WHAT IS Cv (Kv) AND HOW IT USED

What is Cv vs. and what is Kv:

-  A Cv Flow Coefficient specifies the volume of water (in US gpm at 60°F/15.55°C) that will flow through a valve with a 1.0 PSI pressure drop across the valve.

     Thus a Cv Flow Coefficient of 10 indicates that a 1.0 PSI pressure drop will occur with a flow of 10 US gpm of water through the valve.

-  A Kv Flow Coefficient specifies the volume of water in m³/hour at 68 °F/20°C that will flow through a valve with a 1.0 bar pressure drop across the valve.

     Thus a Kv Flow Coefficient of 10 indicates that a 1.0 bar pressure drop will occur with a flow of 10m³/hour of water through the valve.

The difference between the two is only the system in which they are calculated, respectively imperial for the Cv and metric for the Kv. Therefore you can convert Kv into Cv and vice-versa using the following formula:   K_v = 0,865 C_v

The Flow Coefficient is normally used to size valves in a plant.  Once flow rate and pressure lost are known, Cv is calculated (or easily found in the technical datasheets) and based on that value, the most appropriate DN valve size can then be identified.  Simply, you need a big enough hole in the ball for media to flow through. If the hole is too small, the pressure will drop.  If the hole is too big, pressure loss will also take place.  Additionally, this means that you have overspent on a larger size valve than was necessary, and you’ve wasted some money (which will not make your boss happy…).

For further clarification or additional information, or to develop special OEM products custom sized to your plant’s pressure specifications, our Engineering department would be pleased to assist.