Strainers are integrated into heating and cooling systems to filter impurities from the circulating medium.
Impurities consist of debris, packing and materials that enter the pipes during operation. Deposits of scale/rust or materials from the medium can become dislodged and subsequently flushed around the system. In district heating systems, deposits/materials can also be introduced from the supply network.
Strainers are located before meters and control valves, to prevent impurities from damaging them or causing them to close. To determine when a filter requires cleaning, a pressure gauge can be mounted on each side of the filter to monitor the pressure drop. Note that district heating system providers often require strainers to be located before the consumption meter, to protect it against deposits/materials from the supply network, but also forbid the installation of pressure gauges near the meter.
Furthermore, isolating valves should also be located as closely as possible on each side of the strainer, to minimise the amount of water that needs to be drained during cleaning.