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

It depends...

If you get a brass regulator, and you have anti-siphon valves rather than a separate backflow preventer, then the regulator should come before the valves.

If you get PVC regulators, the ones I've seen claim that they should not remain under constant pressure. So each valve would need a seprate regulator to be installed AFTER the valves.

Based on what I've learned at irrigationtutorials.com, if the pressure to your irrigation system is 80 PSI or greater, you need a regulator. But if you have an RPZ backflow preventer, you're going to lose about 10 to 15 psi of pressure. So if your system is borderline needing a regulator, having a brass RPZ might be enough to get your pressure below the 80 psi level.

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Oh, one other thing I didn't think of... you can also use a PVC regulator if your system has a master valve. In that case, you can use one PVC regulator between the master valve and the individual circuit valves.

Did the inspector tell you what the pressure is? If not You should first get an accurate pressure reading before installing a Pressure Reducing Valve ( PRV ) . I recommend to call up your local water district and ask what your normal pressure on the street is. You can also buy a pressure guage at your local HD and hook it up to your hose bib NEXT to your main house shut off. However It's a 50/50 shot if the hose bib is prior to the House shut off / and or prior to the house PRV. So your guessing at best by this way.

Just install it just prior to your Main Shut off to the irrigation system. Hopefully your Anti-siphon valve is a back flow assembly. This is the easier way to test the pressure by using the test cocks of the backflow assembly. Care to share a picture?

Don't skimp on quality-
Use nothing less then a then a brass PRV. I Recommend the bullet proof 1" Wilkins Zurn Pressure Reducing Valve . You can shop around for a better price of course and your local HD/ Lowes should have these

Also , I agree with Hookoo regarding the RPZ.

If you only have a Anti-siphon valve then I recommend to take the sucker out and replace it with Reduced Pressure Back Flow Assembly . This should act as the main shut off to your irrigation system as well as provide ample back flow protection.

I agree that you should first test to see what your static water pressure is. Buy a pressure gauge at the hardware store that you can fasten to your hose bib. This will tell you the maximum water pressure your irrigation parts will see. "Most" irrigation components are rated upwards of 80psi. Pipes (poly-100psi max::VC-120 to 160psi max). Valves and fittings are rated upwards of 120psi. Residential sprinkler heads are rated at operating pressures of 70-80psi max. Operating pressure is lower than static pressure, so keep that in mind.

We've installed numerous systems with 100psi+ static pressures. The one thing to be careful of is to insure that water flow does NOT exceed appropriate velocities. With higher pressures, the likelihood of damage caused by excessive flow is much higher, but can be avoided.