A vast inventory catering for different hydraulic oil specifications can be very expensive!

What if you could use a different specification hydraulic oil? How much do you think you could save in consolidating your hydraulic fluid stock holding?

To many this would seem like a nonsensical question, but to a company with a large fleet of earth moving equipment, keeping a comprehensive hydraulic fluid inventory can be a nightmare.

As an example,
a fleet owner may have the following equipment: Bucket trucks, cranes, backhoes, rollback wreckers, dump trucks and scissors lifts. Each piece of hydraulic equipment often requiring different hydraulic oil specifications: Warren R&O, Conoco MV-22, NAPA AW-46 and AW-315.

Would it be possible to rationalise some of these to cut down on inventory?

First you need to understand all the different hydraulic oil specifications.

The first step is to decipher all of the different abbreviations and numbers to understand what you've got, so you can compare "apples to apples".


 This task is complicated by the different standards used in categorising hydraulic fluids. And, some abbreviations and numbers used by individual manufacturers are not standard at all.

Looking at the above array of hydraulic oil specifications:

• R&O stands for rust and oxidation - mineral oils with improved anti-rust and anti-oxidation properties. The ISO classification for these oils is HL. 
• AW stands for anti-wear - R&O oils with an anti-wear additive package. The ISO classification for these oils is HM. 
• MV stands for multi-viscosity. This is not a standard abbreviation. In theory, MG (multi-grade), MW (multi-weight) or HVI (high viscosity index) could all be used to mean the same thing. Regardless, these oils contain viscosity index improvers which modify the rate of change in viscosity with temperature. The ISO classification is HR for VI-improved R&O oils and HV for VI-improved AW oils. 

Now to the numbers:

• 22, 46 and 315 refer to the viscosity grade (VG) of the oil; 22 and 46 are ISO grades and refer to the oil's kinematic viscosity in centistokes at 40 degrees Celsius, plus or minus 10 percent. 
• So, an ISO VG 46 hydraulic oil has a viscosity of between 41.4 and 50.6 centistokes at 40 degrees Celsius. 
• Viscosity grade 315 is a now mostly obsolete ASTM viscosity number - 315 SUS at 100 degrees Fahrenheit (40 Deg C), which is roughly equivalent to ISO VG 68.

How to confirm the change in hydraulic oil specification.

In the above example, this equipment would require both R&O and anti-wear hydraulic oil in three different viscosity grades - one of which is VI improved. Looking at these, it may be possible to change to a single hydraulic oil specification - probably ISO HM - VG 46. But to confirm this, each piece of hydraulic equipment must be assessed individually by considering:

• Starting viscosity at minimum ambient temperature (worst-case cold start); 
• Maximum expected operating temperature, which is influenced by the hydraulic system's efficiency and installed cooling capacity, and the maximum ambient temperature at the machine's location; 
• Permissible and optimum viscosity range for individual hydraulic components in the system.

Making the actual change to the hydraulic specification.

Once this has been done and the appropriate type and grade of hydraulic oil have been chosen, the next issue to consider is how to go about changing equipment over to the "standardized" oil.

In this case, because we are only considering three different types of mineral oil, we don't need to concern ourselves with the compatibility of seal materials. But, we do need to concern ourselves with miscibility of the oils.

On this point, you won't get any peace of mind from the oil companies. It's highly unlikely any oil blender will tell you that it's OK to mix its oil with a competitor's - and for good reason, too. When oils with different additive chemistry are mixed, there is always a risk of additive "drop-out".

At the very least, you should be doing a thorough oil drain, reservoir clean and filter change as part of changing hydraulic oil specifications. But unless it's practical or possible to drain every part of the hydraulic system, a small percentage of the original oil will remain and be mixed with the new oil.

A practical test to see if the different hydraulic fluids are compatible.

Before making the switch, it's a good idea to mix equal parts of the original and new hydraulic oil in a glass jar and shake vigorously. Wait half an hour and observe the solution. Look for obvious changes in colour, clarity, viscosity and sediment. Next, filter 100 ml of the original, new and mixed oils through a patch filter - noting the time taken for each. If nothing abnormal is observed, it should be safe to proceed.

Obviously any change to hydraulic oil specifications to rationalise inventory, should be accompanied by a cost saving.

If you wish to reduce operating and power costs even further, consult Habot Synthetic Lubricants about what synthetic hydraulic fluid would be suitable to change your current hydraulic fluid specification with.