As oil laced air passes through the separator, the special
material of the separator causes the oil to adhere. As the oil
collects and becomes heavy, gravity causes the oil to slide down,
and, depending on the compressor model, collects for reuse by the
As the oil collects on the separator it brings dirt and debris
with it which over time will reduce the efficiency of the separator
and can even cause a sudden and unexpected pressure drop.
Since compressed air passes through an air/oil separator, having
a clean separator can reduce the strain on your compressor's
working parts, meaning less energy use and less wear and tear.
The air/oil separator generally starts with a 2 to 3 psi
pressure drop at full load when new. Maintenance manuals usually
suggest changing an air/oil separator when there is a 10 to 12 psi
pressure drop across the separator. In many cases it may make sense
to make an earlier separator replacement, especially if electricity
prices are high.