Very high velocity in fire sprinkler pipes

[mech4321]

For a retrofit project with a 40 years old sprinkler system. Would it be acceptable to have branch lines and main pipes at a water velocity of about 110 ft/s. A high rated fire pump would be added, but this would avoid replacing the small diameter piping in the existing tenant spaces. Is there risk of breaking the pipes at this velocity, or blocking the sprinkler system with debris dislodging from the existing pipes?

Hydraulic calculations would not be accurate at this velocity but maybe a safety factor on the sprinkler demand could be added for this?

Thanks
Alex

 

[LittleInch]

Acceptable - I don't think so - this isn't a typo here?? is it one hundred and ten ft/sec / 33m/sec??

There is a risk of lots of things here including forces on tees and elbows, dynamic loads during activation and forces associated with it. Anything on the inside will be ripped off at a velocity like that. As for surge pressures....

The pressure needed must be huge.

Any water system 40 years old must be close to life expired due to spot corrosion issues.

I think if you tried this, you wouldn't need many sprinklers as the system would just leak water everywhere.

It sounds a wholly bad idea based on what you've described.

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

 

[mech4321]

Thanks for your replie

What would be the maximum acceptable velocity from your opinion, in order to avoid replacing too much piping. Piping is in good condition (scedule 40). Ultrasound tests done on the entire piping indicate that the pipe thickness lost is only 8%.

 

[LittleInch]

Around 10 to 15, maybe 20ft/sec max for the odd bit of pipe which isn't used much.

If you search flow velocity or max velocity on this site you'll find a few guides as to what is reasonable /normal range

I suppose fire systems don't flow so oxygen would be used up and not replenished so you probably do have a decent life in it.

Why the sudden increase in flow by what sounds like a factor of 6 or more?

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

 

[mech4321]

NFPA 13 doen't not impose max velocity anymore. FM ask for 30 ft/s in aboveground piping.
The replacement of the existing piping will affect operations in tenant spaces and cost more than a fire pump, so I was looking for a midrange value to reduce de fire pump capacity and replace only a minimum of piping.

This is an old building and hazard classification has changed making the water demand increased. Hydraulic overage factor is also increasing the water demand du to the high pressure required.

 

[Artisi]

My initial thoughts would be what pressure is being imposed on the system, the other concerns would follow after ensuring the pipework was ok.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[EdStainless]

20-30 ft/sec in a fire system doesn't bother me, after all if it is used it is an emergency and not long term service.
Other than the massive increase in pressure that this would take, I would also be concerned about the forces on the piping. Are the hangers and supports ready to handle the large reaction forces from this high of a flow?

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