Hydraulic Oil Classifications - Supplier Data by Castrol

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Hydraulic Oil Classification Descriptions


The function of a hydraulic fluid is to provide a means of power transfer in a hydraulic circuit.  The fluid must lubricate the pumps and motors without impairing the function of the other components in the total hydraulic system. 

Hydraulic Oil Classification Descriptions

HH      Non-inhibited refined mineral oils

HL      Refined mineral oils with anti-oxidation and anti-rust properties

HM      HL with improved anti-wear properties

HR      HL oils with VI improvers

HG      HM oils with anti-stick slip properties

HS      Synthetic fluids with no specific fire resistant properties

HF *   Symbol for fire-resistant fluids, with additional letters according to type

HFAE   Oil in water emulsions or aqueous solutions containing max 20% mass of combustible materials

HFAS   Solutions of chemicals in water containing min. 80%mass water

HFB     Water in oil emulsions containing max 25% mass of combustible materials

HFC    Aqueous solutions with viscosity-increasing additives and minimum 35% mass water

HFD    Fire-resistant non-aqueous fluids which are further divided with additional letters according to type

HFDR   HFD based on phosphoric acid ester

HFDS   HFD based on halogen-containing compounds

HFDT   Mixtures of HFDR and HFDS

HFDU   Fire-resistant fluids of other compositions.

* The above classifications of HF-type fluids describes only the fluid category without taking into consideration any characteristics except fire resistance.


Source: Castrol


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