dark hydraulic oil.

Generally return filters will be in the 10-25 micron range-this is my experience in heavy industrial applications. Going to a finer micron will increase the back pressure and possibly go into a "bypass" condition. The finer micron filter might be acceptable if it was used for a
"polishing or kidney loop". You may have more trouble than just particulates with the discolored
oil(oil oxidation) but your lab report should pick up on that condition if it exists.
Hope this helps, if you need more specific info you can contact me via email

generalfluidpower@yahoo.com

Tom

Dear Chutzy,

Hydraulic oils that become dark in usage indicate oxidation and which is normal. If however this happens within a few hours it could probably be "dieseling."

In many systems that work under very high pressure or temperature the oil molecules get "burned" this is called dieseling. This could happen in die casting machines, injection molding machines etc.

One way out is to use very high VI oils ( 130 plus VI) or synthetic hydraulic oils. The final option is to increase surface area of the body of oil to dissipate the heat; which means doubling or tripling the hydraulic oil sump/capacity.

Hussam

What is the application of your hydraulic system? Are youhaving issues with short filter life or sticky valves?

Dear Chutzy,

Dark oils indicate that the oil is dark, and must be put in perspective.

How many hours has the equipment been operating with this oil.
• 
  Is there a hot-spot in the system where the oil is overheated causing Coakeing.
  Is the level in the reservoir low allowing air to recirculate into the pump intake causing dieseling?
• 
  Is there a good air filtration system on the tank breather, Pollen and dust can cause dark oils.
• 
  If the oil has several hundred hours of operation and the oil is more than one year old the solution may be to change the oil.
• 
  Is oil analysis available detailing the type and level of contamination present.
  Have you determined if water is present in the oil, and if so, how much?
• 
  Try to quantify the contaminants and then return for solutions.

Remember that return filters are designed to capture large particles which if recirculated would cause immediate catastrophic harm. For the removal of fine contaminants use a kidney loop filter with a depth media. Look on-line for companies to help.

quote:

Dark oils indicate that the oil is dark

There is one of the very few definitive statements I can support.

A color change is a good reason to be alert, but a poor reason to run around with your hair on fire (until you know why it's dark, or even IF it's dark, as the original poster appears uncertain as of yet).

There are two additional potential causes of oil darkening, both rather benign:
Amine antioxidants will darken significantly under some circumstances. Antioxidants will react as they do their job, frequently producing reaction products that give you colors ranging from a brilliant yellow through a deep red to an inky black, depending on a number of factors that include formulation, operating conditions and any contamination that may be present. While it may look scary, these reacted species still retain considerable antioxidant potential, since they go through a series of these reactions before becoming truly exhausted.

The other cause is perception. A certain amount of color change is inevitable in service, but some people are more easily freaked out. I had a frantic phone call from a sales guy because a customer had seen a color change among drums from the same shipment. He had provided me label info, so I knew the shipment included drums from at least two batches. I walked over to the lab to get a look when they arrived. I asked where they were and was pointed at two samples of pale yellow oil. On the lab bench, they looked identical. When I held them up to the light, one was just barely darker (or was it the other one?) Run basic analyses and cut-and-paste my boilerplate statement about normal batch-to-batch variation. Oh yeah, a phone call to the sales guy telling him we'd rather not see any more "cardiac" samples from this customer unless he's actually visited the location and confirmed that there really is something going on.

The first question to ask when you observe a physical phenomenon related to the oil:
Are there any operating changes? These can be filter-plugging, oil temperature or pressure changes, foaming, a REAL viscosity change (not measured by the Eyeball Viscometer) or other abnormal behavior. If the only thing that has changed is the color, it bears watching, it may merit analysis, but I'd avoid shutting the operation down on the basis of a color change alone.

Hi Chutzy
As mentioned above Dark Oil on its own should be investigated.
If you can see particles then complete a patch test and if significant the dirt and debris will be deposited on the patch.
Check if normal oil testing is being completed as significant fluid damage should be shown in Oxidation, TAN and particle count.

To filter out would require specialised towel roll type filters as a bypass unit polishing the fluid but the reason why the lubricant has darkened should be checked.
regards

Rob S


rttech.com.au

Hello,

first thing to do is to get an oil analyse.
If the oil is dark it doesnt say that it is contaminated with particles.
Sometimes the oil gets dark by overheating or chemical attack.

So if you got the analyses you can say exactly
what is wrong. To much particles and or water ? then go for a radial microfilter.

It will take out both and the oil will get lighter (but not like new oil)

Also check chemical stability of the oil.

If you like send the analyses and i'll chekc them out for you.

also you can contact these specialists in Bogota:

Ecofiltros de Colombia S.A.

Ave. 15 # 119 - 43 Of. 501
Bogotá, D.C. Colombia


Phone : 2142204
Celular :
31057767772

E-mail : contacto@ecofiltros.net


Good luck

Martin

quote:

Originally posted by Chutzy:
Working on a hydraulic system and the oil is very dark or cloudy particulates seem to be passing through the return filters. Does anybody know if there is a additive to help remove the particles. Also what is the smallest micron filter that could be installed to help remove the material. Particulates may possibly be burnt hose or decomposed rubber material. Samples are on the way.

Dark hydraulic oil is a sign of oxyidation and contaminstion. In circulating systems, hydraulic oil can be subjected to long periods of time in oxidizing conditions such as high temperatures, relatively high surface exposure to air and metallic catalysts. Water often enters systems by fluid leakage or condensation from the reservoir breather pipe and even small amounts of water will cause rusting of ferrous surfaces. Circulating oils are subjected to conditions which make them liable to foam or to retain minute bubbles of air in fine suspension.
thanks
regards,
Dave