Although plastic pipe systems are rated at typically 9/10 and 15/16 bar (imperial and metric respectively), many users are unaware of what pressure their system is actually running at. In general, most process, with the exception of high pressure wash jets and some mains water supplies, operate well below 3 or 4 bar. Typically, sand filters and other pieces of equipment run at a 2.5 to 3 bar maximum, whilst cooling, fluid transfer, coarse filtration (above 20 microns) and other systems usually run below 2 bar.

One bar pressure is the equivalent of 10 metres of water head which in turn is the equivalent of about 14.7psi.

Drinking water (in the UK) coming direct from the mains, is usually at between 3 and 6 bar, depending on the location. Care should be taken however, when linking new pipe systems up to the mains, as there are bylaws that prevent the direct connection of mains to closed pipe systems that are used for anything apart from a direct tap. The bylaws insist that there is a "break tank" that will prevent any potential of siphoning back into the main. This is why a cold water cistern is provided, that in turn, supplies the water to heating systems, bath tubs etc. So if you are using a mains water connection to a pond, pool or other process, you must first put it through a break tank, which will, in turn, overcome any high pressure that will be encountered. Any pipework used before the break tank must be WRAS (Water Regulatory Advisory Scheme) approved, and only higher pressure rated systems usually accommodate this. After the break tank, non-WRAS approved, lower pressure, lower cost parts can be used.

In summary, before you assume that you have a high pressure system, take time to check the information plates on pumps and equipment. More often than not, you will find that your system is actually running at a lower pressure than you assumed. This means that you can probably save when buying your plastic pipe and fittings, as you can choose 9 / 10 bar systems rather than 15 / 16 bar ones.