Section 3 - Types of Filter

Abstract

This chapter explores many different types of filters that are available for processes such as strainers, presses, and filters aided by magnet, electricity, or centrifugal force. The filters are divided by the force that causes filtration: vacuum (i.e., a negative pressure at the filter medium), gravity alone (i.e., the hydrostatic head of the liquid above the medium), centrifugal force (i.e., an amplified gravity effect), fluid pressure (imposed by the suspension feed pump), mechanical pressure (a squeezing effect), and the use of other force fields. The large number of types of pressure filters is obvious—for most people the pressure filter, from simple cartridge to the complex fully automated filter press, typifies filtration. The range of gas filtration equipment is much smaller than that for liquids. This is because the recovery of solids from a gas suspension is a task not often undertaken in a filter, a cyclone being used instead. Gas filtration is almost always a decontamination process, whether it is of inlet air to buildings or machinery, or of exhaust streams from machines or processes. Solids recovery from liquid suspension, on the other hand, is a task frequently undertaken by filters, and the wide variety of types of liquid filters is almost entirely because of the problems imposed on filter design by the need to remove these collected solids from the inside of the filter.