Max. velocity on yard mains.

[DavidCR]

We´d like to know what is the maximum recomended design flow speed in pipes (and minimum speed if there is one), of a yard system (private) which feeds foam systems, monitors, hidrants on a thermal plant. It is fed by centrifugal horizontal pumps.

We met the diameters required by NFPA 20 on discharge lines and I know there are speeds that must be obtained to flush the pipes (3m/s), we have diameters from 6" to 12".

The plant may grow, and we want to consider the possibiliy of buying more pumps in the future and to know if the pipes can widstand more flow.

Thanks.

 

[nomad42]

Since you say the plant is likely to grow, I would limit the initial velocity of flow to 10 ft/sec. (max). Be sure to check the resulting pressure drop against the available head of your pumps. Be sure you have enough motor hp. You may even set it lower (5 -8 ft/sec), depending on the existing pumps.

 

[TravisMack]

There is currently NOTHING in NFPA 13 or 24 that mandates a maximum velocity. If you are feeding foam-water fire sprinkler risers, there is a minimum flow rate required through the proportioners to generate the correct foam-water concentration.

The limit on your piping will simply be the amount of water you can to the system at a given pressure.

I have seen jurisdications with velocity limits on yard mains ranging from 10 - 15 ft/sec. However, there is nothing in NFPA 13 or 24 that sets a maximum velocity.

 

[gouveia]

mfpd is correct. The only reference I am aware of that has a velocity would be in NFPA 20. Don't have a copy handy, but I believe it references the velocity of an underground supplying the suction side of a fire pump. Since you already have a pump supplying the system this would not apply.

 

[TravisMack]

The value you are referring to is for 10 pipe diameters upstream of the suction flange on a fire pump. The velocity in that section of pipe can not exceed 15 ft/sec.

 

[DTR]

The above question is one I have come across many times!! and as our friends above say there are no guidelines within any of the NFPA Codes regarding velocities through pipes. There is however a requirement within BS5306 Part 2 (British Standard for Fire Extinguishing Systems) that I always use which is a maximum of 10m/sec through a pipe and 6m/sec through a valve.