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Friday, August 13th 2010, 1:19pm

Need help calculating my GPM

Hi all,

I am designing my first sprinkler system and need help calculating my GPM.

Water Meter: 5/8 in
Service Line from WM: 1 in

We have a spigot next to our water on/off lever in the basement and I put a pressure gauge on it and got a reading of about 80 PSI.

The city said to plan/design to 42 PSI.

What should I plan on for a working pressure and for my GPM? I'm getting different answers from different sources/charts.



Supreme Member


Friday, August 13th 2010, 11:51pm

Determining actual GPM is a bit of an itterative process because to get accurate information, you have to estimate what your working pressure at the spray head is going to be, then use charts for the spray head to determine GPM. Add up all the GPMs running through all the pipes, determine pressure losses in the pipes. Use the pressure losses to determine working pressure. Use working pressure to estimate GPM at each spray head. Use GPM of each spray head to determine GPM through each pipe, use GPM through each pipe to determine pressure losses in each pipe, use pressure losses to estimate working pressure at each spray head...

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