fire pump critical speed

[saliba11]

hello all,

we have a 20" suction, 16" discharge 5400 gpm fire pump.

Is there any concept like "criticial speed" for suction and discharge lines.?

Does any code indicate a maximum speed not to exceed in these lines.

thanks..

saliba

 

[Artisi]

Do you mean maximum velocity of the flow through the pipeline/s.

Naresuan University
Phitsanulok
Thailand

 

[BigInch]

Your velocity of 1.7 m/s in your 20" is OK. This is about half of the rule of thumb maximum for liquid pipelines. The velocity in your 16" is somewhat high at 2.6 m/s, but still not excessive for a well designed system. Both velocities are reasonable.

There is no code limitation on velocity per say, although the higher velocity you have, the more pressure drop you will experience in the pipe, which leaves less pressure for your outlet flows. There are minimum pressure and minimum flow requirements at your outlets.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com

 

[saliba11]

Thanks biginch.

I guess these are recommended velocities.

what should be the maximum allowable velocity you think.


could we say 3.4 m/s for 20".

 

[BigInch]

For long pipelines we generally hold it to 3 m/s to limit overall pressure drops in the 50 miles or so until the next pump station and to keep some limits on erosion, but it can be increased in shorter pipes, where you usually have more pressure drop to work with. If you have the pressure available and can still make your fire flows at the required outlet pressures, I'd say you could go even as high as 6 or 7 m/s. Erosion will not be a major factor in firewater systems that do not operate on a daily basis, however with those velocities you might experience high surge pressures when flowrates change rapidly on starts, shutdowns and changing flows between monitors. Over 2 m/s surge pressures can sometimes start to be problematic.

Going the Big Inch!

http://virtualpipeline.spaces.msn.com