Filters of the viscous impingement type

utilize a filtering medium relatively coarse in texture and constructed of fiber, screen, wire mesh, metal stampings or plates.


The medium is coated with a viscous substance such as oil or grease. As the many small air streams abruptly change direction thin the filter, contaminating particles are thrown against the medium where they adhere.

Efficiencies of 65% to 80%, based on the weight method of testing, are achieved in the case of cleanable media. This type of filter is available in a throwaway style or may be obtained with a replaceable medium, a manually cleanable medium, or an automatically renewed medium. Media designed for filtering velocities of approxImately 300 feet per minute usually increase in density  in the direction of the air flow.

Thus, the larger particles are the first removed, prolonging filter life. High velocity filters operating at approximately 500 feet per minute are normally nondirectional and of uniform density.

The former consists of a moving filter roll.

The latter is constructed of overlapping filter panels attached to a moving chain and moving thru an oil bath. In either case the filter curtain may he actuated by a timing mechanism or a pressure sensing device. Automatic filters present a relatively constant resistance to air flow, while panel filter resistance varies considerably as the dust load increases. Automatic filter efficiencies vary from 80 % to 90 % , based on the weight method.

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