- 14 March 2007 -

Finding a comprehensive lubricant solution for pumps

Choosing the wrong pump lubricant can result in costly repairs and part replacement. So how can pump engineers ensure they make the right choice? By looking at the whole picture and considering all requirements when choosing a lubricant solution, says Shell’s industrial and aviation lubricants specialist, Steve Greenall.

Pumps are becoming more expensive to produce and maintain, making it more costly and inefficient to replace parts when things go wrong. So says Steve Greenall, an industrial and aviation lubricant specialist at Shell. “With the price of some pumps costing thousands of US dollars, with expensive parts, engineers can’t replace them as easily as they used to and so often.”

Shell is a major supplier of lubricants and greases to the hydraulic pump industry, through its Shell Tellus Oil range. According to Steve, because of the rising cost of pumps, choosing a suitable lubricant has become increasingly important as the cheapest and most reliable way of ensuring that parts last as long as possible.

When anything relating to the hydraulic system is modified, such as temperature, location or pressure, oil thickness and surface roughness, lubricant performance can be affected. “Increased pressure and temperature can drastically affect the lubricant, to the extent that the viscosity is so altered that the pump may fail to operate,” says Steve.

“Viscosity really is key,” he explains. “When it is altered by even a small amount, the hydraulic system’s efficiency can also change dramatically.”

This is when a knowledgeable lubricant manufacturer comes in handy. “Most lubricant manufacturers make calculations about what will happen to the lubricant when modifications are made,” says Steve. “In general, engineers should work more closely with lubricant manufacturers to ensure that parts and lubricants work longer and more effectively and are both considered at the design stage.”

Designing the ideal system
To improve pump reliability over a longer period, choice of lubricant should be taken into account at the design stage, Steve advises. How a lubricant acts can vary widely depending on application, location, temperature and pressure.

“Outdoor pumps need special attention,” says Steve, “because of fluctuating temperatures and atmosphere. Of course, it’s easy to test pumps indoors, because of the easily regulated parameters. But some of our pumps have been used in applications outdoors where the temperatures and conditions were extreme.”

In one example, an open cast mining application in Siberia, it takes six weeks for supplies to be delivered, so the engineers had to ensure that the lubricant chosen was correct and would require little attention in use. Previously, engineers at this site used two grades of lubricant – summer and winter – to cope with the extreme temperature ranges. However, this meant that contamination could occur when the lubricants were changed, downtime was necessary to swap the grades, and the operatives might use the wrong lubricant at the wrong time accidentally. Further, two lubricants had to be sent down the lengthy supply chain to Siberia. Shell provided a new lubricant that could be used all year round, making the plant more self-sufficient. The specified lubricant had to pour at minus 30°C but also have specified viscosities at minus 50°C and between 75/80°C due to cold start and hot operation. The lubricant had to cover all these temperatures, as well as other requirements. “If the lubricant did not perform correctly you can imagine the downtime and maintenance the pumps may have had to undergo,” says Steve.

Contamination
The risk of contamination, (for example, water, air and dust) and how it can affect the lubricant, is another important factor, according to Steve. “Contamination is the most likely thing to happen in the field,” says Steve. Water from the atmosphere, or moisture from the process, can easily contaminate lubricants – especially if it is being used in a marine application. “Water has a big effect on oil, and can affect wet or dry filterability,” Steve explains. As well as contamination through water or dust, some operatives can accidentally pour the wrong fluid into the lubricant section, such as paint, engine oil, or even glue in a recent case. It is important therefore to test the effect of the water on the product (a test known as hydroyltic stability). Shell also performs a range of ‘filterability’ tests, with and without water, and on aged samples. “This is quite a revealing test,” says Steve. Dirt and contamination in lubricants can be more of a problem when running pumps outdoors and extra care should be taken to keep systems clean.

Specific pump systems can be affected more than others by lubrication contamination. “Anything involving fine tolerances can be drastically affected by contamination of the lubricant,” Steve explains. “For example, consider hydraulic pistons on aircraft simulators. Any contamination will result in jerkiness, making it very hard for the user to imagine that he or she is in an aircraft.”

Matching demands
How do lubricants help engineers fulfil the increasing demands of the industry? Pump engineers most importantly want systems to be energy efficient and cost effective by working within an ever-smaller footprint. There are also environmental requirements – Steve gives the example, of the environmental standards regarding the pollution of water by pump lubricants. “Sweden has set up its own specific standard for pumps used near water: the ‘Swedish Standard’, regarding the use of lubricants near water,” Steve says.

To help meet these ever more demanding needs, Shell has improved its lubricants at the lab stage – by running tests on new materials and new additives.

“Lubricants have changed a lot in the past few years,” says Steve. “Engineers should keep informed of all the changes. We may have developed a range of lubricants more suitable to their systems and requirements. The lubricants are designed to match the engineers’ requirements for much longer-lasting fluids. The interest in alternative basestocks has been caused by the increased price of crude oil and a desire to maximise the efficient use of resources. Steve says. “The focus now is on ‘oil life’ even though this means at the end that pump engineers may consume less Shell lubricant.”

So why is Shell encouraging its customers to buy longer-lasting lubricants? “Oil is a diminishing resource. It’s not in anyone’s interest to use it wastefully,” says Steve. “We are genuinely very keen to help the customer make the oil last longer. If you’re not taking that pro-active stance, your business is going to suffer.” Disposal costs are also increasing so it makes good commercial sense to maximise oil life.

Chemical make-up
Lubricants are made up of base fluids and additives – both of which play vital roles in making up the lubricant. The base fluids commonly used include mineral oils (as in the Shell Tellus range), water-based fluids or phosphate esters for fire resistance, biodegradable fluids, such as rape seed and synthetic esters for environmentally adapted performance.

The additive systems are increasingly chosen to offer prolonged consistent performance, Steve explains. Shell Tellus Oils contain an additive system incorporating the anti-wear additive called ZnDTP, which contains zinc and a further patented antiwear additive. According to Steve, this is a unique product: “No one else has come up with anything similar in the last few years.” This year, Shell plans to launch a new version of Tellus T, a multigrade version of the current lubricant designed for use in mobile and outdoor hydraulic systems in variable temperatures.

The Tellus range includes Tellus S, which is based on zinc free technology, and other lubricants for specialist applications, for example a detergent based hydraulic fluid.

“Generally, Shell prefers to do the technology in-house,” says Steve, “including experimental design and lab work, blending and large scale testing.” This means, he claims, that the company is not reliant on someone else’s work, and making someone else’s claims. The company also tests the lubricants in field conditions. “It’s often impossible to predict entirely how a lubricant will work in real-life conditions,” says Steve. “This is why Shell conducts field trials.”

Choosing a lubricant
So what factors should engineers take into account when choosing a lubricant? Steve mentions some of the main factors include viscosity and stability – oxidative, and hydrolytic and thermal stability. But the most important thing, according to Steve, is for engineers to consider all aspects of the lubricant before choosing it. For example, if the oil is only good in one area, such as antiwear performance, it may not be the best choice.

“It’s no use developing hydraulic fluid as an Olympic sprinter, it has to be a decathlete,” says Steve. “Falling down on one property is a disaster. So there is always a trade-off when selecting a lubricant. The engineer should have a look at several features and ask him or herself: ‘does it do several things that I need well?’ ”

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