SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

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.

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 (http://www.wattscanada.ca/pdf/ES-007.pdf), 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 ( http://www.wattscanada.ca/pdf/ES-009.pdf ) 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 http://www.irrigationtutorials.com

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.

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.