One
of the most common problems faced while working with hydraulic equipment
is the clouding of oil. The problem of cloudy oil is essentially caused
when the oil is contaminated with water beyond its saturation level, in
other words, the dissolution of water within oil more than its holding
capacity, leads to oil clouding. The saturation level of hydraulic oil
varies between 200 – 300 ppm at 68°F (20°C). A given
amount of cloudy hydraulic oil confirms the presence of at least 200 –
300 ppm of water.
Negative effects of water contaminated hydraulic oil
Water contaminated
hydraulic oil
renders adversities like possible cavitation and reaction with various
materials to form corrosive by-products, attacking other constituting
metals. Besides, it also affects the hydraulic system by increasing the
air entertainment ability. Reduction of lubricant film-strength and
filterability are other major side-effects of cloudy hydraulic oil.
Methods for water removal from hydraulic oil
Polymeric filters, Vacuum Distillation and Headspace Dehumidification
are the various methods used for the removal of Emulsified(stable
suspension) and Free(unstable suspension) water. Vacuum Distillation and
Headspace Dehumidification can also be used for the removal of dissolved
water.
Polymeric filters:
These filters
come across as the conventional particulate filters, but the media
within, carries a super-absorbent polymer. Water makes the polymer
swell, which then makes the water to trap within the media. Polymeric
filters can very well be used for removing relatively small volumes of
water or alternatively, maintaining water contamination levels within
the saturation limits.
Vacuum distillation:
Vacuum Distillation process uses the
technique of heat and vacuum. The contaminated hydraulic oil is
calculatingly boiled at such a level that the water is removed without
effecting the oil or its additives. For example: At 25 inches Hg, water
boils at 133°F (56°C) thus, diminishing the water content
while maintaining the oil and the additives as well.
Headspace Dehumidification:
Under this method, the air is
circulated and dehumidified from the reservoir headspace, making water
in the oil migrate to the dry air in the headspace and getting it
removed by the dehumidifier in the final stage.
Though in case of small hydraulic systems with high levels of water
contamination, changing the entire amount of oil is most cost-effective
solution rather than using any of the above mentioned methods of water
removal.
Control water ingression within the hydraulic system
Water contamination in hydraulic systems can be tackled using any of
the above discussed water removal methods, but its always better to
safeguard the
hydraulic fluids from
excessive water. One of the major leak way for water ingression is the
reservoir headspace. Most of the hydraulic system reservoirs are fitted
with breather caps that let the moisture enter the system, such standard
breather caps can be replaced with hygroscopic breather to control the
ingression of moisture and particles through reservoir's vent.
