Which oil or grease will work the best?

[EdDanzer]

We are building an air amplifier for a customer that runs 24 hours a day 7 days a week in an environment that has temperature variations from 0°F to 150°F. This unit pumps 450 psi air, which generates temperatures of about 400°F at the high pressure seal. Our original testing was done with Chevron Supreme 30 Wt motor oil wiped on the seals and bearings. The unit ran 1.2 million cycles, and was dissembled. The Viton high pressure seals and the filled nylon bearing showed significant wear and little oil was left. There was evidence of varnish and carbon at the top of the high pressure barrel. We assumed the oil was burning. The low pressure urethane seals and filled nylon bearing showed little wear and still had oil present.
A group decision was made to use Dow 111 grease, used by another pneumatic valve manufacture, this grease migrated into other areas and caused a functional failure.
The customer wants us to use Mobil DTE oil or Magnalube-g, a grease. We would like to use a 2 stroke motor oil. Our thoughts on choosing the 2 stroke oil is, clean burning, low varnishing, good high temperature stability, and will not cause functional failures if it migrates out of the area needing lubrication.
Our customer is concerned with the detergents in motor oils causing seal failures.
Please give reasons to support any of these lubricants, of suggest another.

Thanks in advance,
Ed Danzer

 

[rudyhiebert]

Ed:
I believe that synthetic will work the best. If you are interested in using Amsoil, email the Technical Dept. at tech@amsoil.com and I'm sure somone there will give the credentialed reply you are looking for. (I'm at

http://www.lubedealer.com/hiebert

if you need it)

 

[Xtrema]

My first reaction was surprise that one nylon-filled bearing wore and the other didn't. Are the bearings sufficient for the applied loads at the high temperature zone?

400 F for any sump oil is quite high. Varnish and carbon are sure signs of oil oxidation.

A custom lubricant might be in order. As previously suggested, synthetic base stocks outperform mineral oils at these high temperatures. However, the additives in motor oil or grease may be unnecessary for the air amplifier and you may create problems. One very capable grease manufacturer is William F Nye. (No, I don't work for Nye.)

It is interesting that one air amplifier manufacturer, Haskel, notes that they don't use lubricants!

 

[EdDanzer]

The reason we have built this is to replace the Haskel, and others. Our customer spent several years trying to get Haskel and other manufactures units to work in this application. We have found grease gets sticker with time and temperature, oils varnish and carbonize. The air valve spool comes with grease and should run without further lubrication, but does not. There is ongoing experimentation with small amounts of motor oil lubrication in the air for all moving components, and this seems to be the best solution so far. One other note, these units are used world wide, so motor oil is a locally available product, and has a better chance of being applied correctly.

 

[Xtrema]

I like your approach of a single low viscosity motor oil. With regard to your 2-stroke oil idea, Bel-Ray makes great motorcycle oil. I don't know if they distribute worldwide.

 

[patprimmer]

Ed

I can supply info on a 85% bronze filled nylon that might eliminate the need for oil, but I am commercially involved with it's manufacture and supply, so I should not use this site for promotion.

If you need more info contact me directly

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[EdDanzer]

Pat,
Your material is interesting, but the air valve must be lubricated and the people we have designed this for don’t want to do anymore material experimentation. We tried a bronze filled Teflon seal and it failed quickly.
But for other projects please send material information to ed@danzcoinc.com

 

[Xtrema]

Regarding a special lubricant, you might consider a hybrid approach. Use a widely-available lubricant, purchased on site. Send a small quantity of an additive known as "anti-oxidant" for the end user to blend with the standard lubricant. The quantity of anti-oxidant needed will be so small (0.05 to 0.10 weight percent) that a very small tube would treat many amplifiers. The anti-oxidant boost might effectively delay the degradation of your fluid at 400 F.

 

[Tmoose]

Is your role is to develop the best design, or strictly to determine the best lubrication?

If my role was lube only, I'd be thinking that at one time garden variety ATF had some pretty impressive hi-temp characteristics compared to motor oil of the same vintage. The Turbo era may have changed that. I'd guess Mobil synthetic ATF might be the high mark.
I'd also call Kluber.

http://kluberna.com/

I'd drip a little DTE , few regular and synthetic motor oils and ATFs on an aluminum plate at 400, 500, and 600 F to see where they smoke and char.

Sure would be nice to be able to cool that area off a bit.
With compressed air close by maybe some would be available for cooling.

I have little love for "bronze" as a bearing. In order to make it survive in marginal lube conditions the recipe has to be chock full of lead. It expands when hot, so when mounted in a substantial housing the ID shrinks and grabs the spinning shaft "until the sparkles come out."

 

[EdDanzer]

We need a world wide off shelf available lubricant, so my need is to determine the best possible solution with those constraints. Originally the unit would be lubricated once at assembly. The problem is the 150° F air coming into the unit removes most of the oil and grease causing the air valve to stop shifting. When the 150° F air is compressed to 400 psi the temperature will rise to over 400° F.
The current operation is to inject a small amount of motor oil in the air stream. It will be several months before more details are available.

 

[s13sr20chris]

would periodic maintenance be out of the question? the major components of atf seem to survive very high temperatures but it is higher in detergents than motor oil. i have actually tested auto exhaust systems for leaks by running atf into the intake manifold. with no leaks it will come out of the tail pipe in a puddle.

 

[EdDanzer]

Everyone has resigned them selves to periodic maintenance. ATF was considered, but with a lower viscosity, similar to turbine oils not used. During testing the lower viscosity oils seemed to blow away faster than the higher viscosity oils. I suggested gear oil, but the oiler’s don’t like too thick of fluids either.

 

[Tmoose]

"Our customer is concerned with the detergents in motor oils causing seal failures."

Is she worried about the Viton seal? I think Viton will explain they have no fear of motor oil.

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Is there a way to run another line to apply minimal oil to the seal directly? Or are ther other areas that need the bulk oil ?

 

[EdDanzer]

The person who was concerned with the detergents is no longer with the company. Viton U-seals did not perform well in the long run. The best piston seal so far is a glass filled Teflon. The areas that need lubrication are reciprocating parts and there is no way to just lube the seals other than with oil in the air.