Choosing the right hydraulic fluid is vital to achieve optimum performance

Hydraulic Fluid: A Key Engineering Component

Choosing the right hydraulic fluid is vital to achieve the maximum performance and life for your hydraulic cylinder.

Compatibility Critical

Hydraulic oil or hydraulic fluid is much more than something you add to your hydraulic system like a consumable item.

It is a central engineering component. Choosing the right one is vital to getting the best performance from your hydraulic cylinder. It is also a critical factor in the life of the cylinder and mean time between failures.

For example, hydraulic fluids which are not compatible with the seal material can result in chemical attack where the fluid causes the seal to swell, lose memory due to excessive friction while swollen, or become gummy and sticky.

Beyond the obvious problems that a sticking rod might cause, faulty seals also allow the ingress of water, air or both. Such contamination further reduces the effectiveness of the hydraulic unit and can also lead to internal cylinder corrosion.

Getting the hydraulic fluid right therefore requires looking beyond the application to the construction of the cylinder as a whole and how this comoponent fits in with the whole assembly.

Prevention is Better Than Cure


If you have doubts about the hydraulic fluid you are using then it is better to have it tested than wait for failure. Testing the oil or fluid will provide a better understanding of the state of the fluid in two key areas:

1 - Contamination

Knowing the level of contamination will give vital clues as to any other possible problem such as seal wear or leakage.

The contamition level provides an indication of how much life is left in the system to allow a planned repair to be made in a controlled shut down.

2 - Chemical Makeup

The chemical makeup of the fluid is something that will change over time in line with usage, load and heat. Time may also be factor in itself.

Understanding the chemical makeup will give an indication of the efficiency of the system and when the fluid should be changed in the future.

The downside of testing is the cost and that the results are after the fact. That is, you may be getting the results when it is already too late.


A planned maintenance routine can be used to both prevent problems occuring and spot new problems before they become critical.

Performance information from the manufacturer can be used to establish replacement intervals in line with expected chemical changes under the expected load/application.

Where possible the system should be bled of air. The frequency this occurs has to made on a case by case basis, but it is important to feed back into the routine the results of the bleed. For example, if the amount of air bled seems excessive perhaps it should be checked more frequently.

Unexpected results are of course useful inicators of unexpected failure conditions.

Preventive Measures

Whilst a pro-active preventive maintenance regime is very important so is specifying the assembly system to fit the application.

This often means not taking original equipment manufacuturers at their word about the performance limits of their machine and consulting with a hydraulic cylinder specialist such as The Cylinder Service Centre to see how the core setup could be improved.

The result may be suggestions such as changing the fluid to protect the seal as mentioned above, or using a higher specification fluid, or increasing the level of filtration.

The reduced likelihood of unplanned breakdowns, longer maintenance intervals and reduced maintenance costs can more than offset the upfront cost of any potential modifications.


It is easy to view something that is soft and fluid as a secondary to the hard metal construction of a hydraulic cylinder.

Nothing could be further from the truth as it is the hydraulic fluid that bears the load. Its engineering properties are therefore vital to the success of the assembly.

Understanding the critically important role plays is vital to day to day performance efficiency of the cylinder and its working life overall.