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How to Calculate a Fire Pump Test Header Size?

2/15/2023

8 Comments

 
NFPA 20 says that if the test header supply main is more than 15 feet from the fire pump, it must be increased one pipe size or hydraulically calculated based on 150 percent of the rated pump capacity.

What form does the hydraulic calculation take?

Are we trying to determine if the main can flow 150 percent of the pump rating without running out of pressure?

How low a pressure would be acceptable?

Is this a one time calculation to size the main or is this a calculation that must be performed during each annual fire pump test?

Thanks in advance.

​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Sent in anonymously for discussion. Click Title to View | Submit Your Question | Subscribe
8 Comments
Dan
2/15/2023 07:11:30 am

The appendix in the 22' Ed [A4.22.3.4(3)] has a worksheet for this scenario. As the calculation is based off a number (the pump rating) x a % of the capacity of the pump, one calculation is all that is required, and the test must meet this minimum. I've never done this before either...

That final number minus the pump discharge pressure (as the calculation is ran all the way back to the discharge flange of the pump) is your required pump discharge...if the pump discharge is higher than calculations then the pipe sizing and testing configuration (including number of hoses and length of hoses) is acceptable.

I would then suggest making a placard for this testing method, so future ITM companies perform the same test configuration and don't write up the pump as deficient because they tested with 3 hoses instead of 4 and used 100' hoses vs 50' and the couldn't get pitot pressures to work.

Reply
Jesse
2/15/2023 08:06:21 am

Dan's last comment about making up a placard is an excellent idea. I never thought about how helpful this would be.

Reply
Franck
2/15/2023 08:24:13 am

It is always good to give explanations for future reference. That avoids a lot of questions and misunderstanding.

Just like the provision of hydraulic system nameplates at base of each risers with detailed information on the sprinkler systems (design, hydraulic claculation results). This saves a lot of time for any further evaluation of the systems.

Anthony
2/15/2023 03:55:52 pm

I agree with the others, Dan has this down.

Glenn Berger
2/15/2023 08:46:37 am

I like the placard suggestion made by Dan above. This would be in addition to additional required documentation that is required to be provided.

As far as the question -- "how low pressure would a pressure be acceptable?" I would recommend following NFPA 291 Paragraph 4.6.6 for acceptable minimum (10 psi) in measuring flow with a pitot gauge.

Reply
Mike Morey
2/15/2023 09:07:03 am

I made a spreadsheet for this based on the annex form, whenever we run into one of these I have our guys run it and then put a note on the drawing that sizing is not increased per hydraulic calculation with a safety pressure of X. Ironically I've always said do the calculation because I've literally never had one fail, until a few months ago when i finally found a pump that it didn't work and we did have to do the up-size. That was a very small/low pressure vertical inline.

Reply
Kamran Khalid
3/28/2023 03:07:39 am

Can i also get the spreadsheet. I also need it for a project. You can email me. My email is kamranqa@hotmail.com

Reply
Richard H
2/16/2023 11:38:34 am

Mike, Any chance I could get a copy of your spread sheet? I'm still struggling here. Thank you sir.

Reply



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  • Blog
  • Forum
  • THE TOOLKIT
    • SUBMIT AN IDEA
    • BACKFLOW DATABASE*
    • CLEAN AGENT ESTIMATOR*
    • CLOUD CEILING CALCULATOR
    • DOMESTIC DEMAND*
    • FIRE FLOW CALCULATOR*
    • FIRE PUMP ANALYZER*
    • FIRE PUMP DATABASE*
    • FRICTION LOSS CALCULATOR
    • HANGER SPACER*
    • IBC TRANSLATOR*
    • K-FACTOR SELECTOR*
    • NFPA 13 EDITION TRANSLATOR ('19 ONLY)
    • NFPA 13 EDITION TRANSLATOR ('99-'22)*
    • LIQUIDS ANALYZER*
    • OBSTRUCTION CALCULATOR
    • OBSTRUCTIONS AGAINST WALL*
    • PLUMBING FIXTURE COUNTS
    • QUICK RESPONSE AREA REDUCTION
    • REMOTE AREA ANALYZER*
    • SPRINKLER DATABASE*
    • SPRINKLER FLOW*
    • SYSTEM ESTIMATOR*
    • TEST & DRAIN CALCULATOR
    • THRUST BLOCK CALCULATOR
    • TRAPEZE CALCULATOR
    • UNIT CONVERTER
    • VOLUME & COMPRESSOR CALCULATOR
    • WATER STORAGE*
    • WATER SUPPLY (US)
    • WATER SUPPLY (METRIC)
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