Hydraulics - Seafish

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Oil A is said to have a low viscosity index and could have a typical
value of 20. Oil B is said to have a high viscosity index and could
have a typical value of 100.
For most hydraulic systems, a viscosity index of at least 90 is
recommended.
The terms viscosity and viscosity index have different
meanings and each value must be considered when
checking if an oil is suitable for a hydraulic system.
The necessary information for checking a hydraulic oil is usually
found in the operator's manual provided by the manufacturers
of the hydraulic system.
Pour point
The pour point of an oil is the lowest temperature at which the oil
will flow satisfactorily.
The pour point of any oil used in a system should be at least 10°C
below the lowest temperature which the hydraulic system is
expected to operate in.
Other Properties
As well as having a suitable viscosity range, viscosity index and
pour point, a hydraulic oil must:
• Prevent rusting.
• Resist the formation of sludge, gums and varnish.
• Resist foaming if air is mixed into it.
• Allow any water contamination to separate from it easily.
• Not attack or dissolve the material of seals and gaskets.
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