Maximum Length of Suction from Tank to Pump?

9/10/2025

We have a facility with an NFPA 13 Extra Hazard 1 sprinkler system.

The client's proposed location of the water storage tank is approximately 33-ft (10m) higher than the level of the protected building and around 100-ft (30m) away.

The client's proposed pump house is closer to the building, separate from the tank.

My question is - is there a maximum length for the suction feed from the tank to the pumphouse under NFPA rules (13, 20, 22)?

I would rather locate the pump house next to the tank and run the delivery main to the building. Thanks in advance.

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8 Comments

Glenn Berger

9/10/2025 08:22:11 am

You need to compare the Net Positive Suction Head Required (NPSHr) vs Net Positive Suction Head Available (NPSHa).

Brian Gerdwagen FPE

9/10/2025 08:25:35 am

If the tank is higher than the pump, the only limit are your calculations.

If the tank is lower than the pump, about 10m is the maximum elevation difference allowed by gravity and water's vapor pressure.

Jesse

9/10/2025 08:25:36 am

Yeah agree with Glenn. You don't want the pump pulling water under a lift condition as you'd limit yourself to a vertical turbine pump.

Ryan Hinson

9/10/2025 09:44:52 am

Perform hydraulic calculations on this section of pipe IAW NFPA 20 (2022) Section 4.16.3 to determine size and allowable length:

- 4.16.3.1 (0 psi where source is elevated) or
- 4.16.3.2 and A.4.16.3.2 (-3 psi where source low water level is at or above the pump centerline).

Joseph Wright

9/10/2025 10:11:20 am

We completed a box store a number of years ago with a remote storage tank approx. 400' from the pump. For a 1500 GPM pump we had to upsize the underground main to 12" instead of 8" to get the suction above -3 psi

Mike Russell

9/10/2025 01:13:09 pm

Joseph is on the right track here. During System Acceptance testing, you need to run the pump at 150% of rated capacity (there is an exception to run at system demand if the water supply is not capable of acheiving the 150%).

If the pump is too far from the tank, you might drop below the minimum -3 psi required at the suction side of the pump during acceptance due to friction loss.

Mark Harris

9/10/2025 11:55:33 am

All good comments. Soundsl like tank outlet wil be above pump so flooded suction and just have to deal withthe hydraulics as noted.

Did have to do this once and we were not the tank or underground provider but had to figure out the vortex plate as the underground supply was bottom not side of tank.

Jack G

9/15/2025 05:51:33 pm

Also depends where the bottom of the tank is.
Yes—- 3 ft of head above the suction line into the pump ( centrifugal) is a must. The line from the tank to the pump shall be hydracually calculated to maintain this. If the tank bottom is below the pump suction, additional capacity ( gallons— height ) must be be added for the proper gallons to flow. ( dead water from tank bottom to top of suction inlet )

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Maximum Length of Suction from Tank to Pump?

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