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06 Solutions Q&A ? 2.1.3 How do vapor removal filters work? Carbon filters are used to remove oil vapors (odors). The activated carbon has a porous structure which results in a large surface area. The oil vapors are attracted and adhere to this surface. There is usually a small sintered medium included in an activated carbon element to prevent the carbon particles from migrating downstream. The carbon filter reduces the maximum oil content of air leaving the filter to 0.003ppm at 70°F, i.e. To ISO 8573 class 1.7.1. ? 2.1.4 Why use a pre-filter? A pre-filter is simply a general purpose filter placed upstream of a higher grade filter to remove the majority of the water and larger particle contaminants and thus lengthen the life of the higher grade filter element. A 5 micron pre-filter should always be used ahead of an oil or vapor removal filter. 2.2 Air quality ? 2.2.1 What is ISO 8573? This is an international standard on air quality. It covers compressed air for general industrial use. The air quality is specified using a 3 digit code expressing the remaining content of a specific contaminant after the filter (or dryer). ISO 8573 Particle concentration Class Pneumatic fluid power rating 6 5µm 7 40µm ISO 8573 WATER CLASSES (Defines maximum remaining water content) Class Maximum pressure dewpoint 1 -70 2 -40 3 -20 4 +3 5 +7 6 +10 ISO 8573 Maximum oil content (Defines maximum remaining oil content) Class Maximum concentration mg/m3 1 0.01 2 0.1 3 1 4 5 ? 2.2.2 What micron ratings are available? The standard IMI Norgren general purpose elements are 40 and 5 microns, with 40 microns being suitable for most industrial applications. Certain industries have 25 or 75 micron as a standard and some product ranges have these options available. For a given element size, the smaller the micron rating the higher the pressure drop across the filter. The service life between cleaning is also less for the smaller micron filters, as small holes plug more quickly than bigger holes. ? 2.2.3 How do service life indicators work? The service life (pressure drop) indicator found on top of coalescing or general purpose filters is green when the filter is new. As a pressure differential develops across the filter element with use, a spring biased red outer sleeve is pushed up. When more red is visible than green, then the pressure differential across the element is in excess of 0.7 bar and the element should be replaced. ? 2.2.4 When does the carbon pack indicator changes color? The white ring around the base of the vapor removal carbon pack changes color in the presence of liquid oil. Therefore if the ring changes color the coalescing filter is passing liquid oil and needs replacing. Remember that visual detection is a not a substitute for scheduled maintenance. ? 2.2.5 How long does an element last? This depends entirely on the quality of the inlet air. If it is very poor the elements will need replacing more frequently. Filters (cont.)