed in imperial US gallons/min.

• f × 1.206 = Cv

S equivalent diameter

Here, the valve (resistance, output) is compared with a measuring orifice of equal flow capacity.

Unit: mm²

• S × 54.53 = Qn
• S × 0.055 = Cv
• S × 0.794 = kv

Qn normal flow capacity

This indicates the output of a valve at a supply pressure of 6 bar and a pressure drop of 1 bar. Since the boundary conditions are not always clearly defined, the comparison is not always entirely precise.

Unit: Nl/min

• Qn × 0.001 = Cv
• Qn × 0.015 = kv
• Qn × 0.018 = S