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The types of hydraulic oils


Oils are important to creating pressure in the hydraulic systems which are used for applications in a wide range of sectors.

The oils are fundamental to the way hydraulic systems work – they are pressurised fluids which create energy. In this blog, we’re taking a look at which types of hydraulic oils are available, and what applications they are used in, categorised by type application.

We’ll look at the main kinds of hydraulic oils on the market today, and the ways they are used in sectors such as manufacturing, aviation and automotive. First, let’s understand the role of hydraulic oil.

Why is hydraulic oil necessary?

Non-compressible hydraulic oil transfers power within machinery. Not only does it transfer power from one part of a system to another, but some types of hydraulic oil can have the role of a coolant (stopping the equipment from overheating), sealant (preventing contamination) or lubricant (reducing friction).

From high pressure systems in cars for power steering to brakes and industrial machinery, hydraulic oils have a broad variety of applications. The composition of these oils is a base oil, with a selection of chemical additives. Additives boost performance in various ways; both of the oil itself and the systems they are used with.

Hydraulic oil types

Now let’s look at each type of hydraulic oil in isolation:

Synthetic hydraulic oils

These high performance options are produced from chemicals, and are engineered to offer advantages such as optimum lubricity, stability and biodegradability.

While they usually have a higher price point to mineral-based hydraulic oils, synthetic hydraulic oils are often favoured for their performance under high pressures and very high or low temperatures.

There are several different types of synthetic hydraulic oil. Let’s take a look at some of the most common varieties you will see on the market:

Polyol ester synthetic hydraulic oils

This type of synthetic oil offers excellent lubrication and a high degree of fire resistance. These oils have a high viscosity index, meaning that they can provide stable lubrication over a wide temperature range. They are environmentally friendly, being biodegradable.

Phosphate ester synthetic hydraulic oils

Unlike polyol ester synthetic hydraulic oils, which are made from the result of synthesised alcohols reacting with fatty acids, phosphate esters come from aromatic alcohols reacting with phosphoric acids. They offer many of the same benefits that polyol ester synthetic hydraulic oils do, including excellent lubrication thermal stability, fire resistance and eco-friendliness.

Water-glycol synthetic hydraulic oils

Made up of part water and part glycol (an organic compound in the alcohol family), these types of synthetic hydraulic oils are biodegradable and non-toxic, offering fire resistance. However, because the water-glycol type of synthetic hydraulic oils evaporates faster, it is suitable for lower temperatures. You can find these oils with additives that offer anti-wearing and corrosion resistance.

Mineral hydraulic oils

This is the most common type of hydraulic oil, and is made with a base of distilled crude oil, found in rocks. The distilling is necessary to extract hydrocarbons and contaminants. Although synthetic hydraulic oils generally have the edge over mineral oils in terms of performance, additives can increase performance in areas such as lubrication and anti-wearing.
Mineral synthetic hydraulic oils can be solvent-refined fluids or hydrocracked oils with fewer impurities and higher viscosity. You may choose a mineral hydraulic oil over a synthetic variety due to their lower price point, and performance in difficult environments such as mines and construction sites. These conventional pools can offer corrosion and rust protection, and high oxidisation stability, which protects against chemical breakdown due to water exposure in damp conditions.

You can find that many mineral synthetic oils have longer intervals for reapplication – this can make maintenance simpler while also reducing expenses.

Vegetable hydraulic oils

These are derived from the same raw materials you may be familiar with from cooking oils, such as sunflower seeds, canola, and rapeseed.

As vegetable hydraulic oils are natural, they can appeal to environmentally conscious users who want a non-toxic and sustainable product. They have a reduced carbon footprint, because the manufacturing process of vegetable hydraulic oil normally produces less carbon emissions compared to other types of hydraulic oil.

There are other advantages too. Compared to mineral hydraulic oils, vegetable oils have a higher ‘flash point’, offering more fire resistance and thermal stability. They also perform well in providing lubricity to reduce wear and tear.

Applications of hydraulic oil

Now let’s look at the common uses of hydraulic oils, splitting them up into categories according to industry application:

Food grade

Food grade hydraulic oils are specially formulated to meet with safety and quality guidelines in the food production industry. They are designed to be safe to use with equipment and machinery that may come into direct or incidental contact with food. This type of hydraulic oil is free from elements or additives, which may contaminate food products.

