Paul Millard, Technical Manager at the Water Regulations Advisory Scheme (WRAS), explains reduced pressure zone valves, and why they’re so important.

A reduced pressure zone (RPZ) valve is the common name given to a Type BA device, which is the only mechanical backflow prevention arrangement capable of providing protection up to Fluid Category 4. 

This category includes substances which can cause significant harm to health, including chemicals that are toxic, carcinogenic, or pesticides, and it is therefore vital that appropriate backflow protection is used when working with these types of water supplies.

The RPZ valve works by ensuring that the water entering the downstream system is at a lower pressure than the incoming supply, typically reducing it by 0.7-1bar, using a combination of check valves and a relief valve to monitor and maintain the lower pressure. 

An RPZ valve can often be one of the safest backflow prevention devices available, providing the correct upkeep is undertaken. These valves need to be installed by competent and qualified plumbers, tested at least annually, and fully maintained to ensure that they perform correctly and continuously safeguard the water supply. 

Incorrect installation or use can risk contamination and incur costs to put things right, and testing is vital to proper performance. However, these routine tests come at a cost, making the valves expensive to maintain when compared to alternatives such as air gap options. 

The installation or alteration of RPZ valves must be notified to the local water supplier and adhere to the Water Industry Approved Installation Method (AIM 08-01), which has recently been updated and can be found on the WRAS website. It is important that the installation is completed by a fully qualified contractor.

After the initial installation, an RPZ valve will require annual formal commissioning and testing. This requires a test kit to be attached to the test cocks to make sure the valve is operating correctly, and can only be completed by an accredited RPZ tester. Water companies publish a list of approved RPZ testers on the WRAS website.

Good installation is key to ensuring ease of access for regular testing and maintenance. For example, an RPZ installed 2m above ground or too close to other objects means that test equipment cannot be connected to it, so testing can’t be carried out easily. 

One of the most common problems when using RPZ valves is the possibility of pressure fluctuations within the plumbing system. When the fluctuations are excessive, they can cause the relief valve to discharge. Measures may be needed to reduce this as not only is it an unnecessary waste of water, but it can prevent the valve from working correctly. 

Paying attention to the product you are handling, and its correct usage, is absolutely vital when working with water systems. It is important that you are aware of the rules set out in the Water Industry AIM 08-01 and by the Water Supply (Water Fittings) Regulations and Scottish Byelaws when planning any plumbing work. When properly installed and well-maintained, an RPZ valve should work effectively for a long time.