Industrial Fire Hydrants

This may require mostly local research in order to comply with the relevant codes and agencies:

Fire, plumbing, mechanical codes.

NFPA, FM, UL, ISO (Insurance Services Office), local FD among possible agencies.

As a wild guess (no more than that) an 8-inch pipe at 15 ft/s flow = 2350 gpm. The pump supplies a pipe going in two directions, hence 4700 gpm pump flow, at the hydrant pressure required by the various codes plus pressure losses in the piping.

Etc....

Thanks for Reply We have to comply NFPA Codes, I am checking NFPA 14- and NFPA 24 ,It did not say about how many hydrants in operation ?

I haven't studied this very much, so please don't rely on anything without verification.

Some of what I have run across calls for 20 psig at hydrants. I think this is based on a pumper truck being hooked to the hydrant, and boosting the hose pressure to get a long enough stream. Just guessing, but if the mode of usage is that the hydrants will feed hoses without pressure boost, their pressure--and pump pressure--would need to be higher.

There are also distance criteria spelling out how far hydrants can be from possible fires, and spacing between hydrants.

Local fire officials are likely to become involved with this in any event, and they should be a prime source of information.

What is the intent for the hydrants? Are they a water source for fire hoses directly connected to the hydrant? Or are they a watersource for the fire dept pumper truck?

How many fire hose streams need to be supplied by the system? How many fire truck need to be supported by the ring? What is the value of the property or product being protected by the system?

The answer to these questions will provide key information for pressure and flow rate of the fire pump to be installed.

My semi-scientific wild arsed guess (SWAG) is 2000-3000 gpm at 150 PSI. I would be curious how close the real number comes to my "estimate".

Start by having a flow test performed on the hydrant located the farthest from the input to the ring. It must be known what the "dynamic" pressure is. From there you will be able to size a pump, if one is even required. Pump size will be determined by the total flow required and at what pressure. Ultimately, this is determined by the local AHJ (Authority Having Jurisdiction). This person may be a Fire Marshal, Fire Department Chief, Plant Engineer, basically whoever is in the hot seat for fire activity.

Fire pump size will depend not only on the hydrants but sprinkler system also. Do you have a sprinkler system or only hydrants.

1. If there is a sprinkler system, typical industry prctaice is to size the pump to cater to largest sprinkler demand and add on another 500gpm for the hydrant flow (NFPA 13/14). The storage needs to cater this flow requirements for a min. 120 min period.

2. If there are no sprinklers, then size the pump for maximum no of hydarnts that are expected to operate. In this part of the world, they take 10 LPS flow per hydrant with 2 to 4 hydrants in operation depending on the buiding classification.

3. Also note that fire pumps come in standard sizes, like 1000 gpm, 1500 gpm etc. Given that some one has already sized the ring main size of 8", my guess is the fire pump will be in the vicinity of 2000 gpm give and take.

Hope that helps.

Your guesstimate is close to my guesstimate. I give you a good answer.

Ultimately, the AHJ (authority having jurisdiction) will review, rule, and tell you what size pump he(she) will want for the system.