Why Does a Closed System Need a Filter?

Why Does a Closed System Need a Filter?

How to improve system performance and save money at the same time.

Closed systems circulate the same body of water and are not subject to blowdown and makeup in the way that steam boilers and cooling towers are. The most common closed systems are used for:

Hot water heating of buildings, industry, and institutions

Chilled water systems used for industry cooling and comfort cooling

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, with oxygen dissolved in the water being an important contributor. Closed systems 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.

Suspended iron oxide particles and other debris may be very abrasive to mechanical pump seals or may 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, leading to further damage and release of corrosion by-products.

Implementing and maintaining a properly designed chemical treatment program is the first and most important step towards preventing corrosive oxygen from attacking the metals in the system. However, since it is virtually impossible to prevent the introduction of suspended material, an excellent way the keep the system clean is by the use of a sidestream filter.

A sidestream filter is one which filters a small portion of the total circulation, usually between 5 and 10 %. These units are relatively small and may be obtained in different pore sizes. For most applications a 30 micron filter rating will give excellent results.

The preferred protection combination is a comprehensive chemical treatment program used in conjunction with a sidestream filter. Suspension agents keep particles suspended until the sidestream filter removes them from the water.

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