In hydraulic elevators the base oil typically does not wear out.  The additive package may be depleted and some of the oil may oxidize, but the bulk of the oil can be scrubbed.

Oil that oxidizes is no longer oil; it is chemically changed into oxidation byproducts which can be removed from the oil using depth filtration.  Due to the large volume of oil in hydraulic elevators, most of the oil is not oxidized because it does not encounter the heat zones in the pump, valve or elbows.

The AW additives are smaller than the filtration capacity of the scrubber.  However, depleted or neutralized additives will attach to metal or debris in the oil which are large enough to be filtered out of the oil by the scrubber.

According to the EPA Animal fats and vegetable oils are regulated under 40 CFR 112, which has identical requirements for petroleum and non-petroleum oils.  Petroleum oils, vegetable oils, and animal fats share common physical properties and produce similar environmental effects.

Source: www.epa.gov/emergency-response/vegetable-oils-and-animal-fats

Varnish in solution cannot be filtered when the oil is over 40°C (104°F); below 40°C the absorption capability of the cellulose insert can remove varnish.  Typically the reservoir temperatures decrease during off-peak hours enabling varnish removal during oil scrubbing.

The smell associated with hydraulic elevators is the result of acid in the oil due to oxidation.  Scrubbing the oil can remove the particles, varnish and reactive material that the acid is attached to.  When the acid is removed, the smell should go away.

Oil is incompressible compared to air.  A bouncy or springy feel, especially at the upper floors, is the result of air entrainment in the oil.  Water contamination contributes to air entrainment, so water removal is the solution to air entrainment.

Transfer carts are designed to move oil quickly, but with speed comes a loss of filtration capability.  Typically transfer carts have nominal 10 micron to 15 micron filter.  The particles that are most likely to contaminate the valve on a hydraulic elevator are around 5 microns.  The Oil Scrubber™ has a 3 micron absolute filter and is over 98% efficient.