Hydraulic fluid plays a vital role in every hydraulic system we use. Also, we can say it as the heart of a hydraulic system. Hydraulic system performance is directly related to what type of fluid you have chosen for the application. The three major roles that a hydraulic fluid performs are:
- Power transfer
- Heat transfer
In this article, we offer information on the different hydraulic fluid types
Hydraulic Fluid Types
It can be categorized into different types based on hydraulic fluid properties like viscosity, thermal stability, hydrolytic stability, anti-wear characteristics, etc… Not every fluid satisfies all these properties. So, if you want to select a hydraulic fluid, you need to analyse what all are required properties. That is if your application works at a higher temperature, then the selected fluid must have high thermal stability.
All the major hydraulic fluids come under the following two categories.
- Fire Resistant Hydraulic Fluid
- Petroleum Base Hydraulic Fluid
You can learn more about the subcategories of these types in this article.
Fire Resistant Hydraulic Fluid
Commonly fire-resistant hydraulic fluids are used in hydraulic systems that are installed in hazardous areas like mining industry, aviation industry, automobile manufacturing, etc... The fire resistance benefit of this hydraulic fluid makes the environment and workers safe. One of the major drawbacks of fire-resistant hydraulic fluid is the need for proper maintenance and checking. Contamination or low fluid level can be a reason for premature failures of your hydraulic system.
Also, Read: Functions of Hydraulic Fluid
Water-based Fire Resistant Hydraulic Fluids
Water alone is not used as a good hydraulic fluid. Because the lubrication properties, thermal stability and corrosion resistance of water are comparatively poor. Although, still water is used as a hydraulic fluid with certain applications when it mixes with oil and addictives. Mainly there are three types of water-based fire-resistant hydraulic fluids. They are discussed below.
1.Water Glycol Type
This fluid is also known as HFC hydraulic fluid. It is a mixture of water and glycol. The solution contains 40 % water and 60 % of glycol. This hydraulic fluid type has excellent viscosity and low-temperature properties that makes it adaptable for a temperature between 120°F-130°F (49°C to 54°C).
2. Water in Oil Emulsion (W/O)
Around 60- 65% of oil is used in this W/O emulsion. Normally this fluid is compatible with most of the seals and materials. Comparatively, this W/O fluid has good lubrication properties than other types of water-based fire-resistant hydraulic fluids. The desired temperature for operation ranges between 120°F - 130°F (49°C - 54°C) and above 150°F the water will evaporate and fire resistance decreases.
3.Oil in Water Emulsion (O/W)
HFAE is the common name for the oil in water emulsion. This category of hydraulic fluid contains a low concentration of oil. This fluid contains approximately 1-5% of oil and there are chances for bacterial control and corrosion-related problems.
Water Free, Synthetic Fluids
The operating temperature of the synthetic hydraulic fluid (another name of water-free fire-resistant hydraulic fluid or HFD fluid) ranges from 175°F- 200°F. This category of fluids contains chemicals that can attack hydraulic system components like plastics, zinc and cadmium. HFDR, HFDS, HFDT, and HFDU are the four categories of water-free, synthetic fire-resistant fluid. HFDR fluids are used in the mining industry and contain phosphorus acid ester. HFDS fluids contain chlorinated hydrocarbons and are used for hydrodynamic clutches. The fluid that is used for hydrostatic transmissions containing mixtures of phosphorus acid ester and chlorinated hydrocarbons are called HFDT fluids. Other synthetic fluids without water content compatible for aviation hydrostatic are called HFDU fluids.
Also, Read: Is Hydraulic Fluid Flammable
Petroleum Base Type Hydraulic Fluid
Petroleum-based hydraulic fluids are highly flammable. So, they are most commonly used in applications without any risk of fire, temperature variation and no environmental issues. This fluid is ideal for different applications, mainly for mobile equipment. Some of the benefits include non-corrosiveness, high lubrication characteristics, easy availability and inexpensive. The only problem is the low flashpoint. This types of fluid are made by refining crude oil to the desired level and by adding addictives to it for improving fluid properties. Petroleum-based hydraulic fluids are categorized into three.
- Additive Turbine Oil
- General Hydraulic Oil
- Special Purpose Hydraulic Oil