Calculate Flow Coefficient Kv of Solenoid Valve

Flow Coefficient Kv

Definition Kv-value: Amount of flow (m3/hour) of water of 20°C in a valve with a pressure loss of 1 bar.

The amount of flow of a fluid through a (solenoid) valve can easily be calculated with flow coefficient Kv. Please note that for gases (e.g. air) a different formula is used (see correction factor gases below).

The Kv-value expresses the flow rate of water in m3/hour in a valve with a pressure loss of 1 bar and a temperature of 20°C. Pay attention that the Kv-value is expressed in m3/hour, while the kv-value (lowercase!) is expressed in l/min.

To calculate the flow rate the following formula is used:

Flow Coefficient Kv

where:

  • Q = flow rate of liquid (m3/hour)
  • Kv = flow coefficient (m3/hour)
  • SG = Specific Gravity (=1 for water)
  • dp = pressure differential over the valve (bar)

The Kv-value of a valve is determined by a standardized test according to VDI/VDE 2173. For this purpose a test set-up is used, such as shown in the following schematic drawing:

Kv-value of a valve is determined

Cv & Kv Relation :

Sometimes, the Cv value is given instead of the Kv value. The Cv value can be converted to the Kv-value with a conversion factor:

  • Cv = 1.16 Kv
  • Kv = 0.853 Cv

The diagram below is a nice tool to simplify the conversion between the different coefficients. The conversion factor between two coefficients is indicated with arrows.

Cv and Kv Relation of Valve

Kv (with a capital K) expresses the flow rate in m3/hour, kv (lowercase) in l/min.

Valves In Parallel:

If several valves are connected in parallel, the Kv value can be determined simply by adding up all Kv values.

Correction Factor For Gases

When using gases, a different formula for the flow rate should be used. Also, a distinction between subsonic and supersonic flows is made. “Qn” indicates that the formula is valid for standard conditions (20°C).

The flow rate is expressed in Nm3/h (Normal cubic metre per hour).

Correction Factor For Gases

Where:

  • dP = pressure loss (bar)
  • Kv = flow coefficient (m3/hour)
  • p1 and p2 are respectively the absolute inlet and outlet pressure (bar)
  • ? = specific gravity at standard conditions (20°C) in kg/m3
  • T = absolute temperature in Kelvin (0K = -273.15°C)

Example

Consider a circuit with a solenoid valve with an inlet pressure (water) of 5 bars. The required flow rate is at least 5 litres per minute. The maximum allowed pressure loss is 1 bar, therefore the outlet pressure is minimally 4 bars. What is the minimum required Kv-value?

minimum required Kv-value

The Kv-value must be at least 0.3.

Also Read: Control Valve Cv Calculation

Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address

1 thought on “Calculate Flow Coefficient Kv of Solenoid Valve”

Leave a Comment

Share via
Follow us and never miss an update!