The type of check valve used has a great bearing on the pressure transients that can occur in a system. European designers have long recognised this and the use of nozzle type check valves is more common place. In the scheme of things the use of this type of valve is but a small investment in reducing risk and fatigue damage.
Swing check valves are considered by many as unsuitable in high head systems.
Simple clapper valves tend to have a very poor response, spring assisted split disc valves, especially with stronger springs, are a little better, whereas nozzle type valves generally have a an excellent response.
Many facilities exposed to check valve slam with conventional swing check valves have been made silent by the use of the nozzle type check valve. For more details refer www.noreva.de
The nozzle check comes in two types. The single spindle single spring or annulus multiple spring type. Like all items of equipment the designer should take note of the specific design requirements of the equipment. The valve should be installed in a pipeline in accordance with the manufacturer’s instructions and the knowledge available from recognised piping and valve design texts.
There have been some instances of horizontal orientated single spring nozzle type valves jamming and users should check with the particular manufacturer as to their experiences. A rare problem with the multiple spring design is that it may jam when a flow is unevenly distributed, for example after a bend. Some models are better than others and the engineer needs to determine this in the technical evaluation.
Jamming of a valve has to do with internal friction of a valve and the applied spring strength, not whether they are multiple spring of not. Noreva check valves are optimised to allow the highest spring strength possible, providing an improved dynamic behaviour but also this will prevent jamming of the valve. Further more the Noreva designs have less friction of moving parts than other designs again eliminating the chance of jamming. The Noreva designs are less prone to failure than other designs on the market. They have replaced many of their competitor’s valves, especially in critical applications.
Noreva is considered by many, including their competitors, as technology leaders. These manufacturers provide technical information based on flow testing at Delft laboratories. They have characteristics of low pressure loss and non slam action.
The surge analysis needs information such as the pressure to re open a closed valve, the reverse velocity to close. The latter can be obtained only if the manufacturer has tested the valve. Facilities exist at the Delft Laboratories or Utah State University to test independently. Many manufacturers have not had their valves tested, they rely upon a design copied or licensed from decades previously and the current resources just do not understand the fundamental design of the devices and how they interact with the piping system.
Technically professional valve suppliers, such as Noreva, can provide deceleration versus maximum reverse velocity data.
There may be other valve suppliers with similarly competent valves and technology and the designer should investigate these fully before deploying there valves. Readers are referred to the work by Prof ARD Thorley for a more complete understanding of the behaviour of check valves and their relationship to transient events.
Difficult applications such as sewage and slurries require specific designs of valves and sometimes compromises in their design and application. In fact automated isolation valves may replace a check valve in severe applications such as these. The characterised Cv versus % open combined with opening/closing time of these valves then needs to be considered in the analysis. Fluid Transients in Pipeline Systems Prof ARD
Comparison of Check Valve