RPZ Sizing and Location

Its a type of backflow preventer guys.

In this case I believe it stands for Reduced Pressure Zone - which gives an indication of how it works to prevent a backflow of water.

The purpose of a backflow preventer is to protect potable water supplies. If the upstream pressure from the municipality were to drop, a back siphoning effect could cause water flow in the opposite direction, back into the municipal supply. If say there was a garden hose attached to a hose bib and that hose was sitting in a pool of stagnant water and the valve to the hose was open, a back siphoning would pull contaminated water from the stagnant pool back into the municipal supply and contaminate it. This could lead to sickness or worse for all of the other customers connected to that same municipal supply. An RPZ backflow preventer senses the reverse flow of water and shunts the water flow to drain, thereby protecting the upstream municipal supply of potable water.

Backflow Preventer is a generic term. There are different methods to prevent back flow (e.g. vacuum breakers, double check valves, air gaps, RPZ) but the RPZ method is the most reliable and is usually what is required by municipalities on multi-family dwellings, businesses and manufacturing facilities. Single family dwellings usually do not have RPZs but employ the use of vacuum breakers or air gaps. Lavatory fixtures usually have some type of vacuum breaker or air gap integrated into their design.

In your situation, perhaps there is some type of air gap that protects the municipal supply. Does your building have a water tower and if so, is there a separation between where the outlet pipe from the municipal supply and the overflow level of the water storage tank? If not, you are most likely in violation of the code and could be subject to severe penalties. You may still be in violation of code even with an air gap. Air gaps are an arcane method of backflow prevention and do not provide the level of protection that typically comes from an RPZ. I'm not a code expert and you need to review the local codes and ordinances to see what applies in your situation.

One word of advice, if you are going to take the time to install an ZPZ, install two of them in parallel and make sure that you have valves on the inlet and outlet sides of both of them. The reason, if an RPZ fails inspection, the inspector is required to take the device out of service. By having two, you will reduce the chance of a water outage to your building. Another important thing, backflow prevention devices must be registered with the municipality to which the water supply is connected and they are required to be teseted at least once per year.

I hope this helps.

Regards,

Paul

I would stay full pipe size with a 2" RPZ (reduced pressure zone) backflow preventer. This comes as an assembly with valve body, inlet and outlet service valves, strainer, and test petcocks. The whole assembly costs about $650 for a standard flow version and $950 for a high flow version. It is about 2 feet long as I recall. [?]

It should be installed after the water meter and before any branches to the building water system. There is a drain on this valve, so it would be handy if the building has a floor drain nearby.

If you Google "backflow preventer" you can probably find some pictures.