Engineer's Plumbing Blog

Reduced Pressure Zone RPZ valves are backflow preventer devices to protect portable drinking water in the mains supply from contamination in applications such as industrial processes, restaurants, swimming pools and irrigation. Compared to a DCV, the RPZ features an additional differential release valve in the center of the valve body. In cases of a check valve mechanical failure or debris caught inside, the differential release valve opens to cut off the contaminated water source to the portable water mains supply.  The RPZ employs two in-line, independent check valves, captured springs and replaceable check seats with an intermediate relief valve. These features...

Double check valve DCV backflow preventers are designed to protect portable drinking water in the mains supplies from cross-connections in low risk water applications only, where no hazardous chemicals are present. A RPZ reduced pressure zone valve backflow preventer must be used instead in all other situations, when a DCV is regarded as insufficient protections by plumbing authorities. The RPZ design differs from a DCV by featuring an additional differential release valve as a mechanical fail-safe device. The differential release valve opens and dumps contaminated water to isolate from the mains water supply, if one or two of the check...

The solar hot water frost protection valve FPV relies on a mechanical wax filled piston mechanism to operate. The heat in summer from the solar collectors or accumulated debris over time can damage this mechanism, causing the FPV to fail and leak. A dead leg extension fitting can be employed to extend the service life span of the FPV in the filed. 

Australian BSP (British Standard Pitch) thread sizes for plumbing valves and fittings are only nominal and not the physical measurement for the thread diameter. This article explains BSP vs the physical actual thread measurements.