What is the primary difference between a double check valve and a reduced pressure zone device?

The primary difference between a double check valve and a reduced pressure zone (RPZ) device lies in their ability to prevent back siphonage. A double check valve is designed to prevent backflow in low-hazard situations, primarily protecting against backpressure; however, it does not provide protection against back siphonage, which can occur when the pressure in a system drops significantly, creating a vacuum that pulls water back into the system.

In contrast, the reduced pressure zone device is specifically engineered to prevent both backpressure and back siphonage, thus providing a higher level of protection for the potable water supply. The RPZ device includes an additional pressure differential assembly that ensures that the pressure within the protected area remains significantly lower than the pressure of the incoming water, thereby safeguarding against any potential backflow situations, including those caused by siphoning.

This difference in functionality is critical when determining the appropriate backflow prevention device for various applications, especially in scenarios where contamination of the drinking water supply is a significant concern.