A Buyer’s Guide to Hydraulic Filter and Lube Filter Replacements
Fourth Quarter 2022 — Hydraulic Systems & Components
Hydrasales specialises in hydraulic and lubrication filtration equipment. Filtering surfaces are divided into two main groups, suitable for a wide range of applications including return line, suction, inline, low-pressure, and high-pressure filters.
Surface Filtration
Surface filtration prevents particles larger than the pore size from entering the system by direct interception. The filter media typically consists of metal mesh material and is used in strainer applications and suction lines or lube systems where higher contamination levels are acceptable.
Depth Filtration
Depth filters are made of overlapping fibre mats that form various flow paths. Particles are trapped in pores smaller than the particle diameter. When using inorganic fibres (commonly called microfibres), multiple layers are placed together to increase the element’s efficiency in capturing contaminants.
Within depth filtration, maintenance teams typically encounter two types of media with different filter efficiencies:
- Nominal (paper) filter cartridges: Single-layer cellulose fibres reinforced with resins. These may have the correct micron rating but lower filtering efficiency.
- Absolute filter elements: Multi-layered constructions with up to six layers of filtering material, including microfibre, metal mesh, and PET protective layers, offering superior performance and durability.
Buyers are often tempted to replace microfibre elements with cheaper cellulose paper filters of the same micron rating. However, reducing filter efficiency allows higher contamination thresholds, increasing breakdowns and repair costs due to leaking seals, component failure, and downtime. Replacing a microfibre element with a cellulose fibre element can reduce filtering efficiency by up to 50%.
Filter Beta Ratios and Efficiencies
Two filters with identical sizes and micron ratings can have entirely different internal structures and cleanliness capabilities. Filtering elements should comply with ISO 16889: Hydraulic Fluid Power — Multi-pass Method for Evaluating Filtration Performance of a Filter Element.
The efficiency of microfibre and paper filters is measured using the Multi-pass Test. The beta ratio is the ratio between the number of particles of a specified size upstream of the filter and the number downstream. The higher the beta ratio, the greater the filter’s capture efficiency.
For example, a cellulose paper element typically has a beta-2 ratio with 50% efficiency, while a microfibre element reaches 99.9% efficiency (beta-1000). Therefore, it is essential not only to consider the micron rating but also the beta ratio and efficiency at that particle size.
