The Ultimate Hydraulic Oil Guide | Hydraulics Online (2024)

• Viscosity: how well the fluid flows in certain temperatures;
• Low temperature fluidity: ease of flow under low temperatures;
• Thermal and oxidative stability: preventing contamination through a sludge build-up;
• Hydrolytic stability / water tolerance: preventing contamination through water;
• Cleanliness and filterability: regular maintenance ensures reduced contamination;
• Demulsibility: ability of the component to filter out water from the oil;
• Anti-wear features that improve the life of components;
• Corrosion control: preventing corrosion of the components;
• Biodegradability and managing environmental impact.

Hydraulic oil includes mineral oil and esters. The latter is a carbon-based compound, which is created by substituting the hydrogen of an acid with an alkyl. Other main elements in hydraulic oil include: glycol, silicone and ethers. The latter is a highly flammable, volatile liquid containing an oxygen atom which links two alkyl.

Other chemical additives are added to most hydraulic oils in order to maintain or improve the performance of both the oil and the equipment within the hydraulic system. They can prevent corrosion, rusting and also water contamination. It is vitally important to always choose the appropriate oil for your system. In fact, the wrong oil can cause performance issues and in more severe cases, permanent damage to your system and components.

Most hydraulic components and systems use oil-based hydraulic fluids. There are, however, circ*mstances when oil should be avoided. For example in applications with potential ignition sources; sparks, open flames, hot metal. In such hazardous environments, a leak from a high-pressure hydraulic system could create an explosion or a serious fire. The term “ATEX” comes from the French “atmosphere explosibles” and is the name commonly given to the framework for controlling explosive atmospheres.

There are many different types of oil for a wide range of applications and it is important to choose the right oil for your system.

There are three main groups of equipment and areas that hydraulic oil can be found in: mobile, industrial and aviation. Each one of these requires different types of hydraulic oil depending on the conditions they are operating in and the demands placed on the equipment.

The hydraulic oil viscosity depends on how smoothly it flows. For example, if viscosity increases, then it will take longer for the oil to pass through the hydraulic system. Moreover, high viscosity means the oil is thicker and is more difficult to transport through a system.On the other hand, lower viscosity means the oil is easier to pass through the system.

The measurement of viscosity in hydraulic oil is taken in Centistokes (cSt) and most commonly at temperatures of 40°C and 100°C.

Hydraulic oil viscosity is vital when choosing the right hydraulic oil for your system. In hydraulics, there’s a direct relationship between hydraulic oil viscosity and its temperature. For instance, if the temperature of the oil increases then the viscosity decreases. Similarly, when you put cooking oil into a pan and heat it up, the oil moves faster the longer it is heated. A temperature drop makes the oil move less easily and it becomes more viscous.

Hydraulic oil viscosity needs to be able to work effectively to enable smooth operation no matter the temperature. This is particularly important as applications become more demanding.

The viscosity index helps us to measure the change in temperature in hydraulic oil. A lower viscosity index means that the oil may be more susceptible to change than if it were a higher viscosity index. Moreover, if the viscosity is high, the oil will be better suited to an application which is used in harsher environments, exposed to a variety of operating temperatures.
The viscosity must be accurate for your application and the temperature. This is true even if the oil has properties include anti-wear, anti-oxidisation or anti-corrosion. An incorrect viscosity could result in damage to hydraulic equipment, problems during operation and reduced service life.

The table below shows the classifications of viscosity against different temperature ranges:

Although gear pumps are classed as the most inefficient out of all of the pumps, they are still able to function through a large amount of contamination. They work by expelling fluid once it has been pressurised between the meshing teeth in the pump. Gear pumps come in two variations: internal and external.

Internal gear pumps are usually available in a variety of viscosities, ranging up to 2,200 cSt. With high efficiency and reduced noise, these pumps typically operate under pressure from 3,000 – 3,500 psi.

Although external gear pumps are less proficient than there counterpart, they still offer easy maintenance, stable flow and are cost-effective when it comes to purchasing and repairs. Similarly to the internal gear pumps, external gear pumps produce pressure between 3,000 – 3,500 psi – however, their viscosity range only reaches 300 cSt.

It’s important to maintain healthy hydraulic systems and components and there are proven methods to help you look after your hydraulic oil.

Modern hydraulic systems are typically a lot smaller and more compact than they used to be. This means that less oil is used during operation. Pumps can also produce a lot more output, subsequently producing higher pressures. Less oil within the system also means higher fluid temperatures – which in turn, increases oxidation and thermal stress on the additives on the oil. However, engineers still want the most cost-effective oils that last as long as possible and still operates faultlessly.

The hydraulic oil longevity depends on a few influences: the quality of the oil, working conditions and possibly even contamination. However, within the right environmental factors, a high quality oil should be able to last at least six months. And with the right maintenance and up-keep, the hydraulic oil life should be able to last even longer.

Oxidation is the process of the conversion of hydrocarbon molecules in to carboxylic acids. As we’ve said before, higher temperatures can reduce the life of the hydraulic oil, as it quickens the oxidation process. The by-products made from oxidation eventually form a varnish, which subsequently can block filters and suction strainers. If oxidation becomes a big issue, changing the oil immediately is the best course of action.

Moreover, contaminants (such as water, air, dirt, fuel, and other oils or lubricants) are a common issues that can have a detrimental effect on hydraulic oil life.

1). Ensure that any oil you have in your system is of high quality and from a supplier who can provide technical support when needed;

2). Keep an eye on operation conditions. Make sure the fluid is always kept clean;

3). Always ensure oil is changed if oxidation or contamination become too much.

• Anti-wear: lengthens the service life of hydraulic components and machinery;

• Cold flow: these additives enable a system to operate in extremely cold environments;

• Anti-foaming: an anti-foaming agent for hydraulic oil reduces foaming within the fluid which is sometimes caused by detergents. This foaming can reduce the lubricating quality of the product thus causing damage;

• Anti-oxidant: allows for longer periods of use without an oil change and also reduces sludge deposits;

• Anti-rust: forms a protective coating which reduces the risk of rust damage from oxygen contact.

A hydraulic filter is an essential component of any hydraulic system. Moreover, selecting the right hydraulic filter is absolutely vital to protect oil life and ensure that particle contaminants are removed from the hydraulic fluid before components are jammed or damaged through abrasive wear.

We have widespread, competitive access to both leading and niche hydraulic filtration equipment manufacturers from around the world, includingATEX approved – “explosion proof”– hydraulic filtration components.

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