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. CenterTube Liner Liners must be structurally sturdy to withstand pressure variance, yet open enough to allow good flow. Donaldson’s spiral wound construction allows more flow area without compromising the collapse strength. Sharp edges on holes of competitive tubes can cause media to tear during pleat movement. Donaldson’s louver design has hundreds more flow openings than competitors.The louvers are pushed in towards the inner tube, the surface of which media come in contact with is smooth and pleat tip wear is eliminated. Baffle Plate & Seam Most heavy-duty liquid filters made by Donaldson have an identifiable baffle plate.They also have open ends that turn up for strength and durability. Competitive products have baffle plates that turn down and in. Inner 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 nitrile material, which is fine for most applications. However, if the filtered fluid is diesel or phosphate ester fluid, you’ll need a seal made of a fluorocarbon. Not all competitive filters have a seal between the baffle plate and end cap. Donaldson’s seal is constructed of molded elastomer that is designed for extreme cold and heat. Some competitive brands use paper, cork and plastic spacer materials that do not last for the service life of the filter and may not be leak tight.
End Cap Sealing A leak will occur in a filter when the end plate and filter do not seal completely. Donaldson filter media is embedded deeper in the sealing compound (plastisol, epoxy or urethane). Media Potting Media potting is key since it holds the media in place in between the end caps (not visible). 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. Filter Media 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. Curing is the process that adds strength to the filter media and ensures that filter by-pass does not occur. Donaldson cures filter media while it is in a flat, pleated state to ensure consistent and even curing. Uncured media has very low strength and can rupture easily when saturated with oil. Media Pleating Inside the filter, the media can vary in thickness, pleat depth and pleat concentration. Donaldson liquid filters are generally equipped with either white synthetic or yellow 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. Inner Spring or Grommet These components keep the internal filter compressed against the baffle plate and seal. Donaldson spin-on filters use coil springs and grommets which compress and rebound under extreme pressure. Competitive brands use a leaf spring which, when compressed, will bend and deform, allowing unfiltered fluid to by-pass the filter.
50 • Engine Liquid Filtration
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