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

You do eliminate the need for isolation check valves upstream of a pump if you put the RPZ upstream of the pump. You also complicate matters, because the RPZ is intended to go outdoors. That places the pump outdoors as well. And since the house plumbing is upstream of the pump, there will be little if any pressure in the house when the sprinklers are on.

No increase in pressure after the Water Department visit? You'd be boosting pressure for the entire house, if you bought one of those package deals, and even the smallest one is capable of creating the negative supply line pressure you want to avoid. Their drawings are missing the suction-side check valve(s) you need to isolate the higher house pressure from the street.

Any pump with a flow capability that subtantially exceeds your measured flow, as you gave in the first post, will be capable of creating that negative pressure you want to avoid. I've observed this phenomenon before, when a sprinklers-only booster pump created negative pressure in the house plumbing. Open a sink faucet, and you hear it sucking air instead of seeing it deliver water. If the pump is set up as a whole-house booster, the negative pressure can still exist in the supply line between the street and your home.

Any problem can be solved by throwing enough money at it. A new water connection, with at least one-inch copper. A pro could go the extra yard to select a special-order booster pump that wouldn't create any negative pressure. But then again, the pro is going to get at least five thousand dollars for installing a sprinkler system on a lot your size.

Nothing like having a prestige zip code to raise the cost of living. It can be that you're expected to hire a service guy to change lightbulbs. Your particular situation is uncommon enough that manufacturers have largely ignored it. One low-pressure-capable sprinkler head has been discontinued. Even a few towns may not be paying enough attention to the negative-pressure phenomenon, if the pressure boosting systems in some new construction I've seen were an indication.