TECHNICAL REFERENCE
Filter Design and Construction There are two main differences in a filter. The first is the design of the filter itself, and the second is the type of media that is used in the filter. Filter Filters have some attributes that are immediately obvious to the casual observer, such as height, inside diameter, outside diameter, media concentration, type of liner, seal design, and the way the media and components are glued or potted together. Liners Liners must be structurally sturdy to withstand pressure variance, yet open enough to allow good flow. Seals The top seal design must be leak-free, with a gasket or sealing device that ensures a good seal throughout the life of the filter. Standard seals are made of Buna-N ® material, which is fine for most applications. However, if the filtered fluid is diester or phosphate ester fluid, you’ll need a seal made of a fluoroelastomer such as Viton ® . Buna-N ® and Viton ® are registered trademarks of E. I. DuPont de Nemours and Company. Media Potting Media potting is key since it holds the media in place in between the end caps (not visiable). Not only should the potting be fully around the ends of the media to prevent leaks, it should also be of a material that can withstand the application. For instance, epoxy potting should be used in filters that must perform in higher temperature environments, phosphate ester fluids and some high water based fluids.
Inside the filter, the media can vary in thickness, pleat depth and pleat concentration.
For example, Donaldson hydraulic filters are generally equipped with either white (“Synteq ™ ” our synthetic material) or natural brown (paper or cellulose material) media. It is important to note that media colors vary according to each manufacturer – it should not be assumed that any white-colored media is made of synthetic material. Some of the most important characteristics of filter media (structure, fiber diameter, volume solidity, basis weight, thickness, layering) can only be detected under a microscope.
Damaged Equipment Damage happens when key filtration points are ignored! The pistons in this pump are severely damaged from contamination in the oil.
Hydraulic Filters & Accessories • 27
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