Spring loaded or counterweighted check valves can close before flow reversal. It
depends upon the strength of the springs and size of the counterweight. Its just
a balance of forces thing.
General practice though is that the spring stiffness or counterweights are sized to close quickly but not so to create such a pressure drop as to impact on energy costs.
Noreva non slam check valves are designed to close in <0.4secs. The mass of the moving parts is low and this is how this type of valve achieves a reduction in waterhammer positive pressures as it does. www.noreva.de.
The dynamic characteristics of a check valve should be provided by the manufacturer so that this information can be used in a surge analysis.
If you want a very fast closing valve actuated valves using nitrogen fom a gas bottle has been used on gas and liquid lines in the past.
Geoff
Erik Scheir <erik.scheir@pandora.be> wrote:
As far as I know there are no check valves who closes before flow reverse. An ideal check valve would close at zero flow (working like a diode).
But ideal does no exist, so check valves always closes at return flow. The fast a check valve closes, the best it is with respect to waterhammer.
If you know such check valves please let me know the type and the manufacturer.
Erik.
Van: <a href="/group/PipingDesign/post?postID=bUkaNx7pH8SiMJAMuY5t8T7k7kVUt2Il3ma1ogKHifCoExmOB8hMAJ_1a4IOF5908KgwlrthSmlwa8H68R1-2KdB24A">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=bUkaNx7pH8SiMJAMuY5t8T7k7kVUt2Il3ma1ogKHifCoExmOB8hMAJ_1a4IOF5908KgwlrthSmlwa8H68R1-2KdB24A">PipingDesign@yahoogroups.com</a>]
Namens r_ravoori
Verzonden: Saturday, November 26, 2005 4:54 PM
Aan: <a href="/group/PipingDesign/post?postID=bUkaNx7pH8SiMJAMuY5t8T7k7kVUt2Il3ma1ogKHifCoExmOB8hMAJ_1a4IOF5908KgwlrthSmlwa8H68R1-2KdB24A">PipingDesign@yahoogroups.com</a>
Onderwerp: [PipingDesign] purpose of check valve
Apart from back-flow prevention, there are other uses:
1) Spring loaded or 'silent' check valves assist in minimizing water
hammer effects by the fast closure of the valve before flow reverses.
2) There are other specialized check valves used in steam extraction
lines from turbines. These are power-assisted and prevent water from
entering the turbine.
R.V.Ramachandran
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[Non-text portions of this message have been removed] Received on Wed Nov 30 16:49:00 2005
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