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Interval between Gear Box Oil Replacement

Interval between Gear Box Oil Replacement

Interval between Gear Box Oil Replacement

The gearbox oil replacement for the EVAPCO cooling tower was tested by a reputable lab, and the parameters were found to be within the limits. But the gearbox's nameplate says that the oil should be changed every 2500 hours. Should I follow what the manufacturer says or what the lab says?

The problem with the world is that intelligent people are full of doubts, while stupid ones are full of confidence.
-Charles Bukowski-

RE: Interval between Gear Box Oil Replacement

Hi moideen

If it were me I would change the oil as suggested by the manufacturer.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

RE: Interval between Gear Box Oil Replacement

Did you do an infrared Fourier spectrum analysis? If not, you do not know the condition of the EP oil additives and lack the required information to determine the condition of the oil for continued service.

RE: Interval between Gear Box Oil Replacement


who does the test

RE: Interval between Gear Box Oil Replacement

Herguth Laboratories, now SGS


The mass spectrometer testing only tells if elements such as zinc and phosphorus are in the oil. It doesn't tell what compound they are in. As the oil wears, compounds such as ZDDP can break down. This doesn't cause the mass spectrometer reading to change but does result in a loss of lubricating properties. The IR Fourier spectrum analysis compares old oil to new to quantify how much the oil has changed. It's an expensive test to run as it requires two samples be run initially. Herguth does have a growing database of lube oils so you might get lucky.

RE: Interval between Gear Box Oil Replacement

I've always liked this info from Flender -

RE: Interval between Gear Box Oil Replacement

Personally, I think a 2500 hour change interval is obnoxious. Most manufacturers do allow double change intervals if the PAO oil dik mentioned is used. Is this a worm drive speed increaser? That's the only machine I see with such a short interval.

RE: Interval between Gear Box Oil Replacement

Thank you for all of your input. @TugboatEng: Thank you for informing me about this oil testing procedure, IR Fourier spectrum analysis. In the lab, just three characteristics are measured: viscosity, total acid number, and water content. For a long time, the same characteristics have been frequently monitored in our business, regardless of whether the application is small or large. The cooling tower in question has a total refrigeration capacity of 10,000 tons. As a result, according to the manufacturer's recommendations, regular oil changes are critical.

RE: Interval between Gear Box Oil Replacement

Oil analysis is a powerful tool if used correctly but as used generally is a tool to fool auditors.

RE: Interval between Gear Box Oil Replacement

The oil change frequency will depend on the type of oil and the "load" on the oil during use. That means that frequencies given by the manufacturer are just a figure to start with - in practice the useful life of the oil might be lower or larger depending on operating conditions.

In this particular case a rather simple R&O oil is recommended - a oil that gives protection against rust and oxidation but normally does not contain anti wear or EP additives.

In practice the allowable change interval will depend on the operating conditions and can be both shorter and longer then recommended. Usually gear manufacturers are rather prudent with their recommendations because they cannot always foresee what the operating conditions are in a particular situation.

If you want to base your oil change interval on lube oil analysis, there are are a few things that need to be checked: viscosity, TAN, water content, wear elements, FTIR analysis and maybe a cleanliness test. Ingress of water in the lubricant should be avoided if at all possible, since it may lead to higher wear, corrosion and because it works as a catalyst on oil oxidation.

The generation of iron and steel wear metals in gears is unavoidable, but the harm they can do can be kept in check by incorporating a magnetic element in the reservoir preventing continuous circulation to a large extend. It thus pays to keep the oil "dry and clean".

The oil itself can "wear" also: especially at higher operating temperatures parts of the oil may be prone to oxidation, which can result in oil thickening, darkening of the oil and the forming of deposits (lacquer) and sludge(oxidised oil mixed with water).

The analysis figures reported do not indicate that the oil needs to be changed. But if you want some more information on the condition of the oil and whether a oil change is recommended some additional testing may be appropriate. You better discuss the matter with the lab that does the analysing to find out what additional testing might be useful in your particular case.

RE: Interval between Gear Box Oil Replacement

Gearboxes that live in the steam inside a cooling tower are very vulnerable to water contamination and subsequent gear and bearing failure.

Some oils brag that they do not absorb water, by resisting emulsion formation.
In my mind that may not be such a good thing if all the water that falls out of suspension does not collect safely in a sump that can be drained.

I've seen some gearboxes that go to great lengths to provide oil to bearings by adding troughs and scoops to collect oil flung from the gears. There were some fairly quick failures, and it was fairly obvious that over time the bearings were getting a dose of water dutifully collected by the oiling "system." To make matters worse, changing those gearbox's oil would not drain the water collected near the bearings.

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