Criteria for Hydraulic Filter Selection

Blog | August 4th, 2019

When choosing a hydraulic filter, the fluid sieving architecture is expected to satisfy a long list of performance requirements. There’s a brief pause while product parameters are pored over. With all possible selection criteria reservations finally settled, the contamination blocking component is installed. Two separate system stages have been reviewed during this process. First came the filter element, then there was the housing and its valving configuration.

Two-Stage Hydraulic Filtration Solutions

To be fair, that’s the minimum number of components in a hydraulic filtration unit. For the purposes of maximizing structural clarity, let’s start off with a simpler architectural model. In this simplified layout, there’s the filter element, which is seated inside a filter housing. It’s this inner stage that does all of the contaminant-sifting hard work. Checking off the criteria headings on a filter elements catalogue, there are different media types to examine. The choices for filtration material vary from simple steel wire mesh to pleated microglass fibres. Lower micron openings are next on the parameters list. Sure, groups of microscopically small element apertures will block the tiniest, most microscopic particles, but there’s a consequential pressure drop to combat, too. For every gain, there’s a matching system loss to offset, it seems. Enter the second stage, the filter housing, which provides more flow spread. With the element media experiencing a pressure drop, a large diameter filter housing counteracts this flow-choking effect.

Regulating Tug-of-War Criteria Impact

So far, the two stages seem to balance each other out. If a hydraulic filter uses a low-micron microglass fibre, then its housing will use a large-diameter cylinder or cartridge-style housing to offset this effect. Further offsetting such flow-attenuating effects, there are valving arrangements to consider. A bypass valve is considered a common product supplement, and then there are gauge ports and reversing valves as well. Influencing all of these fittings and media types, the maximum flow rate and system pressure receive first mentions. The operating temperature of the fluid also deserves an entry in the criteria selection list, for large temperature fluctuations are carried in hydraulic oils. By the way, as important as any of these flow attenuating factors, the actual properties of the fluid base will clearly have a direct effect on a hydraulic filter’s selection criteria.

Engineers look at the filtration media, at their aperture micron size and material fibres. From here, they choose the bypass valves and porting arrangements on the filter casing. Regarded as the glue that holds the selection process together, numerous flow parameters tie everything up in an intelligently ordained package of fluid sieving parts. Flow temperatures, flow rates and flow pressures usually occupy this section of a filtration benchmarking datasheet.

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