Return Line Filter
The return line filter strains the oil coming back to tank from the actuator and is the most common filtration point in the system. Typical element rating is 10-25 micron and permitted pressure drop is in the 1-3 bar range. It catches wear generated particles before they reach the tank.
Because pressure is low in the return line, the housing can be inexpensive and the element large. On the other hand, return flow rate coming from the cylinders can be higher than pump flow rate because of the area difference; filter size must be chosen according to this peak value.
- Clogging indicator: most housings have an indicator showing the pressure difference. The reading must be taken while the oil is at operating temperature; with cold oil the indicator misleadingly goes to red.
- Replacement: once in the first 50 hours, then according to the manufacturer's interval.
- Bypass: when the element clogs, oil passes unfiltered; if the indicator is warning, the element is effectively out of service.
Filtration needs do not change when a kit converting a manual lever to electronic control is fitted, but machine usage time generally increases. Tracking the filter interval by operating hours rather than by calendar is the cheapest way to keep proportional behavior from degrading over time.
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