Buying guide for best hydraulic filters
Anyone who uses heavy equipment understands that proper maintenance is a requirement that can’t be overlooked or slighted. The Greeks have a saying, “Careless merchant, future beggar,” that seems to encapsulate this concept. If you don’t take care of your equipment, eventually — and probably sooner rather than later — your equipment is going to let you down. The right filter helps a hydraulic system work efficiently.
Although the main function of the oil is to provide energy transmission through the hydraulic system to accomplish work, it has other uses as well. It cools the system, lubricates the moving parts to prevent wear and tear, removes contamination, and seals the system. The hydraulic filter is responsible for keeping the oil clean so it can carry out these functions.
Choosing a hydraulic filter for your equipment is more complicated than just buying the cheapest one you can find. The filter needs to fit your equipment and machinery and be able to reliably keep the oil clean. We can help you find the right filter for the job.
Key considerations
Equipment size
The size of your hydraulic equipment will determine the size filter you need. The filters reviewed here are not designed to work well with smaller equipment. They are manufactured for large machinery such as tractors and log splitters.
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Features
Media
This refers to the material inside the filter that captures contaminants. Regardless of which material is used, it starts as a flat sheet that is then folded or pleated. This provides more surface area of the filter media in a given container. There are three main filter media: wire mesh, cellulose fiber, and fiberglass.
Wire mesh: These filters are constructed from metal wires (stainless steel is best) woven together in a tight net-like screen. Because the mesh is metal, it has the advantage of being reusable. The filter can be taken out, cleaned, and replaced. However, due to manufacturing and wire size limitations, there is a limit to how small the mesh can be. The finer micron sizes aren’t available in wire mesh filters.
Cellulose fiber: “Cellulose” is a fancy name for wood pulp. The “paper” used for hydraulic filters isn’t much different than ordinary writing paper. It does, however, have the advantage of being cheap. There are a couple of disadvantages, though. One is that cellulose isn’t very efficient. It doesn’t have a large particle-holding capacity. Paper filters need to be changed more frequently than any other kind. And cellulose absorbs water. If you’re using a water-based oil as a fire-prevention measure, these filters will quickly absorb the water in the oil and become clogged.
Fiberglass: Fiberglass is a synthetic material that consistently performs better than cellulose. The fibers can also be manufactured to produce a finer mesh than wire. Many fiberglass filters have multiple layers of differing size and quality. This creates a filter that is extremely efficient, with a large capacity to hold contaminants. These filters are more expensive than cellulose and cheaper than wire mesh.
Efficiency
Filter ratings are often misunderstood and can even be deceptive. The three ratings are nominal, absolute, and beta.
Nominal rating: Manufacturers use a nominal rating, essentially an arbitrary size value they assign to the filters they build and sell. Independent tests have demonstrated that filters nominally rated at 10 microns (μm) have allowed 200 μm particles to slip through. Although manufacturers are fond of nominal ratings for advertising purposes, they don’t have any real meaning or value.
Absolute rating: An absolute rating specifies the largest size particle that can pass through a given filter media. There isn’t any industry-standard test for ensuring filters live up to their claims, but it is still better than the nominal rating manufacturers prefer to use.
Beta rating: The beta (β) rating is based on the multi-pass method for evaluating filtration performance of fine lube filter elements (ISO 16889:1999). The method tests the number of particles of a given size upstream of the filter and then again downstream from the filter. The resulting numbers are used in a ratio that is multiplied to reveal the percentage of the filter’s efficiency. Absolute filters are required to have a rating of βx ≥ 75% (where x = micron size). Anything below that point is considered nominal.
Temperature
Although atmospheric temperatures don’t directly affect hydraulic filters as such, they do affect the viscosity of the oil passing through the filter.
Viscosity and viscosity index are two different but related numbers. Viscosity refers to the thickness of the oil and its ability to flow. The viscosity index shows the change in viscosity due to changes in temperature. The higher the number, the more stable the oil, and the less the viscosity will change with the temperature. The lower the number, the less stable the oil, and the more the viscosity will change. This becomes important to your choice of filters if you live in northern states where the temperatures fluctuate during the year.
Low viscosity index (VI): If you use mineral-based oils, they have a low VI of between 90 and 105, so they become thicker in winter. It will be difficult for the oil to penetrate a paper filter, and it could even wind up tearing through it, introducing cellulose particles into the oil as contaminants. In that case, the stronger wire mesh filter would be a better choice.
High viscosity index (VI): Synthetic oils have a higher VI of around 160, so they are more stable in the winter. If you’re able to use synthetic oil in your equipment, you’re free to choose whichever filter you prefer.
Particulate size
The beta rating for filters specifies “x” as the micron size, but that size differs depending on the tolerances of various machines. Hydraulic component clearances vary considerably. For example, an actuator has a 50 to 250 μm clearance, but an anti-friction bearing has a clearance of only 0.5 μm
Contamination code: Hydraulic systems and their filters are tested then assigned an ISO 4406 Contamination Code. The ISO 4406 chart can be found online. It consists of three columns of numbers. The contamination code also consists of three numbers in an x/y/z format. These numbers for your equipment will tell you which filter you need to buy.
X: The first number specifies the number of particles per milliliter above 4 μm in size. If the number is 20 μm, you scroll up the first column until you find 20, then read the numbers in the associated columns on the right. In this example, those numbers are 5,000 and 10,000, so the number of particles > 4 μm would be 5,000 to 10,000 per milliliter.
Y: The second number indicates the number of particles > 6 μm per milliliter.
Z: The third number is the number of particles > 14 μm per milliliter. You use the ISO 4406 chart to find the results the same way as with the first number.
Hydraulic filter prices
Inexpensive: Under $10 is the low price range for hydraulic filters. You get what you pay for with these. They work, but they don’t last very long.
Mid-range: The medium price is $10 to $20. Most hydraulic filters are in this price range.
Expensive: Above $20 is the high price range for hydraulic filters. These filters will last longer and filter out smaller particles.
Tips
- Don’t change the filter early. It’s a waste of money.
- Don’t overtighten filters when you put them on.
- Check your filters regularly. That way, you won’t forget to change them.
FAQ
Q. Are paper filters just paper?
A. These filters are mostly paper with some synthetic material added for strength.
Q. When should I change the filter?
A. There are no hard and fast rules, but when the oil pressure begins dropping and won’t come back up, it means the filter is clogged and needs to be changed.
Q. How long will the hydraulic oil last?
A. With proper filtration and filter changes, the hydraulic oil can potentially last for years.
