The RPZ valve is a type of double check valve assembly, which means it has two independently operating check valves. The valves are designed to close automatically if there is a drop in pressure on the downstream side of the valve, preventing backflow. The RPZ valve also has a relief valve that opens to allow the release of pressure in the event of a valve failure.

When it comes to servicing RPZ valves, it is recommended to have them serviced at least once a year. During servicing, a certified backflow prevention technician will check the valve for proper operation, test the relief valve, and make any necessary repairs or adjustments. It is important to have RPZ valves serviced regularly to ensure that they are functioning properly and to prevent backflow.

A category 5 air gap is another method of backflow prevention. It is a physical separation between the water supply and the contaminated water, for example, in the event of a failure of a mechanical device or a cross-connection. This type of air gap is typically used in situations where there is a high risk of contamination, such as in healthcare facilities, laboratories, or other places where potable water may come into contact with hazardous chemicals or pollutants.

It is important to have an air gap that is at least twice the diameter of the supply pipe, to ensure that there is a sufficient physical separation between the water supply and the contaminated water. Air gaps do not need servicing as it is a physical barrier.

In summary, a Category 4 Reduced Pressure Zone (RPZ) valve and a category 5 air gap are two different methods of backflow prevention that are used in situations where there is a high risk of contamination. RPZ valves are designed to prevent backflow by creating a pressure differential and should be serviced at least once a year. Category 5 air gap is a physical separation between the water supply and the contaminated water, it does not need servicing.