FILTERS & STRAINERS - FILTERS PDF Print E-mail
Written by Norrie   
Tuesday, 11 May 2010 19:22
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FILTERS & STRAINERS
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1. FILTERS (Figure: 24)

Filters are generally constructed as cylinders containing some type of screening element through which the fluids are forced to flow. The elements are made up of various types of materials depending on the degree of filtration required. Some filter elements consist of special paper which will collect solid particles while allowing the fluid to pass through.

Filters used in process operations to remove solid particles, are constructed of a number of elements made up of wire frames or perforated metal tubes encased by finely woven cloth or metal wires (screens).

Other types contain fibre-glass elements which adsorb the particles of dirt, scale and rust. Still further types consist of 'basket' type elements which can easily be removed, cleaned and replaced. The filter elements are placed in a cylindrical vessel which is connected into the pipe-work carrying the fluid.

In continuous processes, two filter units may be installed, where one is in use while the other is on 'standby'. A total filter bypass is also usually fitted for use should both units become fouled due to excess solids in the system not allowing cleaning or element replacement to take place. However, in such a case, the filters must be re-commissioned as soon as possible.

The system will have a means of measuring the pressure drop across the filter and, when this D.P. reaches a certain point, an alarm switch may be activated. The filters must then be changed over, the dirty filter is then isolated, de-pressured, drained and opened up to remove the dirty elements. New elements are then installed and the unit 'boxed up'.

The clean filter is then refilled and/or re-pressurized by using the small lines and valves provided. While refilling, air is vented to ensure that the filter is liquid/gas full. It is then placed on 'standby'. Where a single filter unit is installed, again, the bypass is used while cleaning is carried out.


Figure: 24