MIL PRF 5606 foam contamination 1

[FranAle]

Hi everybody

A 3000 psi hydraulic system of an aircraft don´t pass the test for foam occurrence (max 60 ml under certain crcunstances for testing) My company spent time and many MIL PRF 5606 drums trying to figure out what is happening. We covered several issues related like temperature, cavitation on pipes, drums storage, enviromental controls and we have no answer about this problem(it may be no problem, we don´t know).
During maintenance work, we haven´t discovered any pipe wear,leaking or squak relate to it in all the 20 aircraft of the fleet and for almost 2 years. The labs always replay
"your samples don´t pass the foam testing"
We are trying to answer questions like:
Why or what produce the foam on the liquid?
Can this test be only a labs trick?
What else can we do?
We are open to any clues, thanks.

Francis

 

[aviat]

MIL-PRF-5606 calls for ASTM D892 standard for checking for foaming. I looked up in the 02 edition and under section 10.5 it explains your situation. It says that with modern additives lubricants can pass foam requirements when blended, but fails after being stored for two weeks. However if the lubricant is poured into engine, transmission, or gearbox and then operated for a few minutes if will return to its blended requirement. In other words you could send a sample that has not been in the A/C and it would not pass. It goes on to explain why and explains that the testing agency is to put a sample in a blender and agitate it before doing the test. It could be that they are not doing this step.

Another problem could occur with sampling methods. Sample should be taken as soon as possible after flight, or if in maintenance, the system should be operated by hydraulic cart or pumps until at operating temperature all the while operating landing gear or other components in the system, before taking sample. Then put date on sample bottle and in records and sent to lab ASAP, and if lab. report comes back with date more than two weeks after the date taken, you would know that it is not reliable as per above.

 

[FranAle]

Hi Aviat

Thanks for your comments. I'll let you know our findings when we track more samples with your approach.

Francis

 

[FranAle]

Aviat

We made tracking for oil hydraulics samples and correlated samples taken directly from aircraft, after landing and others taken from the same A/C with no engine running and guess.
Lab was cheating us because they were using the method for ASTM D 892 as they think it may.
We changed lab survey, and since then samples are passing the tests just fine.
Thank again.

Francis

Francis