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Starting Member

Posts: 1

Location: USA


Friday, July 21st 2006, 11:43am

Water Pressure and GPM - Again

I have read the 2 year old posting in regards to water pressure and GPM and while it made sense, I am still having doubts in my design.

The pipe entering my home is 1", my water meter is 3/4", and the pipe after the meter that is servicing my home is 1". I get show 60 PSI from the facet outside the house with a 1/2" pipe connecting this to the 1" pipe servicing the rest of my home. My hose bibe is so low to the ground it's difficult to get a GPM reading. Also, from the many sources of literature I've read, the water presssure and GPM diminish from the resistance of the polypipe running out to the sprinkler heads.

I originally design my system by using a chart that lets you look up the pipe and water meter size and gives you the GPM. In my case that is 11-13 GPM. I have 10 Hunter PGJ rotor meters using a total of 13 GPM (1.3 x 10 GPM) in one zone. My neighbors, who had their systems professionally installed, have 3-4 rotors on a zone. I show 10 rotors.

Do I know what the PSI or GPM will be 100 feet from the valve box? What am I missing?

Also would you design to spray into/over an 8ft pine tree or up to it?


Senior Member

Posts: 15

Location: USA


Saturday, July 22nd 2006, 8:57pm

Based on the facts you have provided, design your system to use approximately 10 gpm. Now you have a cushion in the event that you have miscalculated, or that water usage in your area increases and your system will be able to still perform well with a higher water demand being placed on the municipal water system as a whole. Play it safe when designing your system. Always leave yourself a cushion. Also, why would you want to spray over a pine tree? It is just going to keep growing .


Supreme Member


Monday, July 24th 2006, 7:14am

<i>Do I know what the PSI or GPM will be 100 feet from the valve box? What am I missing?</i>

You have to look up Friction Loss Tables. These tables tell you how much pressure is lost through every 100' of pipe for a given pipe size and gpm.

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