foaming in hydraulic oils(URGENT)

Hydraulic oil can contain as much as 9% air and be considered normal although LESS is better. That is why efforts are made to eliminate air entrainment and all oils will have a air release property and number assigned. Abnormal amounts of air can usually be traced to loose piping on the suction side of a pump, leaking pump shaft seal or lines coming into the tank that are terminated ABOVE the fluid level or running an extremely low tank level. This is not to say that these are the only sources just the most common. Personally I have never run across a faulty oil. If you need more specific help you can contact me at

generalfluidpower@yahoo.com

Tom

Can you specify the limits ie the acceptable foaming sequence values.

If you are asking about ASTM D-892 Foam Tendency &stability Limits It is 50/0 For the three sequences

thanks fageer....

quote:

Originally posted by fageer abdalla:
If you are asking about ASTM D-892 Foam Tendency &stability Limits It is 50/0 For the three sequences

This limit may be valid only as a requirement for new oils you are trying to buy. Once the oil has been in service for a while foaming numbers do clime up due to contamination (dirt, varnish, wear, etc.) or cross contamination with another lubricant and/or additives.

Limits, condemning and/or warning, should be set based on each particular application. Many used oils with foaming numbers five times higher than the numbers mentioned by “fageer” are performing satisfactorily. Foaming characteristics are usually improved by better conditioning of oils (fine filtration and demoisturizing).

Perhaps you should get concerned if you have more than an inch foam floating in the tank. Also look if the foam stays or breaks down and new foam is formed from the bottom. That will give you a hint about the source of the foaming oil.

Agree with John that the test limits apply for new oil. Oils in service may have worse values due to contaminants.

As previously pointed out, foaming can be related to aged oil, dirt or excessive water contamination or contamination with another oil type that contains detergents.
Have you had the oil tested?
Sometimes the oil may foam whilst in service and not when performing the foam test (ASTM D892) - this may hint to a system induced foam rather than an issue with the oil.
Has anything been changed in the system or any repairs carried out?

Hardy,
Updates, did you get your problem resolved?
Tom

Foaming is also a result of excessive contamination by contaminants that are under one micron, below normal static filtration capability. We found that using our systems to reduce this contamination, not only results in better oil chemistry, but also elimination of foam. Our agent in Southeast Asia, Andy Sitton has done some experiments to determine the effect of submicron contamination on air release and found the numbers improve dramatically when this contamination is reduced. We have also seen quit a lot of anecdotal evidence of this on the machines that have ISOPur systems. They stop foaming!

i agree that according if you testing the oils as per ASTM D 892.50/0 at any sequence should be only applicale for fresh oils .

So what do you think is the limmits for foaming in inservice oils.Both hydraulic and engine oils ...

Can faoming be due to the poor air release value of the oil??

Dear Hardy,

Foaming ASTM D892, air release D3427, inter facial tension, and demulsibility D2711 are all surface properties and therefore all generally related. As you so aptly quote the 50/0 result for foaming tendency / stability is only a real benchmark for new oil. Your oil analysis lab may give you some good guidelines for the equipment you are operating but this will depend on the Oil type, Temperature of operation, Air leaks in the system, and plunging return lines into the tank. Cllct your data and then call the lab and the oil supplier for help here. Too many variables for a blog.

Good luck

D892, D 3427, D 1401, & D 2711 are all bench tests. They have their value and I've put dinner on the table running all of those and more, but the most important test for you is not in some used oil lab, it is in your system.
Here is the first question you have to ask yourself: Is it foam (above the surface) or air entrainment (sub-surface)? If you open the reservoir lid & see it on the top, that's foam. If you see it in a sight-glass, that's probably air entrainment. Given a choice, I'd take foam; air entrainment is much worse.
We'll assume it's foam. The next question: Is it a cosmetic problem or a real problem? Do you have a little layer of foam on top of the reservoir, or is it foaming out of the breather and creating a safety hazard? If the problem is cosmetic, ignore it.
If it's real, the first thing to look for are mechanical causes. If the reservoir level is low and the return line is above the surface and creating agitation, just topping up the reservoir might solve the problem. Has a pump been swapped out recently? Are the fittings nice & tight on the suction side? Sucking air into the pump will cause foam if you're lucky, air entrainment if you're not.
If you come up empty on mechanical causes, then your foam properties have degraded. It's less common, but I've seen it often enough. It is usually caused by contamination. Fine particulates are a frequent cause. Gear boxes in a cement mills are very prone to this. Some like to top-treat with silicone, but overtreating for foam can cause air entrainment. Also, top treating doesn't address the root cause. I'd check the breather or any other place that dust can get into the system, then change the oil at the next opportunity

Dear Hardy,

If you experience foam,the anti foam additive may have depleted. Unfortunately, tank side additive are short term solutions.

The best way to break the surface tension or "kill bubble build up." This can be done by laying a netting in the tank, at level with fluid level.

Hussam