Contributed by Josh Cosford
Are filters a one-size fits all type of product? Certainly not. When selecting a filter, you must understand where the ideal location for that filter will be. You also need to do an overall assessment to determine if one filter is enough or if you should install multiple filters throughout your system.
Most hydraulic systems use a single return line filter, most often either an in-tank unit or an inline spin-on filter assembly. Return filters are typically the most economical and practical, if only one filter must be used. They clean all fluid returning from the system, which removes any internally generated particles. You should be careful when selecting return line filters, however, because spikes in both pressure and flow can occur in return lines.
Pressure filters are common for use after the pump, effectively safeguarding downstream components from particles either ingested into the reservoir or generated by the pump itself. You can even purchase pressure filters without a bypass valve, which normally allows flow to circumvent the filter when it begins to clog.
When ultimate filtration is required, an offline system is most efficient. Offline filtration requires a dedicated pump and motor to circulate tank flow through an often very fine filter with high dirt holding capacity. Often called a “kidney loop” filter, these systems run even with the machine does not, and are not exposed to unstable operating conditions related to the primary circuit. The downside is the added expense of an additional pump, motor and filter assembly.
Regardless of which location you install your filter (which is, of course, all three), ensure it operates using a bypass indicator. The bypass indicator comes in either a pop-up device, a pressure gauge or lighted switch. When backpressure measured in the filter reaches a preset point – typically between 60-80% of bypass valve cracking pressure – the indicator warns you the element must be soon changed.