Types of Hydraulic Fluid

There are major five types of hydraulic fluids which meets the need of the system.  Which are as below:

  •  Petroleum-based fluids
  •  Emulsions
  •  Water Glycol
  •  Synthetic Fluids
  •  Vegetable oil

 Other areas under:

  • Biodegradable fluids
  • Fire Resistant fluids
  1. Petroleum-based fluids

Petroleum-based fluids are also called as mineral oils. They are most widely used in the hydraulic system.  Good properties of the petroleum-based oil are as follow:

  •  Excellent Lubricity
  •  High demusibility
  •  More oxidation resistance
  •  Higher viscosity index
  •  Good sealing characteristics
  •  Easy heat dissipation
  •  Easily available
  •   It is flammable
  • At higher temperature, it evaporates and may catch fire.

2. Emulsions

  • Emulsions are a mixture of two fluids that do not chemically react with others.
  •  Emulsions of mostly petroleum-based oil and water are commonly used. Two types of emulsion are in use are as follow.

A.  Oil in water(5:95 ratio) emulsions.

  •  This emulsion has water as the main phase, while small droplets of are dispersed in it.
  •  It has about 5% oil and 95% water, and hence, it exhibits the characteristics of water.
  •  Its limitations are poor viscosity, leading to leakage problems, also loss in volumetric efficiency and poor lubrication properties.

B. Water in oil (40:60 ratio) emulsions.

  •  This emulsion has oil as the main phase, while small droplets of water are dispersed in it.
  •  They are the most popular fire resistant hydraulic fluids.
  •  It is the dilution of 40% oil and 60% water,  they exhibit more of oil-like characteristics.
  •  They have good viscosity and lubrication properties.

3. Water Glycol

  •  Water glycol is another non-flammable fluid commonly used in aircraft systems.
  •  It has water and glycol 1:1.
  •  It has low lubrication properties as compared to mineral oils and it is not suitable for high temperature.
  •  It needs to be added with oxidation inhibitors.
  •  It is very good for low-temperature operation as it possesses high antifreeze characteristics.

4.Synthetic Fluids

  • It is based on phosphate ester, it is another popular fire-resistant fluid.
  • It is suitable for high temp. applications,
  • Good viscosity and lubrication properties
  • Not suitable for low temp. applications
  • Basically being expensive,  requires expensive sealing material (Viton).

5)Vegetable Oils

  •   Increase in global pollution has led to the use of more environmentally friendly fluids.
  •  Vegetable oil are biodegradable and are environmental safe.
  •  Good lubrication properties
  •  Moderate viscosity
  •  Less expensive
  •  Good fire resistance properties with certain additives
  •  Have a tendency to easily oxidize an absorb moisture

Biodegradable Hydraulic Fluids

  •   Organizations are understanding their social responsibility towards pollutions free environment and are turning towards eco-friendly and biodegradable hydraulic fluid.
  •  i.e. sunflower, rapeseed, soybean,  hence cause less pollution
  •  It has similar properties as that of mineral oil-based anti-wear hydraulic fluid.

Fire Resistant Hydraulic Fluids

  •  There is much hazardous application where human safety requires the use of a fire-resistant fluid.
  •  An example includes coal mines, hot metal processing equipment, aircraft, and marine fluid power systems.
  •  Fire-resistant fluids have been developed to reduce or helps to reduce fire hazards.
  • There are four types of fire-resistant hydraulic fluids in common use: 1.Water Glycol solution 2.Water in oil Emulsions 3.Straight Synthetics 4.High Water Content Fluids (HCWFs)

About the author


View all posts

Leave a Reply

Your email address will not be published. Required fields are marked *