Type and Selection of Hydraulic Oil

Different hydraulic fluids are used for different operations of the hydraulic systems. factors similar to electrohydraulic servo faucets, electrohydraulic servo mechanisms, detectors, etc. need to perform with different hydraulic fluids.

It’s first necessary to establish fine details of hydraulic oil for the design and analysis of the hydraulic system. In this article, we will learn about:

  1. Analyzing hydraulic oil
  2. Ingredients and content of the hydraulic fluid
  3. Different types and benefits of hydraulic oil
  4. Hydraulic viscosity and Its different grades.

What is Hydraulic Oil?

Hydraulic oil properties

Hydraulic oil is a kind of fluid that can be used for several functions. It serves as a medium of energy transfer or power transmission medium, lubricant, and sealant. Also, with the help of this fluid equipment can cool down and carries contaminants away.

Based on the types of hydraulic systems we use different types of hydraulic fluid. For eg., Hydraulic fluids for hydrodynamic applications are called power transmission oils. while hydraulic fluids for hydrostatic application are hydraulic oils.

When we think of fluid for lubrication, Hydraulic oils are the most important lubricants following engine oils. As the major areas of hydraulics are static, dynamics, and aviation hydraulics. If used optimally, hydraulic oil can save energy, and reduce machine and component wearing. So, it extends maintenance intervals and increases machine life.

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Why hydraulic oil Analysis is Important?

Analysis of hydraulic oil is important and should be on a high-priority list during selection. Below points are just a few reasons that should be kept in mind:

  • It helps to reduce the cost involved in replacing the oil prematurely.
  • Helps to minimize damage to your machinery by defying issues before time.
  • It is capable to enhance the life and performance of machinery.
  • Helps to minimize the risk of damage to machinery and products
  • Reduces the risk of cost pertaining to injury of people and further expense and claims.

Contents of Hydraulic Oil

Hydraulic oils are made from multiple ingredients, with one base fluid. All of these ingredients can often be mixed as per requirement depending on the type of hydraulic oil requirement.

In general, hydraulic oils are made with the following ingredients:

  1. Mineral oil
  2. Esters
  3. Glycol
  4. Silicone
  5. Ethers
  6. some chemicals which according to required properties.

For various applications of hydraulic fluid, blenders will mix the base oil with additives of different types to make the hydraulic oil with the required properties.

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Types of hydraulic Oil

Almost all the above oils are of the same type but vary in their working characteristics and viscosity. According to the functional characteristics and viscosity, their additives change slightly. According to that, the following types of hydraulic oil are there:

  1. Hydraulic oil.
  2. Slide oil
  3. Generator oil
  4. Turbine oil
  5. Compressor oil
  6. Spindle oil
  7. Gear oil

Main Hydraulic oil Raw material

Mainly following components are used for the formation of hydraulic oil:

  1. Mineral oil
  2. Anti-wear agent
  3. Anti-oxidant
  4. Rust preventives
  5. Pour point decreaser
  6. Viscosity index improver
  7. De-emulsifier
  8. Anti-foam agent

Important properties of hydraulic oil

Depending on the type hydraulic oil have certain properties to meet the requirement of the hydraulic system and operating condition. Whether the hydraulic oil is heavy duty or required for normal working conditions, hydraulic oil must have the following properties:

  1. It should be non-compressible.
  2. its viscosity should be stable in a provided range of operating temperatures.
  3. It should not catch fire.
  4. It should not be corrosive in nature.
  5. Anti-wearing
  6. Should not mix with water
  7. Durable

In addition, hydraulic oil also should be “cost-effective“. A single hydraulic oil can not meet all the requirements. That’s why hydraulic oils are manufactured and formulated according to different conditions in which they will need to work.

Benefits of Hydraulic Oil

Different types of hydraulic oil and based on their application and additive package, it has different benefits. In general, mineral oil or synthetic oil-based hydraulic oil can have the following benefits:

  1. This protects against corrosion and rust. In other words, hydraulic oil is hydraulically stable.
  2. Optimized operation in extreme working conditions because of viscosity stability.
  3. The system’s efficiency, reliability, and performance can be increased as hydraulic oil protects from foaming and sludge formation and its deposit.
  4. Hydraulic oil protects the hydraulic system when exposed to air and water as it has anti-oxidation properties.
  5. Hydraulic oil possesses the property of a contaminants eliminator. Because of that, the hydraulic system maintains its filtration efficiency.
  6. As we know, Oil quickly separates water and prevents damage. Hydraulic equipment is protected against water emulsion. This property of oil is called demulsiblity.
  7. Some hydraulic oils are biodegradable and can operate in sensitive environments.

Why is cooling required for Hydraulic Oil?

