Why Discharge Fire Pump to Water Storage Tank?

12/5/2022

I'm looking at a few projects that have fire pumps and above-ground cylindrical storage tanks for fire protection.

Some projects I have seen have recirculation after the fire pump discharge underground and back into the storage tank. Frustrated I can't find much on this in NFPA 22 or elsewhere.

Is this part of a means for freeze-protection, or to keep the water from getting stagnant, or for pump testing (in which case I guess it would have to branch off from the flow meter)?

Or is it likely engineer preference? Is it a military requirement?

Thanks in advance.

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12 Comments

Dan Wilder

12/5/2022 07:05:18 am

Environment, reliability, and cost savings.

Yes, any ITM discharge not able to be measured via a test header would need a flow meter. Most of the pumps I do have a pump discharge-flow meter-testing manifold (hose header or back to tank) which also allows the flow meter to be calibrated onsite without having to remove it. The flow meter allows testing without water discharge for a couple years as allowed in NFPA 25.

Sprinkler water is considered non-potable and is not allowed to be discharged into storm drains per the Clean Water Act.

It doesn't deplete a water source needed for firefighting efforts for a monthly/quarterly/yearly test..i.e. lowering the available water for use in an event while it works to refill itself.

Also, water costs so putting it back into the reservoir that it came from saves the owner money.

It would not be helpful for freeze protection due to the non-continuous nature of the testing. Stagnant water isn't an issue but there is a water quality aspect to tanks that need to be addressed. Pumps (protecting industrial properties in my experience but can be for any application) pull from ponds without an issue.

Franck

12/5/2022 08:22:14 am

Perfect answer, as usual :)

Jay

12/5/2022 05:52:31 pm

Hi Dan, what do you mean that the Clean Water Act doesn't allow you to discharge sprinkler water into a storm drain? Every main drain test and typical fire pump test (flowing water from the test header) discharges sprinkler water to a storm drain.

Jay

12/5/2022 05:55:46 pm

Please ignore my previous post.
I completely lost my mind there for a second.

Anthony

12/5/2022 08:06:52 am

Dan hit it on the head. I've done several tank supplied systems recently and in areas that have a well provide the 'maintenance fill' and if you're not testing back into the tank you end up needing to call and pay for and coordinate with a water supplier every time you test the system. That is expensive and annoying.

Glenn Berger

12/5/2022 08:10:17 am

On projects that I have a water storage tank, I do recirc the fire pump test header back to the tank. In addition to the reasons that Dan mentions, returning water to the tank prevents flooding and damage to landscaping or others in the way of several thousands of gallon of water flow at a significant pressure.

Jesse

12/5/2022 08:13:02 am

Seems everyone here beat me to it. I always design a re-cirq back to the tank for all the reasons listed above.

Franck

12/5/2022 08:20:57 am

In Europe, where we are not using test headers but test lines with flowmeter, they have always been designed that way. The main reason at that time was to save money. When you flow test your pump every week and up to 150% every year, you can save a lot of money.
In addition there are all the benefits listed above (flood exposure, environmental impact, waste of valuable resource…)

Alex

12/5/2022 08:33:05 am

Hi, seems like everyone hit it on the head. Re-cirq back to the tank for testing purposes.

Anonymous

12/5/2022 11:30:08 am

Thanks all - I guess what I was trying to visualize is that instead of the test loop (though the flow meter) tying back to the immediate suction side of the pump as is typical, I gather it instead routes back to the tank itself,* not both.
*above the water level in the tank

Does NFPA #25 (ed. 2020) 8.3.3.9.2 then allow this method of flowing back to the tank/reservoir to suffice even for the 3rd test, without having to flow hose streams?

Dan Wilder

12/5/2022 02:15:13 pm

You get 2 years of flow meter usage with no water discharge; the third year requires water flow not recirculation.

If setup correctly, the flow meter loop feeds the discharge piping (either a hose header to ground or back to a water source like a pond or tank).

Something similar to the below (not an endorsement for the site, just a useful visual graphic).
https://www.anvil-fire.com/apps_pump_sizing.html

Anonymous

12/5/2022 04:00:53 pm

Gotcha. No way around the test header for the 3rd year, and for the other two, flow meter to tank recirc. (We would typically add a normally-closed valve before the test header hose valves).

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Why Discharge Fire Pump to Water Storage Tank?

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