BSRIA BG29/2021 “Pre-Commission Cleaning of Pipework Systems” (Amended 6th edition) & BSRIA BG 50 “Water Treatment for Closed Heating and Cooling Systems” both recommend the use of  side stream filtration to maintain water quality and keep systems clean for the life if the system.

The water in closed systems usually contains a suspension of fine, abrasive particles which is harmful to the equipment and leads to unscheduled shutdowns and increased maintenance. There are various sources of these particles, mostly resulting from corrosion—oxygen dissolved in the fluid being an important contributor. They are rarely oxygen-free during operation, due to constant air leakage through pressure equalization valves, pipe joints, pump packing, etc. In addition, a quantity of oxygen, although small, is continually added to the system through makeup water. Since most systems are largely constructed of steel, this leads to the generation and circulation of suspended iron oxide particles throughout the equipment. Other sources of particulate matter are millscale and debris left over from assembly, as well as material introduced when the system is opened up for routine maintenance. Following any biocide treatment it can be common to see the release of debris which has been held out by biofilms leading to an increase in suspended solids.

Suspended iron oxide particles and other debris including micro biological proliferation, are very abrasive to mechanical pump seals and can coat or plug up heating coils, causing them to lose their heat-transfer ability. Additionally, areas of the piping and equipment that become covered with debris are subject to under-deposit corrosion and can provide suitable conditions for planktonic conditions to arise which can contribute to MIC (Microbiological induced corrosion)

The purpose of a sidestream filter is to remove or filter out suspended particles from the recirculating water to improve efficiency and protect critical components from damage. Some side stream filters will also provide easy user access to the system to allow the addition of water treatment chemicals either in liquid or solid chemical form.

Side Stream Filtration Systems are generally designed to treat 5 – 15% of the main water circuit flow, to remove both suspended solids and the chemically treated biomass. Our filter media are available in a range of absolute micron ratings so the removal efficiency can be adjusted to achieve a progressive clean up of the re- circulating water. Typically a 20 µm rate filter is used for the initial clean up. Once this is achieved a finer filter can be used e.g.10 µm absolute. We recommend the use of absolute rated filters as unlike nominal filters they maintain their removal efficiency for contaminants throughout the lifetime of the filter, even under varying water quality conditions. It is typical for nominal filters to suffer reduced removal efficiency or to unload previously retained contaminants after a period of use and this will cause unexpected system fouling.

Benefits of installing a ph Water Technologies Side Stream Filtration System


  • Protection of automated valving from fouling to ensure effective building temperature control is maintained
  • Removal of suspended solids to reduce abrasive wear and tear on process plant.
  • Removal of chemically treated biomass to further reduce pipework degradation.
  • Reduced time and lower labour costs when compared to a conventional flushing regime.
  • Reduced maintenance, equipment down time and repair costs.