After the continuous operation of the hydraulic system temperature of the whole increase which can reduce the working efficiency of hydraulic oil. One of the major reasons behind heat generation is friction.

Every hydraulic device is normally equipped with a cooling system for the removal of heat. But in the case of a non-functioning of colling system or insufficient cooling, oil temperature rises which can generate the following problems as listed below:

  1. Stopping of equipment in case of abnormality– To prevent the major problems related to the operation of the equipment described in items 2 to 4 below, the operation of the equipment is stopped by an interlock system if the oil temperature reaches a certain level. Normally the interlock system is activated at temperatures of between 60 and 70 ℃, at which the rise of the oil temperature can cause adverse effects.
  2. Decrease in the hydraulic oil’s viscosity– A decrease in the viscosity reduces the lubricating performance, causing wear of sliding parts and in the worst of cases burning, which could cause the equipment to stop operating.- A decrease in the viscosity increases the fluidity of the hydraulic oil, increasing the speed of operation of the actuators, which could speed up wear and deterioration and induce critical damage.
  3. Deterioration of packings– Deterioration of rubber parts in the sliding and rotating sections and the packings used at the joints of pipes can lead to oil leaks that could affect the operation of the pump and actuators.
  4. Deterioration (oxidation) of the hydraulic oil– If the temperature of the hydraulic oil itself remains high for an extended amount of time, the oil oxides, turn dark reddish-brown.
    Oxidation decreases the various elements of the hydraulic oil’s performance and could corrode the device, so oxidized oil must be replaced. More frequent oil replacement increases running costs and the operational workload.

Difference between Hydraulic Oil and Hydraulic Fluid

Most of the time many people use the same term either for hydraulic oil or hydraulic fluid interchangeably. While there is a small difference between the two:

Hydraulic OilHydraulic Fluid
It consists of oils and additives that are specifically designed to transmit power and also act as a lubricant or coolant to the system. Hydraulic oil reduces corrosion and is widely effectiveIt has similar use as hydraulic oil but has wider use in automobile systems for automatic transmission, power brakes, and steering. Additionally, aircraft systems also require hydraulic fluid as it is lightweight, and easy to install and maintain.

Hydraulic Oil Viscosity Index

The oil viscosity index is a measure of hydraulic oil viscosity when the temperature change. If hydraulic oil has a low viscosity index, it means a change in temperature will alter the viscosity more and vice-versa.

Hydraulic oil with a high oil viscosity is generally required in applications that are subjected to a greater range of ambient or operating temperatures. A paraffinic mineral base oil will typically produce a low viscous index. Whereas a paraffinic mineral base with the addition of viscosity improvers will produce a fluid with a high viscosity index.

The Society of Automotive Engineers creates are classification table to differentiate the viscosity index depending on temperature as follows:

Viscosity IndexClassification
0-35 Degrees CelsiusLow
35-80 Degrees CelsiusMedium
80-110 Degrees CelsiusHigh
110 Degrees Celsius and moreVery High

Hydraulic oil grades

Hydraulic oils are used in industrial machinery with low loads to heavy loads. Accordingly, different grade of hydraulic oil is to be used. There are 06 grades of hydraulic oil in general as follows:

  1. ISO 10 Hydraulic Oil: ISO VG 15 Hydraulic Fluid is typically used in power steering and hydraulic brake systems.
  2. ISO 15 Hydraulic Oil: ISO VG 15 Hydraulic Fluid is typically used in power steering and hydraulic brake systems.
  3. ISO 22 Hydraulic Oil: ISO VG 22 Hydraulic Fluid is generally used in airlines for air tools etc.
  4. ISO 32 Hydraulic Oil: ISO VG 32 Hydraulic Fluid is ideal for use in high-powered machine tools.
  5. ISO 46 Hydraulic Oil: ISO VG 46 Hydraulic Fluid is normally required for industrial plants working under high-pressure etc.
  6. ISO 68 Hydraulic Oil: ISO VG 68 Hydraulic Fluid is designed for use in systems that require a large load-carrying ability.


Hydraulic systems are the core of many industries, from craft to mining. As such, these machines operate in extreme climatical and dealing conditions. Unsurprisingly, hydraulic oils are essential for any hydraulic system’s performance.

Apart from their core role as energy transporters, they additionally function as sealants, lubricants, and coolants. Hydraulic oils additionally play a core role in the removal and interference of contaminants. exactly owing to that, opt for the finest hydraulic fluids with advanced additive packages.

When it involves hydraulic fluids and additive technologies, Valvoline has forever been AN business leader. we have a tendency to boast a good choice of premium, standard, and perishable hydraulic oils.

All fluids from our choice enhance the performance of hydraulic systems, permitting them to control spotlessly at each and low operational temperature. They forestall corrosion, dust, foaming, and wear.

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