Once you determine what type of hydraulic filter to use, you must consider the pressure drop through the filter. In most cases, pressure filters and return filters have a bypass that protects the system when the filter gets clogged or plugged. It allows the oil to go around the filter element and allows the system to run even though it’s not being filtered. Do keep in mind that your system would be running unfiltered with this setup.
As your filter becomes dirtier, it requires more pressure to push the oil through the element because it is clogged with dirt and debris. Once the pressure required reaches a certain point it becomes inefficient and starts wasting horsepower in the hydraulic system; this is the reason for the bypass. Typically, bypass settings on pressure filters are 40-50 PSI to limit this inefficiency.
When sizing a pressure filter, generally we would like to keep the pressure drop through the filter under 10 PSI. This gives your filter more time to get to the 50 PSI bypass setting, thus increasing the length of time between element changes. If you size your filter with a 25 PSI pressure drop you are already at half of your filter life (assuming 50 PSI bypass). If we selected a filter that only had a 10 PSI pressure drop, your filter will have 40 PSI of pressure drop before it reaches bypass setting, thus, allowing the element to last longer before needing service or be replaced.
Another consideration is oil viscosity. Thicker oil will cause a higher pressure drop, so you need to know what oil you are going to run in your system to truly size the filter correctly and get the best filter life for your application.
