Maximum velocity of water and foam mixture in pipes

[Vijay93]

HI,´

I am currently trying to hydraulically dimension pipes. I would like to know what is the maximum velocity to be used to determine the pipe sizes. 1 pipe has only water and the other has water and foam mixture (3% AFFF Foam). The application is Fire fighting.

Thank you for your help in advance.

 

[hacksaw]

What size nozzles are being used?

The acceptible flows depend on the hose or piping being used.

For liquids 3 m/s (10 ft/s) is commonly a maximum pipe velocity, depending on the fluid, etc.

 

[LittleInch]

If you look on this site you will find many posts.
There is no mandated "maximum".

3m/sec is a commonly used guide figure as a good balance between smaller pipe and higher pressure.

a lot depend son distance as well. Longer pipes - lower velocity is better, shorter ones you could have up to 5 or 7 quite easily and it makes only a few bar difference, but a smaller pipe.

If this is a fire system - see what NFPA say. They regulate everything to the nth degree. I think they give pipe sizes for certain max water flows.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[hateMech]

I don't know about NFPA, but in Europe, EN 12845 for automatic sprinklers does give a limit of 10 m/s in pipes and 6m/s through valves, flow meters and strainers.

 

[Vijay93]

Thank you all for your answers. I believe NFPA does not set a limit to maximum velocity but as mentioned EN 12845 sets the limit to 10m/s in pipes and 6m/s through valves, flow meters and strainers as mentioned by @HateMech

 

[EdStainless]

At some high flow the pressure drop may impact the foaming action.
Typically dP is the limit for flow in FP systems since use if so infrequent.
I believe that NFPA has flow limits for some devices, but as I recall they agree (nearly) with the EN values.

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P.E. Metallurgy