Cartridge-type filtration-units

The use of in-line filters between injectors and colunm can prevent the accumulation of particulate material on the inlet frit of an analytical column, and can avoid back-pressure problems. A second, and often overlooked, site for filter installation is between the column and the detector. Cartridge-type filtration-units that contain readily changed, 0.2-/i,m filters are commercially available, and they contribute insignificantly to peak broadening. These filters are essential for the prevention of clogged detectors when laboratory-packed columns are used. 

The most common types of filters used in industrial processing are pressure filters such filter presses, leaf filters, and cartridge filters, as well as vacuum filters like the rotary drum vacuum filter, and the rotary vacuum disc filter. Most filtration units produce a cake, which at long cycles may become reasonably dry at the expense of declining the flow rafes. Keeping consfanf... 

Dry smoke particles may be collected by impinganent filtration, using pad, bag, pocket or cartridge types of filter, with paper or synthetic media, as well as in electrostatic and electrodynamic separators. Very high efficiencies may be obtained by either method. In the case of the filters, replacement of the elements becomes necessary from time to time, whereas with the electrostatic type of unit, regular cleaning is most important. There are, however, some electrostatic units that have automatic or semiautomatic wash facilities. These, although desirable, may prove an expensive option. 

The essential method to obtain sterile air, whether packed-bed or cartridge filters are used, is to reduce the humidity of the air after compression so that the filter material always remains dry. The unsterilized compressed air must never reach 100% relative humidity. Larger plants install instrumentation with alarms set at about 85% relative humidity. Careful selection of the cartridge design or the design of packed-bed filters will result in units that can operate in excess of three years without replacement of filter media. If a fiber material is used in a packed-bed type filter, the finer the fiber diameter the shallower the bed depth needs to be for efficient filtration. Other filter media are less common and tend to have special problems and/or shorter life. The bed depth of filters is only 10 to 18 inches for fibers of less than 10 microns. These filters run clean for 2 weeks or longer before being resterilized. 

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