fluid with low oiliness

giusepperossi

Hi, I am a mechanical engineer, therefore I am no very experienced in chemistry
I need to find a fluid similar to lubrificant oil in density and viscosity, but with low oiliness
I thought to gasoline, but it is very dangerous for my aim. I have to test on the production line some components that work in oil, but I have to leave them clean
now we are using air for testing, but we have some problem. So, I think also some gases, with high density, could be ok, I thought to Xenon
thanks in advance
Giuseppe

tadchem

Without divulging any trade secrets, can you please explain what you are trying to do with this fluid? There are several families of fluids with very different properties. Compressed gases like supercritical CO2, non-polar liquids like hydrocarbons, polar liquids like acetone, hydrogen-bonding liquids like water, and ionic liquids. Properties can be changed dramatically by mixing in other materials such as salts, alkali or acid.

giusepperossi

I have to estimate the leakages of a volumetric pump. I excluded the water for the corrosion of metal. The test must be made on every component that has to go to the client, therefore the test has not to damage the pump
thanks
Giuseppe

tadchem

If the pump is for liquids, use a liquid. Gases have a way of leaking through seals that may be watertight.
To prevent corrosion, use a water-free liquid without any salts or oxygen, and dry the components after testing.
If your pump is lubricated, do not use a liquid that will remove the lubricant or attack the seals.
I suggest you consider using either the same liquid you are using as a lubricant (if you are using one) or a commercial anti-freeze based on either propylene glycol or glycerine. Both are non-corrosive and essentially non-toxic. An ethylene glycol based liquid might leave a toxic residue that customer would object to.
Be aware that leak testing is very sensitive to methodology.

giusepperossi

I know it, now we are testing the pumps with air, as our competitors also do, because the test is fast, economic and clean. But, clearly, we have some problems with this test. For this I thought also to a heavy gas.

giusepperossi

what about the oiliness of glycerol? After the test the pump has to be clean, without 'any drop' of liquid
again thanks

tadchem

Consider the price of the gas. Because of its low abundance, xenon is much more expensive than the lighter noble gases—approximate prices for the purchase of small quantities in Europe in 1999 were 10 €/L for xenon, 1 €/L for krypton, and 0.20 €/L for neon;[53] the much more plentiful argon costs less than a cent per liter. Nitrogen is even cheaper. Air compressed (and filtered) on site would be cheapest.
CO2 is sold as a bulk liquid with much lower prices.

tadchem

With that requirement, you should probably go with leak tests based on gases. Is the pump equipment lubricated with either a liquid or a dry lubricant?

With a good digital pressure gauge you can probably quantify leaks by pressurizing the system, sealing it, and tracking pressure vs time.

With a gas method you can also 'listen' for leaks using a stethoscope - or even a piece of plastic tubing with one end attached to an earpiece and the other end left open and used as an acoustic probe.

giusepperossi

This is what we are doing now with air. But it gives us much problems. The test is too much selective. We call it 'dry test'. no one lubricant is used during the test

tadchem

It sounds like you have a method that works; you just need to solve some problems it has. Just what are the problems?

Too 'selective' in what way?

giusepperossi

We discard many components. after the dry test if we test the discarded pumps in working condition we find that many of them are good. So we thought to find an alternative fluid

tadchem

It would seem that using a gas-based test method is generating too many false negatives. Theoretically, testing should be done under conditions as close as reasonably achievable to actual expected operating conditions.

Now we are at the point where an economic decision must be faced: which is more expensive, the effort and resources spent producing a product that incorrectly fails the test, or the effort and resources spent to clean and dry each unit after testing?

giusepperossi

this is the problem, my question is 'is another gas able to improve the test reliability?'
the test in working condition is not just dirty but it also very slow

tadchem

I don't think switching to another gas will reduce the number of false negatives. Even the heaviest gas (sulfur hexafluoride) will find a leak that may be too small to matter to a liquid.
Testing with a liquid will always have the problem of how does one remove the residual liquid. The more volatile the liquid, the easier it will be to remove afterwards, usually with heat and ventilation. Then you will have the problems of the vapors: are they flammable, toxic, or damaging to the environment?
Without knowing any details of your procedure I would hesitate to make any suggestions about speeding it up.

giusepperossi

I thank you for your interest, but I can't give you more details. However I have 5 months for working about this problem.

giusepperossi

Just a question. If I have a liquid with low superficial tension, does it wet the metal less the metal than ones that has an high superficial tension?