There are major five types of hydraulic fluids which meets the need of the system. Which are as below:
- Petroleum-based fluids
- Water Glycol
- Synthetic Fluids
- Vegetable oil
Other areas under:
- Biodegradable fluids
- Fire Resistant fluids
- 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.
- 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.
- 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).
- 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)