In order to design valves for a process system correctly, the valve size is determined by the required flow rate. The Kv-value serves as a calculation basis for the different process conditions. This value is stated in the following table with regard to nominal diameter and standards.
Kv-Value
The Kv-value is a parameter defining the flow rate of valves. It describes the amount of water from 5° to 30°C which flows through the valve at a pressure loss of 1 bar.
The Kvs-value describes the Kv-value when the valve is 100% open.
For Water 5-30 °C applies:
General Liquid Flow Formula:
Conversion:
For the correct Kv to Cv conversion calculation, use only the stated units formulas below. The Kv-value must be converted from (cubic meter / hour) by utilizing the following conversion factors. In the US the flow rate of water is measured with the Cv-value in US-gallons per minute (gpm) with a pressure drop of Δp 1 PSI.
Conversion of Kv to Cv Cv = 1,17 x Kv Conversion of Cv to Kv Kv = 0,86 x Cv
Explanations:
Kv in m³/h = flow rate parameter Q in m³/h = volume flow rate ρ in kg/m³ = specific gravity p1 in bar = pressure before the valve p2 in bar = pressure after the valve Δp in bar = pressure drop through the valve Δp = p1 – p2
The Kvs-Values in the table refer to the specification with two-way valves with EPDM diaphragm (Depending on the specification variations are possible).
