I have an atmospheric vacuum breaker on the feed from my meter to my lawn irrigation system. I am going to install a water-powered backup sump pump in the basement. (This uses city water pressure to drive a secondary sump pump if the primary electric one fails). Code requires an RPZ on the line feeding this secondary sump pump.
Can the new RPZ feed my irrigation system also, and if so, can I eliminate the existing vacuum breaker? The existing AVB is outdoors and about two feet above ground level. The RPZ will be in the basement, about 6 feet below ground level. I live in New Jersey.
In other words, does a below-grade RPZ serving multiple appliances including an irrigation system make the dedicated above-grade AVB unnecessary?
Some background for the uninitiated and curious
AVB (Atmospheric Vacuum Breaker) and RPZ (Reduced Pressure Zone) are two kinds of devices to prevent dirty water from flowing backwards into clean sources. An AVB is relatively low cost, relatively unreliable, and has to be located higher than all the "dirty water" so for a sprinkler system it has to be above ground and above the highest sprinkler head. In many jurisdictions it is regarded as good enough for sprinklers. An RPZ is relatively expensive and requires annual testing and maintenance. It is used where city water flows into known contaminated water. It can be located lower than the dirty water, i.e. it can handle pressure from both directions as long as the clean water is at higher pressure.
The water-driven sump pump uses city water to drive a vacuum pump that sucks water out of the sump pit, where the two flows are mixed and sent outside. Because the pump is actually drawing dirty sump water it is required in almost all jurisdictions to have an RPZ behind it. The RPZ is regarded as superior, meets the higher standard, leading to my question.
Note that for even dirtier water, e.g. actual sewage or poison, no kind of backflow preventer is allowed. You need an air gap, you cannot have a device with one pipe connected to city water and another pipe immersed in sewage.