Can Fire Pump Suction Use a 45-Degree Elbow?

9/4/2024

To comply with NFPA-20, the fire pump suction must have at least 10 pipe diameters from the pump flange to the elbow or tee. According to Section 4.16.6.3, the pipe can be horizontal or vertical.

Does the vertical pipe have to be at a 90-degree angle, or will a 45-degree angle be acceptable because that's the only way it can be installed?

Thanks in advance.

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6 Comments

Anthony

9/4/2024 07:27:49 am

I don't think a plain reading of the code would allow for that. It's an either-or situation. Maybe get sign off from the manufacture? I believe the issue is cavitation from turbulent flow so if they sign off you might get an AHJ to buy it.

Dan Wilder

9/4/2024 08:22:28 am

Would really be better with a picture of the proposed install and this assumes a horizontal split case pump

The supply piping PARALLEL to the drive shaft of the pump is the 10 diameter straight pipe application. If the supply pipe needs a 45 or other angled variation, no issue as long as there is the 10 pipe diameters of straight pipe (PERPENDICULAR to the drive shaft and measured from the face of the pump suction). Now this does not apply to piping coming in vertically (from above or below) but if an offset (elbow with a 90°, 45°, 22½°, or 11¼° turn) is added to move the pipe centerline in the horizontal axis parallel to the drive shaft within 10 pipe diameters, that is an issue.

Make the offset as high as possible, allowing the 10 pipe diameter requirement to be met, and not at the pump and this should remedy the situation. If it's coming from below, time to get creative with either moving the pump or getting the UG installer to move the final flange location.

Glenn Berger

9/4/2024 08:46:09 am

I am in agreement with Dan. Need to see where this 45 ell is proposed.

Jesse

9/4/2024 10:26:44 am

I'm trying to visualize what's being proposed and having a tough time.

Pete H

9/4/2024 11:52:23 am

Dan nailed this better than I ever could.

That said, this sounds like an issue of what you can do as opposed to what you want to do.

You may want to consult your local AHJ and see if he's up for a site visit before the pump installation.

Jack G

9/4/2024 12:18:12 pm

I also agree with Dan.
90 degree elbows are a source of cavitation , and the 10 elbows are required to straighten the flow.
As the position of the 45 is not known, I would say that a 45 with 2-3 feet to another 45 might be like a long radius elbow and might be ok. Consult the manufacturer.
I can’t say I ve ever did this .

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Can Fire Pump Suction Use a 45-Degree Elbow?

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