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jmed999

New Member

1

Tuesday, May 28th 2013, 8:24pm

Finding the GPM of an installed system...

I have a 4 year old house and I'm trying to gather everything I can about the irrigation system so I can make some design adjustments.

I'm trying to determine the GPM. When I do the bucket test under a hose bib I get about 4.5 GPM. I know there's more GPM coming through my zones. I had an idea....

I went to the water meter and turned 1 zone with the most rotors on it. I then timed the water meter to change by 1 cubic foot. This was very easy since the dial read in tenths of a cubic foot. With the one zone on (and no other water in the house) and after converting ft^3 to GPM I got 9.5 GPM. I then decided to turn 2 zones on. Doing the same thing i got 18 GPM.

I have 2 questions....

-Is this a good way to determine the design GPM?

-Would I use 9.5 or 18 GPM for my design GPM? Also, the main line of the sprinkler system is a 1in PVC pipe and I think it's max safe rating is 18 GPM. So what is my design GPM?

Thanks for your help!

Wet_Boots

Supreme Member

Posts: 4,050

Location: Metro NYC

2

Wednesday, May 29th 2013, 5:39am

No part of a sprinkler system will tell you what the water supply is. You look only at the supply plumbing (meter, street pressure)

jmed999

New Member

3

Wednesday, May 29th 2013, 6:05am

No part of a sprinkler system will tell you what the water supply is. You look only at the supply plumbing (meter, street pressure)
Sorry, I'm confused. I was looking at the supply plumbing meter at the street and turning the sprinkler system on. The supply water meter gave me cubic feet which converted to 9.5 GPM with 1 zone on and 18 GPM with 2 zones on.

-Is this a good way to determine the design GPM?

-Would I use 9.5 or 18 GPM for my design GPM? Also, the main line of the sprinkler system is a 1in PVC pipe and I think it's max safe rating is 18 GPM. So what is my design GPM?



Thanks!

Wet_Boots

Supreme Member

Posts: 4,050

Location: Metro NYC

4

Wednesday, May 29th 2013, 7:09am

You measure flow and pressure simultaneously, and create a chart of different flows and the pressures associated with them. The idea isn't to run every possible bit of flow, unless you have a lawn that is acres in size.

Consider the possibility that the system was properly designed in the first place, as regards zone flow rates.

jmed999

New Member

5

Wednesday, May 29th 2013, 7:33am

You measure flow and pressure simultaneously, and create a chart of different flows and the pressures associated with them. The idea isn't to run every possible bit of flow, unless you have a lawn that is acres in size.

Consider the possibility that the system was properly designed in the first place, as regards zone flow rates.


Thanks for the quick reply!

I'm filling out the rain bird design form and it asks for a GPM. So when filling out the form what GPM do I write down? The hose bib GPM of 4.5, the GPM with 1 zone running of 9.5, the GPM of 2 zones running of 18, or the max safe GPM from a chart with 1"PVC which happens to be the same 18GPM?

Also the Toro "Update Design" form does ask for GPM at different pressures. They say to do a 5 gallon bucket test at the hose bib to calc GPM at different pressures. This gives me very low GPMs like in the 4 GPM range. The problem is I know that my GPM with one zone running is 9.5 GPM by looking at the meter and converting ft^3 to GPM. So I'm not sure what to put on the Toro upgrade form....do I use a bucket/hose bib test or the actual GPM from my water meter when running 1 zone?

This post has been edited 4 times, last edit by "jmed999" (May 29th 2013, 7:43am)


6

Tuesday, June 4th 2013, 2:22pm

Meter Size?

I think your best bet is to find the flow chart for your meter. My guess is you have a 5/8 or 3/4 meter. If It is a 3/4 meter and you have around 70 PSI of static pressure your maximum recommended flow will be around 13.5 gpm and your working pressure (in witch you build your design off of) will be around 60 psi.

Now like others have stated the meter can push much more water depending on the pressure, however you never want to design a system using %100 of the meters capacity. If you max out the water supply the will not be able to use any water in your house the same time the sprinklers are on.

Hope this helps.
:)

www.smartearthsprinklers.com





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