Engineer's Plumbing Blog

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.