INDUSTRIAL HYDRAULICS AND PNEUMATICS (22655)

MARKET SURVEY OF OIL USED IN HYDRAULIC SYSTEM

HYDRAULIC FLUID PROPERTIES

The properties and characteristics of any hydraulic oil are vitally important to the capability of
your hydraulic system to work within the operating conditions you need to use it in. This is
especially true of industrial or commercial hydraulic oils. So, for a hydraulic oil to be useful it
needs to have the below properties:

 Non-compressible
 Thermally stable, within a range of operating temperatures
 Fire resistance
 Non-corrosive to its system
 Anti-wearing to its system
 Low tendency to cavitate
 Tolerance to water (resistance to water contamination)
 Total water rejection
 Constant viscosity, regardless of temperature
 Long life
 Cost-effective

Few, if any, fluids perfectly meet the above criteria. However, there is a comprehensive range of
hydraulic oils that specialise in meeting the above properties for the set of conditions in which
they are required to operate. Those conditions can range from being required to operate in low
temperatures (winter hydraulic oil), high temperatures and a variety of others.

CONTENTS OF HYDRAULIC OIL

Hydraulic oil is made from a variety of different ingredients, with one base fluid. These
ingredients can often be mixed depending on the type of oil you require.

Generally speaking, hydraulic liquids are made up of:

 Mineral oil
 Esters
 Glycol
 Silicone
 Ethers
 Esters

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HYDRAULIC OIL ADDITIVES

Depending on how you use our hydraulic oil, there will be extra additives which help it perform
under different conditions. Different hydraulic fluid additives include:

 Anti-wear – helps prolong the life of equipment and machinery, you’ll see this on AW-
type hydraulic fluids.
 Cold Flow – additives that enable usage in extreme cold weather conditions
 Anti-foaming – An anti-foaming agent for hydraulic oil reduces foaming within the fluid
which can be 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 while also
reducing sludge deposits.
 Anti-rust – Forms a protective coating which reduces the risk of rust damage from
oxygen contact.

These additives are used on their own and together in different blends which are created for
different purposes. Hydraulic oil properties can be altered depending on which additives are
used, but the typical characteristics tend to be a high viscosity index and be incompressible.

HYDRAULIC OIL CLASSIFICATION

The classifications of hydraulic oil are a subgroup of different fluids with varying performance
levels. Below is a list of common hydraulic oil classifications and their respective descriptions:

HL – Refined mineral oils with anti-oxidation and anti-rust properties

HM – HL with improved anti-wear properties

HR – HL oils with VI improvers

HYDRAULIC OIL RATING

When an additive company sells an additive pack, it will work alongside a particular
manufacturer to create a product which works perfectly with that manufacturer’s application.
This will be traceable by a hydraulic oil supplier who has used the additive in the fluid.
Hydraulic oil ratings or approvals are stipulated by many end users of oil to ensure they’re using
the correct fluid for their equipment.

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HYDRAULIC OIL ANALYSIS

Commonly known as condition monitoring, a hydraulic oil analysis service is used by people
who want the most out of their oil before they have to change it in their hydraulic application.

This works by sending a sample of the hydraulic oil to a lab which analyses the sample and
reports back with details as to whether it’s good to use further or if it needs to be changed. This
gives the end user reassurance that it is still usable and no damage can be done to expensive
equipment due to dirty or worn oil.

IMPORTANCE OF OIL ANALYSIS

The importance of oil analysis should be high on anybody’s list. Below is a list of just a few
reasons why it shouldn’t be ignored and how it pays for itself many times over:

 Reduces the cost involved in replacing the oil prematurely.

 Minimise damage to your machinery by identifying issues early.
 Has the potential to enhance the life and performance of machinery.
 Reduces the risk of damage to machinery and products.
 Reduces the risk of injury to people and further costs in claims and damages.

HYDRAULIC OIL TEMPRATURE RANGE

Depending on the application of hydraulic fluid, it may be subject to cold or hot temperatures. In
some cases, hydraulic oil can be subjected to both hot and cold temperatures which can render
the oil useless if it hasn’t been blended with the right additives.

Hydraulic fluids have temperature stability which means they’ll retain their properties within a
particular temperature range. Anything above or below this will negatively affect the temperature
stability and cause the fluid to either wax and freeze under cold conditions or lose viscosity and
potentially leak under hotter temperatures. High heat can cause rapid deterioration of hydraulic
oil.

