A reduced pressure zone device is tested with a device called a differential gauge. This gauge uses hoses attached to the various test cocks of the RPZD and checks to be certain that the check valve springs as well as the relief valve spring are not fouled and are working properly. There is a variety of manufacturers of these gauges, but most utilize either a three-valve or a five-valve design to test the RPZD in different ways.

TMVs are often more expensive to install, however, can be repaired and maintained lasting longer on average than a tempering valve. The Australian Standard states that tempering valve testing should be carried out every 12 months with thermostats and o-rings replaced every 5 years.

RPZ Backflow preventerdiagram

In the case of the downstream check valve passing, the differential pressure relief valve prevents the possibility of the chamber pressure from exceeding the supply pressure.

RPZ backflow preventerdetail

The problem with keeping your storage hot water at this temperature is that at 60℃ hot water can cause severe scalding in only a few seconds. Small children, the elderly, and the infirm are some of the groups at most risk of burns.

There are approximately fifteen devices related to backflow which cannot be tested, as they do not have isolation valves or test ports and there are no standards (test procedures) set in place to test for any device. This is what sets an assembly apart from a device. An assembly is testable, but a device is not.

An example of where backflow would harm the water supply is the use of well washing devices inside underground sewerage pumping stations. At times untreated sewerage may contain a variety of harmful gases that will effectively break down and deteriorate concrete wells, hence well washers are utilised to spray water and wash down contaminated concrete walls of a well. All well washers are installed with RPZ Devices in case a pumping station breaks down, and the sewerage level rises above the well washer, causing backflow down the water supply line.

Solution - install a tempering valve or TMV to the hot water pipe supplying personal hygiene areas (bathrooms), in some situations the whole house, which reduces the water to a much safer 50℃ (122℉), or in some cases 45℃ (113℉), to safeguard residents.

Facilities that require constant water pressure must install two RPZDs in parallel so that one device will be available to supply the facility while the other is tested or repaired.

The large volume of water which spends most of the day just sitting in your hot water tank (unless you have instant) is a perfect breeding ground for all sorts of nasty bacteria. One of which is the Legionella bacteria that can cause a serious pneumonia-like bacterial infection Legionnaires disease, which in some cases leads to death.

RPZ backflow preventerfor irrigation system

Tempering valves are usually installed in standard home water heating situations. A thermostatic mixing valve would be fitted if there was a requirement for more exacting control of the water temperature, as well as in larger applications.

Both valves contain a temperature-sensitive element which expands or contracts in response to temperature changes in the incoming water. This expansion and contraction control a slide valve which allows more or less hot or cold water into the mix to consistently maintain the desired temperature.

In the UK,[6] Illinois, New York,[7] Texas,[8] and Missouri(RsMO 10c60-11), the RPZD valve must be tested at least every 12 months by an accredited tester.

RPZ Backflow Preventerprice

RPZ backflow preventertest

It is theoretically possible that, when both valves are faulty, backflow could occur, should the reverse flow rate exceed the capacity of the relief valve.

rpz backflow preventer3/4

A reduced pressure zone device (RPZD, RPZ, or RPZ valve) is a type of backflow prevention device used to protect water supplies from contamination. RPZDs may also be known as reduced pressure principle (RP), reduced pressure principle backflow prevention devices,[1][2] reduced pressure zone assemblies (RPZA),[3] or reduced pressure principle assembly (RPPA).[4]

Prohibiting the growth of bacteria in your hot water system is achieved by maintaining the thermostat at 60℃ (140℉) or above. However, increasing the temperate significantly above this will just result in higher power bills, not added protection.

It’s especially important to fit a solar hot water system with a tempering valve because of the higher temperatures the water can be heated to on hot sunny days.

Because certain combinations of check valve failure and/or system backpressure cause the relief valve to discharge, the device must be mounted in a location where the drain will not become flooded.

A tempering valve is accurate to around 3℃ +/-, while a thermostatic mixing valve can keep the water to 1℃ +/- and responds faster than a tempering valve to changes in incoming water temperature.

RPZ backflow preventerinstallation

A RPZD is considered suitable for significant hazard applications,[note 1] that is, where the consequence of backflow into the water supply would cause significant harm, although not for the highest risks, such as human waste.[5] They are considered suitable because they prevent both back pressure and back-siphonage, because of a redundant design (even with two check valves broken the device still provides protection), and because they are testable to verify correct operation.

Not sure which one is right for your hot water system? Contact our Sutherland Shire plumbers for professional advice and tempering valve installation services.

Australian plumbing regulations state that all hot water systems in new homes must be fitted with a tempering valve to control the hot water supply to the bathrooms. Our plumbers recommend installing a valve on all storage hot water systems, new and old.

Backflow preventers are categorized into three groupings: Assembly, Device or Method. With the exception of elimination, these are the only ways one can control backflow from taking place.

The device consists of two independent check valves, plumbed in series, with a pressure monitored chamber between (also known as the zone). The chamber is maintained at a pressure that is lower than the water supply pressure, but high enough to be useful downstream. The reduced pressure is guaranteed by a differential pressure relief valve, which automatically relieves excess pressure in the chamber by discharging to a drain. Four test cocks are installed to allow an inspector to verify proper operation of the valve with a differential pressure meter. Two valves (one before and one after the RPZD) are provided to allow for testing and repair.

A large tourist attraction in Melbourne was totally shut down due to a Legionnaires disease outbreak caused by bacteria breeding in the building’s air conditioner cooling tower system. This is just one example of many and is why we should take the risk seriously in our homes.

Often tempering valves and TMVs can also restrict the supply of hot water totally if for some reason the cold water stops, further safeguarding against burns.

RPZ backflow preventervs double-check valve

Not sure if you need to install a tempering valve or a thermostatic mixing valve? Your local plumber can provide you with advice specific to your water heating requirements but here’s the low down to get you started.

Discharge from the relief device is an indication that either of the two check valves is 'passing' (leaking past their shutoff seats) or the relief valve itself is faulty. Some normal water use conditions may cause short episodes of discharge (this is why check one has a minimum passing value of relief +3. It is designed to handle the pressure fluctuations).

In the case of the upstream check valve passing, the differential pressure (higher supply pressure compared with the lower chamber pressure) causes any flow to occur only in one direction. A buildup of pressure in the chamber in such a case would be relieved to the drain.

The eight named backflow assemblies all have two resilient seated isolation/shut off valves with properly located test ports. These assemblies have the distinct advantage of being in-line serviceable and can be tested & repaired without having to remove an installed assembly. Special accredited courses are given to test & repair backflow assemblies and only certified testers may test backflow assemblies.