Hydraulic Oil Classifications

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.

This information has been sourced, reviewed and adapted from materials provided by Castrol.

For more information on this source, please visit Castrol.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Castrol. (2019, April 29). Hydraulic Oil Classifications. AZoM. Retrieved on September 18, 2020 from https://www.azom.com/article.aspx?ArticleID=2236.

  • MLA

    Castrol. "Hydraulic Oil Classifications". AZoM. 18 September 2020. <https://www.azom.com/article.aspx?ArticleID=2236>.

  • Chicago

    Castrol. "Hydraulic Oil Classifications". AZoM. https://www.azom.com/article.aspx?ArticleID=2236. (accessed September 18, 2020).

  • Harvard

    Castrol. 2019. Hydraulic Oil Classifications. AZoM, viewed 18 September 2020, https://www.azom.com/article.aspx?ArticleID=2236.

Tell Us What You Think

Do you have a review, update or anything you would like to add to this article?

Leave your feedback