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Advanced Member


Wednesday, September 14th 2005, 8:19am

Main Size - System Design

I sent information off to Toro to have them design a system, and I have couple of questions about what they sent back before I proceed.

My property is about 270' long and slopes about 6' from one end to the property to the other. My water meter is at the low end of the property and has a 5/8" meter with a 3/4" copper feed (I asssume) to the house. The house is a good 150' away from the meter and here are the pressures and flows I have. GPM was based on the 5 gallon bucket method, which was using a outside bib which is the first thing tapped in off the supply to the house

Static Water Pressure 57
GPM @ 40psi - 7.1
GMP @ 45psi - 5.5
GMP @ 50psi - 3.5

Full flow without closing valve 10 GPM

Toro said the GPM was too low, and suggested using 1-1/4 main to the valves, and then using 1" to the heads. They designed the system at 50psi & 10 GPM.

So here are my questions

1) Does Toro's overall system design seem right based on this information?

2) What type of backflow preventer should I use, based upon my water meter being at the lowest point on the property? I would say that almost all systems in my area use a Pressure Vacuum breaker. I have posted a question elswhere and it seems as if I can use a Reduced Pressure valve, as it be installed below the highest head.

3) If I use a Pressure Vacuum Breaker will it would hurt system design to run the extra 270' to get the vacuum breaker above the lowest head. There will be zones at the high point, running back down the slope back toward the water meter, as well as zones near the house another 150' away.

4) Since the backflow preventers are certainly more expensive the larger they are, should I come off the water main at 1-1/4 and use a larger backflow or could I use 1" to the backflow preventer and then step up to 1-1/4 after the backflow preventer. I would assume this may matter depending on which type is used.

I would not have so much concern if my property slopes. I know I need a backflow preventor, and I would assume it could effect system design based upon which type I use, and where it gets placed.

Thanks for any input


Supreme Member

Posts: 5,292

Location: Metro NYC


Wednesday, September 14th 2005, 10:41am

Not knowing where you're located, a suggestion about upsizing the house supply to 1-1/4" from the water meter won't be forthcoming. It would be nice to have, but very expensive, if it has to be heavy copper tubing several feet down, to avoid freeze damage. If your meter is near the street, you might tee off right after the meter through a one inch RPZ. Also, you might see if the meter could be swapped for a 3/4" size - although the present meter might be one of the newer ones that have a 3/4" flow in the 5/8" package.

If you do either of those, hold off on design until you re-measure the flow from the new plumbing, to include the losses from the backflow preventer.


Advanced Member


Wednesday, September 14th 2005, 10:54am

I live in Richmond VA, and my plan is to tap into the supply out by the meter, since that is the most convienent place to tap into. I have a 270' X 30' strip of grass that is out by the street (which is where the meter is) about 50' of woods until a reach a grassy area in front of the house, and then another grassy area behind the house.

The slope presents an issue on what type of backflow I use, where it gets located, and what size main is used, which were my main questions.


Supreme Member


Wednesday, September 14th 2005, 11:40am

Why are you assuming a 3/4" feed from the meter?

While I live much farther south (AL) than you, I too assumed that I had your same setup base on what I read on the meter and the fact that I had a 3/4" copper line comming into the basement.

However, when I called the water company, I was informed that my meter was infact a 3/4" meter, and when I dug down to tie into the water main near the meter, I learned that I acctually had a 1" PCV water line from the meter to the house (apparently is changes from 1" PVC to 3/4" copper a few feed outside of the subteranian basement).

As for what size Backflow to use, it doesn't matter what the size of your feeding pipe is, it depends more upon your flow rate. Based on these specs for a Watts 007 double check (, a flow rate of 10gpm can be handled by a 3/4", 1", or 1.25". Even if you use 1.25" pipe, you don't want to use a 007 larger than 1" (because the 1.25" has a greater pressure loss at 10gmp than the 3/4" and 1"). The 3/4" is designed for a maximum flow of 12gpm, so it would work and be a little cheaper. If you ever want a higher flow than 12gpm, you'd have to use the 1" (it's designed for up to 20gpm) but if 10gpm is already pushing it for your system, you might as well use the 3/4" and save a few bucks. However, based on the specs ( ) for Watts 009 RPZs, a 10gpm system will lose the least amount of pressure if you install a 1" or 1.25" RPZ (both will lose about 12psi where as the 3/4" will lose about 14psi). If you are going to use something other than a Watts 007 DC or Watts 009 RPZ, then you will need to find pressure loss charts for those backflow preventers to determine which will provide the least pressure loss for your 10gpm design.

Right now, your biggest issue with the Toro design is that it is NOT designed for an RPZ. You said that you measured your static water pressure at 57psi and that Toro designed for 50psi. That means they have assumed that you are using a PVB or DC (those will have about a 5psi pressure loss covered by the difference of 57psi static and 50psi designed). If you use an RPZ, your only going to have about 45psi AT BEST to supply a system they have designed for 50psi.

If you are going to use an RPZ, I think you are going to need a redesign that either increases the number of zones or increases the pipe sizes to minimize pressure losses from water flow. Now might be a good time for you to read the information available at


Supreme Member


Wednesday, September 14th 2005, 1:21pm

I'd install a 3/4" rpz right after the meter and run 1-1/4" pvc as the mainline. You can then design your zones for 10 gpm.


Supreme Member

Posts: 5,292

Location: Metro NYC


Wednesday, September 14th 2005, 3:12pm

Forget the Toro design. Do yourself a favor and hook up the 3/4" RPZ (or one inch, if the price is right) and retest the flow and pressure at the RPZ outlet. The flow should be greatly increased, but the pressures will be lower. In fact the pressures at higher flows will probably be low enough to make using standard rotor heads unlikely. But get the numbers before you start speculating on further design.

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