Pressure reducing valves are needed for a number of reasons in the home. Be it a tap that splashes everywhere when fully open or a hot water system tank that requires a certain pressure to work safely. Even some water softeners require pressure reducing valves to prevent their overflow from constantly running.

They come in 15mm and 22mm compression.

Where do I install a pressure reducing valve?
In the mains cold water feed before the component that requires reduced pressure. You can even fit a pressure reducing valve directly after the mains water stop cock to allow control over the whole premises pressure

How do I install a pressure reducing valve?
These valves are very easy to install. Isolate the water supply and cut the pipe where you want to install the valve. Using an adjustable spanner and some grips, tighten the compression fittings on either side of the valve. Wrap some PTFE around the thread of the valve gauge and wind it into the main valve body. On top of the valve is a screwdriver slot. According to the direction arrows, rotate the screw to achieve the desired pressure.