Spin-On Return Line Filters: The Good, The Bad and the Ugly
Spin-on hydraulic canister filters are a cost-effective type of filter but they are not all created equal. When making a choice, consider the following:
- Does it have pressure differential indication or a gauge? If it doesn’t, do you know when to change the oil? Most hydraulic fluids can last years or longer, if kept clean, cool and void of moisture.
- Is it “Fully Loaded”? Major manufacturers rate a filter as “fully loaded” when the pressure drop or delta P is between 15-25 pounds per square inch (psi). After that, the filter tends to increase delta P exponentially, meaning it will load up at a fast rate over time. If the filter portion of a canister gets loaded up with particles from your hydraulic system, it will clog the small pores in the filter element. As a result, the fluid can’t travel as fast through the element, causing a large pressure drop. Excess back pressure can cause filter failure, splitting and metal rupture. If you filter return oil with a loaded element, the element can collapse around 100 psi and nothing will be filtered. Your one line of defense before failure of the exterior canister is the design safety factor. This is typically 2.5 times the Maximum Allowable Operating Pressure Drop (MOPD), which averages 150 psi. If the canister fails, either the back pressure reached over 450 psi or it’s an inferior product.
- Is it the right thread size? Over 50 companies sell spin-on return line hydraulic filters and the top manufacturers private label for other companies. So… are they all interchangeable? Definitely not! Recently, a customer asked for a replacement filter. He provided a part number to a company I had never heard of, and it didn’t match any of the interchange guides available. With the outside dimensions, we narrowed it down to an industry standard size, but it didn’t screw on to the connection. I had assumed it was 1.5” or 1” NPT, but it turned out to be a metric BSPT thread. There are a few companies that make a filter to fit on that connection, but they are European and delivery time is lengthy. Ultimately we changed the filter head to readily available US standard filter sizes.
Hopefully this will help you the next time you need to choose a Spin-on Hydraulic canister filter.