Choosing the Proper Filter

Among the more important factors that must be taken into consideration when choosing a filter for a particular application are the size, shape, and hardness of the particles to be removed, the quantity of those particles, the nature and volume of the fluid to be filtered, the rate at which the fluid flows, whether the flow is steady, variable, and/or intermittent, the system pressme and whether that pressme is steady or variable, the available differential pressme, the compatibility of the medium with the fluid, the fluid temperatme, the properties of the fluid, the space available for particle collection, and the degree of filtration required. Let s examine how some of these factors affect filter selection. 

The materials from which the medium, the cartridge hardware, and the housing are constructed must be compatible with the fluid being filtered. Fluids can corrode the metal core of a filter cartridge or a pressure vessel, and the corrosion will in turn contaminate the fluid being filtered. Thus, it is essential to determine whether a fluid is acid, alkali, aqueous, oil- or solvent-based, etc. 

Flow rate (the imits of measurement are given as volume per unit of time, e.g., ml/min, gal/min) is dependent on two general parameters, pressme (P) and resistance R). Flow rate depends directly on pressure and inversely on resistance. Thus, for a constant R, the greater the pressme, the greater the flow. For a constant P, lowering the resistance increases the flow. 

Pressure can come from any number of sources and is usually expressed as poimds per square inch (psi) or bar gauge (barg). All other factors being equal, if the pressure on a fluid is increased, then the flow rate of that fluid will increase. 

Viscosity is the resistance of a fluid to the motion of its molecules among themselves in other words, a measure of the thickness or flowability of a fluid. Water, ether, and alcohol have low viscosities heavy oils and syrup have high viscosities. Viscosity affects resistance directly. If all other conditions remain constant, doubling the viscosity in a filter system gives twice the original resistance to 

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The effectiveness of the air purifying respirator depends on choosing the proper filter, cartridge or canister for the type of exposure present. Air purifying respirators rely on the use of activated charcoal or other chemical-specific filters, which remove gases and vapors, or filters which remove particulates such as dusts. Others utilize a combination of both. 

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