Have you Got Cloudy Hydraulic Oil?
Brendan
Casey
Brendan Casey has more than 16 years
experience in the maintenance, repair and overhaul of mobile and industrial
hydraulic equipment. For more information on reducing the operating cost and
increasing the uptime of your hydraulic equipment, visit his web
site: http://www.InsiderSecretsToHydraulics.com.
Why is water in hydraulic fluid bad?
Water in hydraulic fluid:
- Depletes some additives and reacts
with others to form corrosive by-products which attack some metals.
- Reduces lubricant film-strength,
which leaves critical surfaces vulnerable to wear and corrosion.
- Reduces filterability and clogs
filters.
- Increases air entrainment ability.
- Increases the likelihood of
cavitation occurring.
How much water is too much?
A number of factors need to be
considered when selecting water contamination targets, including the type of
hydraulic system and reliability objectives for the equipment. It's always wise
to control water contamination at the lowest levels that can reasonably be
achieved, ideally below the oil's saturation point at operating
temperature.
Water removal methods
Methods for removing free (unstable
suspension) and emulsified (stable suspension) water include:
- polymeric filters;
- vacuum distillation; and
- headspace
dehumidification.
Vacuum distillation and headspace
dehumidification also remove dissolved water.
Polymeric filters - These look like conventional
particulate filters, however the media is impregnated with a super-absorbent
polymer. Water causes the polymer to swell, which traps the water within the
media. Polymeric filters are best suited for removing small volumes of water
and/or maintaining water contamination within pre-determined limits.
Vacuum distillation - This technique employs a
combination of heat and vacuum. At 25 inches Hg, water boils at 133°F (56°C).
This enables water to be removed at a temperature that does not damage the oil
or its additives.
Headspace
dehumidification -
This method involves circulating and dehumidifying air from the reservoir
headspace. Water in the oil migrates to the dry air in the headspace and is
eventually removed by the dehumidifier.
In the case of small systems with
high levels of water contamination, changing the oil may be more cost-effective
than using any of the above methods of water removal.
Prevention is better than cure
Like all other forms of
contamination, preventing water ingress is cheaper than removing it from the
oil. A major point of water ingression is through the reservoir headspace. Many
hydraulic system reservoirs are fitted with breather caps that allow moisture
(and particles) to enter the reservoir as the fluid volume changes through
either thermal expansion and contraction, or the actuation of cylinders.
