A reduced pressure zone device (RPZD) is used to protect water from unwanted contamination. Also known as backflow preventers, these devices can be grouped into three categories, including method, device and assembly. They provide practical ways to prevent backflow from occurring.
Backflow assemblies typically come with two resilient seated isolation or shut off valves. The components also feature test ports that are well-positioned. The assemblies can be serviced in-line as well as repaired and tested without the need to detach any parts. On the other hand, only certified testers are allowed to troubleshoot the devices.
However, up to 15 backflow-related devices cannot undergo testing due to the lack of test ports or isolation valves. In addition, there are no standardized test procedures that are specifically designed for the device. This aspect differentiates an assembly and a device. The former is testable.
As with the devices, a barometric loop or air gap cannot be tested. These variants are used to counteract any backflow.
Features
A reduced pressure zone device is well suited for use in hazardous applications. This includes applications that have the potential of causing considerable harm if backflow were to occur. However, this does not include risks associated with human waste contamination. The units come with redundant design that helps prevent back siphonage and back pressure.
They have the capacity to provide reliable protection even when the check valves are damaged. In these cases, the units are tested to ensure correct operation. The RPZD is generally preferred over an air gap due to the smaller size of the head across the device.
The unit features two independent check valves that are plumbed in series. The configuration also incorporates a pressure monitored chamber that is located between the two components. The water supply pressure is higher than the pressure in the chamber.
A differential pressure relief valve is responsible for maintaining the chamber’s pressure level. The valve relieves any excess pressure from the chamber by discharging it via a drain. Inspectors verify correct operation of the valve using four test cocks. The verification process is carried out using a differential pressure meter.
Two RPZDs are required at facilities that handle constant pressure. The devices are installed parallel to each other. This is aimed at ensuring that at least one device is operational when the other is undergoing tests or repairs. When the relief device is faulty, it leaks past shutoff seats. Brief episodes of discharge can be caused by normal water use
When the upstream valve is passing, the flow will head in one direction owing to the differential pressure. As a result, the pressure buildup will be relieved via the drain.
