Hydraulic filter elements divide into two main categories: surface and depth. Surface filters typically have a wire mesh construction like, for example, a suction strainer. Depth filters are constructed from a matrix of fibres. Cellulose (paper), plastic, glass and metal can all be used to construct a depth filter.
Man-made glass fibers are smaller and more uniform than naturally occurring cellulose fibers. When glass fibers are woven into a layer, the result is a more consistent pore structure which captures and retains dirt better (high filtration efficiency). Plus glass’s smaller fiber diameter means there’s more of them in a given volume and therefore more spaces to catch and retain dirt. Size for size, this gives glass filter media more dirt holding capacity than cellulose. Glass-fiber elements have the added benefit of superior fluid compatibility. They’re suitable for use with mineral, synthetic and water based fluids.
The superior performance of glass elements does come at cost in terms of the element’s flow resistance and therefore the pressure drop across it. As you’d expect, filter efficiency and pressure drop go together, hand-in-glove. Cellulose elements are low efficiency; low pressure drop. Glass elements are high efficiency; high pressure drop–all other things equal.
And as is often the case, with higher performance comes higher price. Cellulose elements are cheap to buy; glass are not. But this is not the whole story. Because it’s not the absolute price of the element that matters. It’s the dollars per gram or ounce of dirt captured and retained that matters. With this in mind, glass filter elements can last three to five times longer than equivalent cellulose elements. Which means if you’re doing a detailed cost comparison, don’t forget to include the cost of carrying out the element changes. If a glass element lasts three times as long, you save two filter changes. If it lasts five times as long, you save four filter changes.
But don’t forget, if you’re considering changing the elements in existing filter housings from cellulose to glass, be sure to check that the increase in pressure drop created by the higher efficiency element is not going to cause problems–like putting the filter on bypass, for example.
Bottom line: not having the right type of filters in the right places can be a costly mistake in terms of hydraulic system reliability. And to discover 6 other costly mistakes you want to be sure to avoid with your hydraulic equipment, get “Six Costly Mistakes Most Hydraulics Users Make… And How You Can Avoid Them!” available for FREE download here.