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I have no clue what an RPZ is. One of the best backflow preventers that I have bought is a Watts PVB (Pressure Vaccum Breaker). They are pretty cheap for backflow preventers. Another Good, Cheap PVB is a febco. Hope this helps.

<b>Let me start by explaining or defining the term backflow so that other readers can benefit from this reply also:</b>

The term Backflow means any unwanted flow of used or non-potable water or substance from any domestic, industrial or institutional piping system into the pure, potable water distribution system. The direction of flow under these conditions is in the reverse direction from that intended by the system and normally assumed by the owner of the system. Backflow may be caused by numerous specific conditions; but, basically the reverse pressure gradient may be due to either a loss of pressure in the supply main called backsiphonage, or by the flow from a customer's pressurized system through an unprotected cross-connection, which is called backpressure. Thus the term backflow covers both a backsiphonage condition and a backpressure condition. A reversal of flow in a distribution main--or in the customer's system--can be created by any change of system pressure wherein the pressure at the supply point becomes lower than the pressure at the point of use. When this happens in an unprotected situation the water at the point of use will be siphoned back into the system; thus, potentially polluting or contaminating the remainder of the customer's system. It is also possible that the contaminated or polluted water could continue to backflow into the public distribution system. The point at which it is possible for a non-potable substance to come in contact with the potable drinking water system is called a cross-connection. To prevent backflow from occurring at the point of a cross-connection a backflow prevention assembly must be installed. However, it is important the backflow prevention assembly match the particular hydraulic conditions at that location and is suitable to protect against the degree of hazard present.
<b>Pollutants:</b> are unwanted substances that can cause bad taste or odor, or are a nuisance.
<b>Contaminants:</b> are unwanted substances that can cause illness or death. Toxic substances.

There are five (5)distinct types of piping or mechanical assemblies which are considered to be backflow prevention assemblies; but, it must be stressed that these are not all equally acceptable as protection against all types of hazards. The degree of hazard must be assessed along with they type of cross-connection present to determine which type of backflow prevention assembly is most suitable to the situation.

<b>The five (5) types of backflow preventers are as follows:</b>

<b>Air Gap:</b> is a physical separation of the supply pipe by at least two pipe diameters (never less than one inch) vertically above the overflow rim of the receiving vessel. In this case line pressure is lost. Therefore, a booster pump is usually needed downstream, unless the flow of the water by gravity is sufficient for the water use. <b>These type is not recommended for use in sprinkler systems.</b>

<b>Atmospheric (non-pressure) Type Vacuum Breaker {AVB}:</b> The AVB is always placed downstream from all shut-off valves. Its air inlet valve closes when the water flows in the normal direction. But, as water ceases to flow the air inlet valve opens, thus interrupting the possible backsiphonage effect. If piping or a hose is attached to this assembly and run to a point of higher elevation, the backpressure will keep the air inlet valve closed because of the pressure created by the elevation of water. <b>Hence, it would not provide the intended protection.</b> Therefore, this type of assembly must always be installed at least six (6) inches above all downstream piping and outlets. Additionally, this assembly may not have shut-off valves or obstructions downstream. A shut-off valve would keep the assembly under pressure and allow the air inlet valve (or float check) to seal against the air inlet port, thus causing the assembly to act as an elbow, not a backflow preventer. The AVB may not be under continuous pressure for this same reason.
<b>This type of protection should not be used to protect from backflow in a sprinkler

<b>Yes, SprinklerWarehouse.com does sell the following types of backflow devices:</b> Pressure Vacuum Breaker {PVB}, Double Check Valve Assembly {DC}, and the Reduced Pressure Principle Assembly {RPZ}.

<b>These types of devices are made by several manufacturers. SprinklerWarehouse.com sells backflow devices from the following manufacturers:</b>
Febco, Watts, Conbraco, and Toro (Toro is not recommended since the plastic degrades rapidly).

<b>Here are the links to see or order the backflow devices:</b>
Febco: http://www.sprinklerwarehouse.com/shop3/BackflowFebco.html
Watts: http://www.sprinklerwarehouse.com/shop3/BackflowWatts.html
Conbraco: http://www.sprinklerwarehouse.com/shop3/BackflowConbraco.html
Toro: http://www.sprinklerwarehouse.com/shop3/BackflowToro.html
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