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New Member


Wednesday, September 1st 2010, 2:41pm

New Design Assumptions

I have a well pump on my property and a pressure switch (on 40 PSI off 60 PSI).

I have tested my static pressure to be 48 PSI using my outyside spigot (on 1/2 copper pipe).

I do not know my current GPM , but based on 1" inlet pipe, am guessing about 15 GPM.

I am at the planning stage for my irrigation system (0.92 total acre).

I plan on having my plumber install my backflow preventer and then I will install the system myself.

Short of knowing my working pressure and my GPM, I want to make the following assumptions:

Design for 40 PSI pressure and 13 GPM using 1" PVC pipe

Change my pressure switch on from 40 to 50 and off from 60 to 65

Use the flow control on my valves to regulate the pressure to 40 PSI.

I have 4 areas and 10 zones in my design.

The average GPM is 9 in the other 8 zones (never exceeding 10).

I have 2 other zones where the GPM is over 16.5 and 16 - I need to combine these into 3 zones


Active Member

Posts: 42

Location: east coast


Wednesday, September 1st 2010, 7:39pm

Designing a sprinkler system off of a well supply vs city water is very different. Making assumptions on how much water you can run can get you in trouble. I'll give you some things that you need to verify before you begin any installation.

1. Is the well itself capable of supporting a sprinkler system that may run for 3-4 hrs. a day?
2. What size , HP, is the existing pump and what is its GPM rating. You can not run 13 GPM if the pump is rated at 5 GPM.
3. What is the static level of the well, and what is the expected drawdown of that level under continuous running of the
sprinkler system. These are things that are best answered by the well driller or pump installer if they are available.
4. "static pressure" in a pump/well system is ambiguous as you are dealing with a pressure switch setting of say 40-60 and
you would want your pump to hum along at say 50 -55 psi so as to keep it from cycling.
5. Many residential homes have wells/pumps that are sized to only provide water for general household use. A sprinkler
can have a much higher water demand.

It would be beneficial to you to check these things out prior to doing any type of install. I have seen instances where systems
were installed without checking these things out and found out too late that the sprinkler performance was not what it should be
and/or they actually ran out of water!


Supreme Member

Posts: 5,294

Location: Metro NYC


Thursday, September 2nd 2010, 4:36pm

Make the tie-in first and then measure what is produced - that way you assume nothing. Then you can design your system.


New Member


Tuesday, September 7th 2010, 11:07am


Thanks for all of your advice.

I am working with a local specialist with lots of sprinkler installation experience in the area.

He has done a few plumbing upgrade for me already.

He did say the pumps used in the area are generally 1 HP and I should expect aboyt 13 GPM and be lucky to get 15 GPM.

My plan was to have the backflow installed and then test for the actual GPM.

He did tell me about raising the pressure settings on the pressure switch.

As far as the othe questions concerning the well, I moved in the house about 2 years ago and may be able to locate the company that set up the well and ask question. In the area, most of the homes (well over 90%) do have a sprinkler system install and are using well as well.

The only expense I did not anticipate is iron in the water that potentially will turn the sidewalk, white vinyl fence and the side of the house a "redish" color. My local expert is already looking for a system for me. He did mention a dual tank solution that switches off/on to backwash and keep up with demand etc. That sounds expensive. He will test the water today and let me know what the iron level is. Currently, I have a low PH issue that is beng managed by soda ash. We know that because the sink, tub and toilet turn a bluish color if not treated. But there's no visual evidence of any iron issue from the well.

So far, my irrigation plan call for 15 zones, with 7 zones on the iron treated backflow and the other 8 zones on the 2nd backflow (not being reated for iron). This will be used in the back of the house where there's no potential staining issues. Because I did not anticipate any iron issues, there's no monies allocated for that (yet). So the plan is to install the 2 backflows anyway and connect them to the main line. We will provide aifrastructure to split these in the spring (1 using the well water directly and the other being treate/filtered for iron when more monies become available.


New Member


Tuesday, September 7th 2010, 11:11am

Make the tie-in first and then measure what is produced - that way you assume nothing. Then you can design your system.


Thanks for this suggestion.

My plan was to have the backflow installed and then test for GPM and pressure.
The design specification is all done.

All I need to do is to verify GPM and pressure.

I am meeting with the local expert today to go over details.

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