Tank Breather Filter (Breather)
The breather filter is the small but critical element that filters the air entering the tank as the cylinders move. Standard types typically retain down to the 10 micron level; in systems with proportional valves, 3 micron or desiccant types are preferred. This is the most common route by which contamination enters the system.
When a cylinder extends, the oil level in the tank drops and air is drawn in from outside equal to the volume difference. Dust and humid air enter directly above the oil. On a machine running thousands of cycles a year, this means re-injecting dirt into oil that has just been filtered.
- Symptom: dust buildup around the tank cap and a thin layer of sludge on top of the oil.
- Moisture: silica gel desiccant types reduce water condensing during cold-hot cycles; they show their saturation by changing color.
- Maintenance: a clogged breather filter can create a vacuum in the tank and put the pump into cavitation.
This element is especially important in systems with proportional valves; because the clearance between spool and body is on the order of microns, dirty oil leads to sticking, a growing deadband, and degraded repeatability. Checking oil cleanliness before improving the control electronics gives faster results.
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