HYDRAULIC OIL VISCOSITY INDEX

To measure the change in viscosity of hydraulic oil when the temperature changes, we use the oil
viscosity index (VI). If a hydraulic oil has a low viscosity index, a temperature change will alter
the viscosity more than if it has a high viscosity index.

Hydraulic oil with a high VI will usually be required in an application which is subjected to a
greater range of ambient and/or operating temperatures.

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A straight paraffinic mineral base oil will typically produce a fluid with a low viscosity index,
whereas a paraffinic mineral base with viscosity improvers will produce a fluid with a high
viscosity index.

The SAE (Society of Automotive Engineers) created a classification table (VI Scale) to show
low to high viscosity levels depending on temperature °C. Originally the scale only went up to
100°C but with advances in hydraulic oil blends, the scale now goes above this number!

Viscosity index Classification

0-35°C Low
35-80°C Medium
80-110°C High
110°C and greater Very High

HYDRAULIC OIL CLASSIFICATION

The classifications of hydraulic oil are a subgroup of different fluids with varying performance
levels. Below is a list of common hydraulic oil classifications and their respective descriptions:

HL – Refined mineral oils with anti-oxidation and anti-rust properties

HM – HL with improved anti-wear properties

HR – HL oils with VI improvers

For a detailed list, you can speak with our knowledgeable team by calling us on 0330 107 1358
or alternatively, you can read our explainer of Hydraulic Oil Classifications. Find out Crown
Oil’s hydraulic oil product specs.

HYDRAULIC OIL RATING

When an additive company sells an additive pack, it will work alongside a particular
manufacturer to create a product which works perfectly with that manufacturer’s application.
This will be traceable by a hydraulic oil supplier who has used the additive in the fluid.
Hydraulic oil ratings or approvals are stipulated by many end users of oil to ensure they’re using
the correct fluid for their equipment.

HYDRAULIC OIL GRADES

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ISO VG – ISO Grade (where ISO is the International Standards Organisation) – the higher the
VG number the more viscous the fluid is. The VG number tells you which hydraulic oil is
thicker. This is sometimes referred to as the hydraulic oil weight. At the same time, grades with a
W next to them indicate the weight (Unlike automobile engine oil which refers to winter oil).

AGMA Grade – American Gear Manufacturers Association – Leaders in the standards of gear
oils.

SAE – Society of Automotive Engineers

In the UK, ISO VG is used mainly for grading hydraulic oil. Below is a list of common hydraulic
oil ISO grades ;

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CONCLUSION
With the development of hydraulic technology, the performance requirements of hydraulic oil
are getting higher and higher, and the specifications and standards of hydraulic oil are
constantly updated, which makes the hydraulic oil evaluation technology also need to be
updated. At present, the evaluation of hydraulic oil mainly includes physicochemical properties
evaluation, anti-wear performance evaluation and oxidation performance evaluation, etc. Due
to the special characteristics of the military equipment use environment, in addition to the
above assessment, also need to focus on the low temperature cold start ability of the hydraulic
oil. However, there is less research in this area, and the existing low temperature research
cannot meet the military needs. Therefore, this paper builds a bench test to evaluate the low-
temperature cold start performance of hydraulic oil to provide a reference basis for the
reasonable oil requirements of military equipment.

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REFRENCES

https://www.crownoil.co.uk/guides/hydraulic-oil-guide/#What_is_hydraulic_oil

https://www.google.com/search?
q=hydraulic+system+working&tbm=isch&chips=q:hydraulic+system+working,g_1:simple:USq
GZK_Jw04%3D&hl=en&sa=X&ved=2ahUKEwjj-b6j5_uEAxXP4zgGHT-
eA3QQ4lYoAXoECAEQMw&biw=1349&bih=641

REFRENCE BOOKS

 Industrial Hydraulic and Pneumatics – by Purushottam Balasao Pawar –Sankalp

Publication ISBN 8194556422, 9788194556428
 Oil Hydraulic System-Principal and Maintainance – by Mujumdar S R – McGraw Hill ,
New Delhi (2002) ISBN: 9780074637487
 Fluid Power with Application – Esposito Anthony- Pearson Education, Inc New Delhi
(2003), ISBN : 81-7758-580-0

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