# How to figure gallons per minute?



## unioncreek (Jun 18, 2002)

Is there a way to figure gallons per minute if you know the pipe size and psi?

Example: 

3/4 inch galvanized pipe
85+ psi

Thanks,
Bob


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## Cabin Fever (May 10, 2002)

How long of pipe and made of what material? (friction loss)

85 psi at inlet or at outlet? (head loss)


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## Wis Bang (Feb 20, 2009)

Stopwatch & 5 gal pail. Divide total time to fill the pail by 5 = GPM.


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## ace admirer (Oct 5, 2005)

usually its pipe size and speed. but if you use an orifice plate and an upstream pressure gauge and a down stream pressure gauge, there are standard orifice plate tables that will get you close to flowrates....i haven't used the tables since i got released from college several decades ago. i now have an ultrasonic doppler unit that you just clamp a transmitter and a receiver to the outside of the pipe to measure speed and it calculated flowrates.......but i quess not everyone has one of those.....

seems there was a method of putting a pressure gauge in the inside radius of an elbow to get a differential pressure for flow rates. 

just using the pressure, pipe size and friction loss will get you within perhaps 20 %,,,wasn't there a thread a few months back on this?


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## cfabe (Feb 27, 2005)

Wis Bang said:


> Stopwatch & 5 gal pail. Divide total time to fill the pail by 5 = GPM.


Actually you need to do it the other way round. Take the 5gals and divide it by the number of minutes it took to fill the bucket. So if it took 45 seconds, you would take 5gal / 0.75min = 6.66gpm


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## unioncreek (Jun 18, 2002)

I figured you'd need more info. We bought a old brick commercial building in town and will be putting a restaurant on the ground floor. There are apartments upstairs the we want to remodel and my son will live in one and we'll rent out the other. The must have a sprinkler system in them to use them as an apartment. I've got an appointment on Monday with the fire protection guy to do and evaluation and estimate. 

Thanks,
Bob


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## deaconjim (Oct 31, 2005)

Here are some tables that might help:

http://www.tpub.com/content/construction/14259/css/14259_50.htm


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## cfabe (Feb 27, 2005)

If that 3/4" is your water main and you're asking to find out if you need to upgrade it... my guess would be that it needs to be over 1" main for a restaurant and sprinklers.


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## SteveO (Apr 14, 2009)

Afternoon,
I hope you aleady have a Spk system in the eatery because you are talking big $$$. A fire feed needs to be 4inch or larger depending on the sf of the building. If you make the upstairs habitable you will need a second egress and a one hour ceiling in the eatery plus a zoned fire alarm.
The added use of a Apt on your service is easy to cure start back at the meter and increase the size of your main to say 1 1/4 for ten feet and tap into it there. There should be no noticable change in the flow to the eatery.
I would visit the building Dept and talk in general terms about what they will make you do or let you do.

enjoy
Steve


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