The sizing of a valve is absolutely crucial. It not only affects how much flow can pass through the valve, but it also dictates the flow coefficient and the overall performance.

Here are six key reasons why it’s so important to have a correctly sized valve…

  • Quieter operation
  • More accurate flow control
  • Last longer
  • Won’t leak
  • Inconvenient
  • Expensive

Ensuring that the correct valve size is specified for an application, is essential.

What happens with an undersized valve?

If a valve is too small for a given application, there won’t be enough flow through the valve. The system has to overcompensate by raising the head pressure of the pump. This in turn gives a higher differential pressure across your valve.

Upon leaving the valve there will be a sudden drop in pressure and this will cause it to flash and bubble (otherwise called cavitation). This will significantly reduce the life of the valve as the flashing of liquid creates vibration and turbulence which erodes the seats and seals.

What’s more, cavitation weakens the joints causing the piping to leak and the vibration sound can be carried throughout the whole system.

What’s wrong with an oversized valve?

Whereas with an undersized valve many damages can arise to the system, this isn’t quite to the same effect for an oversized valve. However, it too is just as damaging in terms of controllability.

This becomes a massive issue, especially if you’re using a modulating control valve. To achieve the required flow change, it may need more compelling position changes.

Likewise, the valve and actuator can wear out prematurely as a result of the valve hunting and overshooting continually.

But don’t forget about the CV calculation…

And last but not least, it’s extremely important that the CV calculation is done accurately as it this is wrong, it will affect all of the above.

Visit the Burkert website to do your own valve sizing calculation, thereby ensuring that you have the correct valve to install.

Benefits of using the Burkert sizing programme:

  • Easy access – no installation or registration necessary
  • Calculation of flow coefficient Kv or Cv, flow or pressure drop for media from a large media database
  • Easy sizing for steam with stored steam tables
  • Transparency also for different measurement units through integrated conversion
  • Fast and direct request for quotations
  • For control valves
  • Calculation of the characteristic curves with up to 3 operating points
  • Reliability assessment of valves for operating conditions
  • Warning for critical operating conditions such as cavitation, choking and flashing
  • Includes noise prediction

Based on the flow coefficient Kv/Cv a suitable valve can be selected easily for the operation conditions of your application.

For control valves it is additionally possible to evaluate whether critical conditions restrict the reliability of valves.

Within the process valve selection and sizing tool you can find an info tour with help texts guiding you through the procedure.


Andre Nel

Burkert South Africa (Pty) Ltd
Tel. +27 11 574 6000



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