Ronald Bakker explains the demands new machinery is placing on hydraulic oils and gives advice on what properties to look for when purchasing an oil to meet the challenge.
Modern machinery developments mean that hydraulic equipment is now smaller, more compact and able to operate at faster speeds. This is good for engineering and manufacturing companies, as they can now install more machinery in a given factory space, substantially increasing productivity. However, these improvements can also place additional pressure on hydraulic oils.

The simple fact is that, unlike the large and older machines of the past, new, more compact machines have reduced oil reservoir capacity, which means less oil is available per cycle.

Also, with new machinery running at faster rates, an increased oil flow is needed.

So, with more power being absorbed by less oil, the hydraulic oil operates at a higher temperature, which can cause the oil to oxidise.

In our experience, temperature significantly affects hydraulic oil performance and lifetime.

Our research shows that for every 100 deg C rise in oil temperature above 700 deg C, oil lifetime reduces by around 50%.

This is why the additives used within the oil play such a crucial role in determining its quality and performance.

When oil oxidises, sludge can form which clogs filters and valves.

This can eventually lead to system failure.

In addition, the oil becomes thicker, which can lead to increased pump noise and more system wear, adding significant maintenance costs.

With the oil capacity of machines reducing and yet the running speed increasing, the oil retention time in newer machinery is significantly shortened, placing further demands on the oil.

For example, an older hydraulic machine with an oil capacity of 600 litres and a pump capacity of 100 litres, has a six minute oil retention time.

In newer systems, the oil capacity is, for example, 300 litres with a pump capacity of 150 litres, reducing the oil retention time to just two minutes.

A shorter oil retention time puts increased pressure on the oil to cope with soft contaminants such as air and water, which are typically picked up during operation.

If the oil fails to shed these contaminants in the reservoir, they will pass through to the pump and circulate in the system.

The build up of such contaminants reduces the quality of the oil, which will ultimately cut productivity and cause equipment damage.

Engineering companies need to ensure that when buying newer models of the same machinery, they check the operating manual and oil requirements in order to understand the likely oil stress.

If the oil is not of sufficient quality, there may be serious effects on the hydraulic system, application and actual finished product.

In the case of water contamination, water needs to be shed from the oil quickly and drained from the system.

If excessive amounts of water enter the system and are not removed, then several problems can occur.

During shutdown time, weekends or annual holidays, water will sink to the bottom of the tank and can cause internal rusting in the reservoir.

In addition, on restart, the first shot of oil will carry a significant amount of water.

As we all know, water is a poor lubricator and excessive water in hydraulic fluids can cause pump damage, corrosion, bearing failure and possible filter blocking due to bacterial growth.

Air in hydraulic fluids is another serious issue and if entrained air is not given enough time to rise to the surface and clear, then the fluid will carry air bubbles around the system.

Air in hydraulic fluids can cause a number of problems including cavitation and 'dieseling' - this occurs when air bubbles collapse under pressure, causing the local temperature of the oil to rise rapidly.

This rapid acceleration in temperature causes the oil to carbonate, which results in the oil turning black and carbon deposits damaging pumps and blocking filters.

Other problems caused by air in hydraulic fluids include spongy controls, loss of power, foaming, poor temperature control, noise, poor lubrication and oxidation.

If cavitation leads to a pump replacement, then as well as changing the pump, you need to change the oil and clean the system of hard particulate contamination.

Our research shows that the lifetime of a pump will continue to decrease if only the pump and oil are changed following the failure.

With all this pressure on hydraulic oils to perform, an effective oil needs to excel in many different areas; anti-wear, air release, demulsibility, filterability, storage, thermal stability, anti-foam, hydrolytic stability and rust.

The DIN (Deutsches Institut fuer Normung, Germany's National Standards Organisation) standard on hydraulic oils sets out the requirements that hydraulic oils must meet.

Engineering companies should treat this standard as a benchmark but to get the most out of their hydraulic machinery they should look at using high performing hydraulic oils which far surpass this standard.

Companies should also refer to specific Original Equipment Manufacturers'(OEMs) lubrication guidelines and/or standards which will meet their individual hydraulic system and production specifications.

In addition, they should contact a reputable lubricants supplier to discuss what type of hydraulic oil will meet their machine requirements.

After all, hydraulic oil is the lifeblood of any system and you must make sure it can cope with the pressure.

* About the author - Ronald Bakker is product application specialist at Shell.