Self-cleaning filters

The use of sidestream sand filters or self-cleaning filters may be advantageous in reducing the level of suspended solids to help maintain clean waterside surfaces. If the size of the cooling system and the extent of the problem justifies it, blending with better quality water supplies or treatment of part of the makeup water volume by reverse osmosis (RO) may prove economically viable. 

Cooling water makeup should contain less than 5 ppm SS. If the level of suspended solids is considerably higher, say over 20 ppm SS, pretreatment by the use of polyelectrolytes or filtration is recommended. If the SS level is perhaps 5 to 10 ppm or if there is air-blown dust entering a cooling system, a sidestream sand filter or self-cleaning filter will be of benefit. In cases of high SS, chemical polymeric dispersants may be suitable as a total replacement for the sidestream filter but preferably will be used in tandem with a filter. 

However, for routine problems such as excess dust and dirt ingress into HVAC and similar types of cooling systems, which can normally be shut down for a few hours during a weekend, these self-cleaning filters may present a simple and economic solution to the problem. 

A typical design of an automatic self-cleaning filter allows pressurized dirty water to first enter an upper chamber via a flanged entry port, where the water is filtered through a coarse screen. From here the water is then directed through a stainless steel fine mesh screen located in a lower chamber and out through a flanged exit port. 

Most analyzer sampling systems require a filter with at least one wire mesh strainer (100 mesh or finer) to remove larger particles that might cause plugging. Available filter materials include cellulose, which should only be considered if it does not absorb the components of interest. Sintered metallic filters can remove particles as fine as 2 ym, cellulose filters can remove down to 3 /on, and ceramic or porous metallic elements can trap particles of 13 ym or larger. When the solids content is high, two filters can be installed in parallel with isolation valves on each. Motorized self-cleaning filters are also available for such services. 

Windsor. Berks SL4 IRD Tel +44(0)1628 440906 Fax +44 (0) 1628 475667 Email info oxfordfiltration.com Web wAW.oxfordfiltration.com Manufacturer and Supplier of Simplex. Duplex Strainers and Self Clean filters for virtually any fluid duty... 

In simple clean pellet storage applications, a plain clam shell-type vent is adequate to allow air in and out of the tank. In very dusty or powder applications, either bag-type or continuous self-cleaning filters may be required. 

Sawyer, H. T., Dynamic self-cleaning filter for liquids , US Patent No. 4158 629, June 19 (1979)... 

Depending on the plant layout, storage facilities are available for intermediate storage and for finished product storage. Products will be filtered to specification using self cleaning filters and/or disposable cartridge and bag filters. 

A very different type of self-cleaning filter is the Fibrotex element, developed by Kalsep, illustrated in Figure 3.60. The element is a bunch of fibres, which acts as a... 

It is recommended that a filter screen be used ahead of and in conjunction with filters of this type. Continuous self-cleaning filters of this kind are considered to be one of the most reliable types of bulk water filter available, with low plant costs and high clarification efficiencies. A full scale array of moving bed filters is shown in Figure 4.6. 

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