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Background & Properties
Industry Specifications
Hydraulic Fluids
July 2017
Cold Start (Up ASTM D2983)
Used to evalute ability of oil to be pumped or flow in cold temperatures.
KRL Shear Test (20 hours)
Bench test method that compares the permanent shear loss of multigrade hydraulic oils. Recent tests have shown that
the 20-hour test provides excellent correlation to actual field and pump test performance. During this test, the
lubricant is tested in a tapered bearing fitted to a four-ball EP test machine.
Test Criteria
% viscosity loss @100°C 15% max
Filterability, Demulsibility and Foam Tests
Water Tolerance: Demulsify or Emulsify?
Two major concerns for maintenance managers are keeping water out of a hydraulic system, and then dealing with it
once it inevitably enters the system. Water can enter a hydraulic system in a number of ways: loose fill caps, poor
seals, loose tolerances on the suction side of components, use of a pressure washer, condensation in the sump and
even by contaminated top-off fluid that has been compromised during storage or delivery. Once in the system, water
is to blame for problems like wear, power fluctuations, rust and the overall destruction of sensitive components.
Knowing how a hydraulic fluid handles water can inevitably save your customer time and money in maintenance.
Separating Water from Oil
The best way to handle water contamination is with proper maintenance practices and an excellent hydraulic oil. AW
hydraulic oils demulsify, or separate water from oil. This allows for the water to be drained from the sump, preferably
at the beginning of each work shift. There should be a clear delineation between the water and oil. A white, creamy
cuff between the water and oil or cloudy hydraulic fluid means the oil is not properly demulsifying and additive dropout
may be occurring.
Mixing Oil with Water
If maintenance practices or system design do not allow for the daily removal of water, a fluid that emulsifies is the next
best choice. Fluids that emulsify oil and water are ones that mix with the water to create an emulsion, fully enveloping
the water. This eliminates free-circulating water, but must be weighed against possible tradeoffs like wear protection
and proper viscosity grade selection.
How a hydraulic fluid deals with water contamination is one of the vital questions that needs to be answered when
determining the hydraulic fluid for a customer. At the same time, internal maintenance practices need to be evaluated
to assure that system maintenance coincides with the fluid's handleability to water (emulsify or demulsify).
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