Used to control flow and to shut off the water supply so that equipment can be removed for maintenance without draining the whole system, for example it is essential that all pumps have ball valves on the inlet and outlet. Also always use the next size up as, for example, a 32mm ball valve will have a 25mm diameter through the centre therefore use a 40mm ball valve which will have 32mm through it, though using this method will require the use of reducers PLEASE NOTE all our pipe is fully fish safe and has been used by us for many years, all joints are glue fittings using standard 'solvent weld' glue available from us or most DIY shops. All our pipework is metric and directly compatible with all European pipe such as VDL, it is also directly compatible with Aqua Medic Deltec Surchan and almost all European equipment. It will not fit directly onto most U.K. sourced pipework without a metric to imperial adaptor. If you are in any doubt please contact us for advice.