Hydraulic And Lube Oils

Good Question. I have wondered about this myself. The best respondents will be people with years of machining experience, whom, alas are a diminishing group here in the U.S, with no one to pass their skills to. I am interested to see what they have to say.

Hands on experience of an individual is the biggest asset in diagnosing the maintenance problems in machines. Though manufactures recommend oil changing with specific duration of working. Many times I have observed experienced machinist by physical inspection and touching the oil decide the need for replacement of oil. Experience is a good teacher.

Hydraulic oil absorbs moisture rather easily, to test for water, take a half filled test tube and heat it over a gas flame, if it starts to "crackle" as a deep fat pan does when chips are made, thats water.......

How much and how long it crackles depends upon the amounts of water and the amounts of heat......but we were taught that ANY indication of water in this manner means that the oil needs replacing......

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The single major difference between normal lubricating oils and synthetic oils is that the normal oil if overheated makes carbon, which can damage bearings, blocks oil-ways and sits on other components in a car engine for example.

Whereas Synthetic oil just evaporates.

I hope this fits in with your queries.

In general, I would say that hydraulic oils are among the least complicated lube oils used in industry. A good quality hydraulic, new should have an ASTM color <1.0. After use, assuming a normal oil change cycle, the color may be in the 3.0 range. The color change is primarily caused by oxidation. One thread noted water present and a simple test which, if you have the test tube etc. would work ok. For a hydraulic system, one wants to protect the hydraulic pump. The additives present in hydraulic, often called Anti-Wear do a good job in this regard. But, they do wear out due to thermal oxidation and this is what will determine (along with excess water) the time to change the hydraulic fluid. Also, if the fluid is not bright & clear, this would be a visual indication that something has contaminated the fluid. Many operators send their oil samples to a lab that specializes in analyzing all kinds of fluids and can detect wear metals for preventive maintenance.

While some degree of the fluids health can be observed visually, the best method is to send it to a testing lab. I probably did not answer your question very well, sorry for that.

There are a few the most important oil features which should be monitored and it does not matter if we are talking about hydraulic oil or the lubrication one.

These are:

- viscosity,

- TAN number,

- moisture,

- clean class (NAS or ISO or SAE),

Oil manufacturers and OEMs of systems and devices which include oils as the working liquids usually give the limits of the oil features mentioned above so it is easy to define when the oils should be changed to the new one.

The changes of the oil features when monitored regularly, can reveal some oil systems weaknesses, so we can act to avoid the development of deterioration. It is possible to improve the oil quality using filtration. Additionally the oil life can be extended when a proper maintenance is in place.

What I have written above is applicable mainly to steam turbines oil systems but can be common for other systems as well , I think. Please correct me if I am wrong,

The basic tests used to have an idea what is the oils conditions are:

- oil colour assesment (would be good the know what was the colour of the new oil),

- oil transparency,

- oil smell,

All of above are very subjective (especially when 30% of men have the problem to name the right colour :-)). Anyway it is possible to have some idea about oil and its system , using them