Hydraulic Fluids
Background & Properties
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May 2025
GPS
Industry Specifications
Hydrolytic Stability and Anti-wear Additives
Whether the customer uses a hydraulic fluid that emulsifies or demulsifies, the fluid must still be hydrolytically
stable. Hydrolytic stability refers to the oil's ability to maintain performance during water contamination.
Unstable wet hydraulic oils under high operating temperatures can cause anti-wear compounds to break
down. Once this occurs, the zinc compound is no longer providing anti-wear protection and other chemicals
can cause wear to hydraulic components. As a result, component life can be decreased by 50% or more.
Hydrolytic Stability (ASTM D 2619)
is test measures the oil's ability to protect against wear in the presence of water. It is run at 2030 psi for 250
hours at 1440 RPM.
Test Criteria:
Copper Weight Loss, mg maximum 0.2
Acidity of Water, mg KOH, maximum 4.0
Load Test FZG (DIN 51354, Part 2)
is test evaluates a hydraulic fluid's ability to withstand heavy shock loads.
Test Criteria Damage Load Stage, min
US Steel 136 10
DIN 51524 Part 2 10
GM (LS-2) LH, 03, 04, 06 10
HF-O Report
Hydraulic fluids containing extreme pressure additives are better equipped to handle heavy shock loads.
4-Ball Wear (ASTM D 2266)
is test measures an oil's anti-wear and anti-weld properties. It is run for 1 hour at 54°C, 1800 rpm and 20 kg.
Test Criteria Scar Diameter, mm max
US Steel 127 0.5 (40 kg)
US Steel 136 0.5 (20 kg)
4-Ball EP (ASTM D 2783)
is test evaluates extreme pressure and anti-weld properties of the oil.
Test Criteria US Steel 136
Weld Load (kg), min 150
LWI (kg), (min) 30
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