From food processing lines to packaging equipment, food grade hydraulic oils have their place in many parts of the food production industry. They are used on a variety of hydraulic systems and components such as compressors and pumps. The same type of oils can also be verified for use in other industries such as pharmaceuticals.

Food grade hydraulic oils perform the role of lubricating and protecting hydraulic systems in food processing facilities. Not only does this prolong the life of machinery, but it can also help to reduce maintenance costs. By offering these benefits, while also helping to ensure that food products are safe and uncontaminated, food grade hydraulic oils can help to ensure that production processes are compliant with relevant regulatory standards.

Environmentally friendly

There are environmentally friendly hydraulic oils which are rapidly biodegradable and designed to break down quickly, reducing the negative impact on the environment. Environmentally friendly hydraulic oils are usually made from plant-based oils and other renewable sources. They don’t contain additives that could harm natural resources and habitats.

These types of oils can be used in hydraulic systems in a variety of environments and industries, from agriculture to construction and industry. They perform the function of most hydraulic oils – that is, to provide lubrication and protection for hydraulic systems and components.

Marine applications, including ships’ hydraulic systems and boat engines, also require environmentally friendly hydraulic oils. By using these types of oils, marine operators can reduce the risk of oil spills harming the marine environment.

As businesses seek to reduce their carbon footprint, protect the environment and tick off corporate social responsibility commitments, rapidly biodegradable hydraulic oils will increasingly be used as an eco-friendly alternative to petroleum-based oils.

Fire resistant

Fire risks are a major consideration when using hydraulic systems in many industries. There is potential for fluid sprays and leaks when lubricants are pressurised. This risk is heightened when a system operates in high working temperatures or is in proximity to open flames.

The conditions described above mean there is a demand for fire-resistant hydraulic fluids. These types of oils – which are typically used with any machinery that operates in high temperatures – include water-glycol fluids, synthetic hydraulic oils and high-water content fluids.


In the automotive industry, hydraulic oils are necessary in various types of vehicles. They allow power to be transmitted through the hydraulic machines on vehicles which carry lifting machines for heavy loads, such as boom trucks or truck-mounted cranes. They are also used for power steering systems and braking systems.

Both mineral and synthetic hydraulic oils are used for this purpose. Mineral oils are favoured for the lubrication and oxidation resistance which they provide, as well as their compatibility with seals and gaskets. Synthetic oils offer lower volatility, superior thermal stability and enhanced low-temperature performance.


Hydraulic oils are vital in aviation. From flight control systems to brakes, landing gears, slats, ramps and access doors – various types of systems rely on hydraulic fluids for safe operation and efficient performance. They allow power to be transmitted through heat transfer, lubrication and corrosion protection.

Synthetic hydraulic oils are widely used in the aviation industry; offering superior performance; withstanding operating conditions with high pressure, extreme temperatures and varying altitudes. There’s also the lower level of volatility and better thermal stability that synthetic oils offer compared to mineral-based oils, giving them appeal for aircraft-related applications.

Phosphate ester-based hydraulic fluids are also utilised for some aviation applications – this type of hydraulic oil provides superb fire resistance, making it suitable for systems such as auxiliary power units and engines, for which fire safety is a huge consideration.

In keeping with the strict procedures and quality control which underpin processes in the aviation industry, hydraulic oil is used as part of regular maintenance and analysis, reducing risks and helping to prevent issues with hydraulic systems.

Power generation

In the power generation sectors, hydraulic oils have a role to play in reliable and efficient operations. They are typically utilised in systems and components such as turbine control, valve actuators, and parts involved in the control of steam flow.

In environments with demanding operation conditions – including high pressures and extreme temperatures – the type of hydraulic oil chosen is critical in power generation. Turbine control fluids are usually petroleum (mineral) oils which offer lubrication and corrosion resistance, as well as thermal stability. Fire-resistant hydraulic fluid is another requirement, being suitable for systems with an elevated risk of fire such as boiler feed pump systems.

Essential for safety and performance

As we’ve seen from this breakdown of the various oil types and applications – hydraulic oils are vital for the safety and performance of systems in many industries. They enable power transfer and are lubricants, coolants and sealants. Due to the broad variety of different applications, it is absolutely essential to purchase the right hydraulic oil for each purpose, including additives that can maximise efficiency.

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