water removal from hydraulic oil

[dho]

the big brother requires our hydraulic system contains water below 100 ppm. our semi open loop system is in an air conditioned room. we installed desiccant cartridge in the pump vent. we installed water removal filter in the return line, we just could not make the water level down below 100 ppm. yesterday test result 170 ppm. have any idea how to get it down?
thanks.

 

[btrueblood]

Heat it up and keep it heated?

 

[Compositepro]

Heating may be the best option. A filter will not remove dissolved water, only water droplets, leaving the oil saturated with dissolved water. A desiccant filter in the oil flow would work but I'm not familiar with any such products, probably because that approach may cause more problems than it fixes. Heat will cause water to move from the liquid phase to the vapor space where the vent filter-drier can capture it.

 

[MikeHalloran]

Standby generators often have electric heaters with thermostats connected to the lube oil sump, in order to keep the temperature above water's boiling point. You can buy them 'in a box', so you only have to make two oil connections to your system, e.g. in a drain line or at different elevations on the reservoir, and one electrical connection. See e.g. "Hotwatt".

Mike Halloran
Pembroke Pines, FL, USA

 

[WKTaylor]

dho...

Is 'big brother' a DoD agency, airline/cargo-carrier, smaller operator???

What is contractual rationale for this H2O level?, IE: Based on what... MM, TM, TO, NAVAIR,SAE ARP, ??

Sampling per SAE ARP598 or MM, TM, T.O.??

Have You checked the system at various sampling points, VERY CAREFULLY, to avoid introducing moisture contamination into the fluid sample?

Have You tested new hydraulic fluid to ensure it is free from moisture?

Have You tested the GSE hydraulic carts [‘mule’] for contamination? Has the customer checked their-own carts?

Does the customer check regularly check the system fluids for moisture, particulate-contamination chemical breakdown, etc… much like engine oils are lab [JOAP] tested … before sending the acft to You… or do You lab-check them as part of receiving inspection? Pre-existing contamination raises liability/contractual issues You may wish to consider. [see 'war-story' at end of this reply]

Do You service gas-pressurized components strictly with dry-nitrogen… or is there a potential that ordinary air or ‘dry-air’ was used to charge the system [IE: hydraulic reservoir, charged cylinders, etc]? Is it possible that the operator failed to use dry nitrogen?

Does the system have any entrapped air due to leakage?

What hydraulic fluid [some are more prone to moisture contamination]…???
Petroleum Base, EX: MIL-PRF-5606
Synthetic, fire resistant, EX: MIL-PRF-83282, MIL-PRF-87257
Phosphate Ester, EX: SAE AS1241
Have the petro/synth base oils been mixed, ILO, full purge/cleaning to avoid mixing

Have You considered 100% system drain purge of all oil/fluid? NOTE.
Due to multiple issues, I’ve discovered that USAF acft [older generation] rarely/if-ever have the systems fully drained, purged/cleaned, thru the jets’ lifetime.

Following document might refer to documents of interest, for further review…
SAE AIR737 Aerospace Hydraulic and Pneumatic Specifications, Standards, Recommended Practices, and Information Reports

'another Taylor war-story'
One jet I investigated in the field lost a LH inbd slat during aerial maneuvering... resulting in fragments that FOD'ed the #1 engine and damaged the inlet lip. The only pieces of the slat were fittings that appeared ‘twisted’ on the ends of (2) 'parallel' actuators. These dual separated actuators for the slat were supposed to be matched/coordinated to act simultaneously [rate of extension, thrust, etc]. However it was very obvious from a field contamination check, that one actuator system metering orifice was partially blocked with many-types of contaminates... very visible on a white coffee-filter; and 10X magnification of the orifice hole. This actuator was ‘slower’ than the adjacent actuator during both extension and retraction. The result was a serious ‘force-fight’ between the different-rate-actuators and rigid slat-tracks that twisted/bent the slat during each extension and retraction cycle... which eventually led to it tearing in-half and departing the aircraft in pieces. Records review and discussions with Acft-type the engineering staff made it painfully obvious that that the system had NEVER been drained/purged/cleaned... and the jet was +20-years old.


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[tbuelna]

The moisture in your system is likely from humidity in the air contained in the tank headspace. Installing a desiccant breather is an excellent idea. These breathers are extremely effective at removing moisture from the system, but there are a couple things to remember.

First, desiccant breathers should have one check valve that vents a small amount of moist air overboard every time the fluid heats up and the air in the headspace expands, and another check valve that allow outside air to flow back into the system after passing over the desiccant bed when the fluid cools and the air in the headspace contracts. For the desiccant breather to perform effectively the entire system needs to be tightly sealed so that air in the headspace is forced to circulate through the breather at every heating/cooling cycle.

Second, only a small volume of headspace air is exchanged at each heating/cooling cycle. So depending on the volume of headspace, and the frequency of heating/cooling cycles, it might take quite a while to thoroughly dry the air within the headspace.

Third, once the desiccant breather has functioned long enough to remove all traces of moisture, the system should never be unsealed. This would allow air containing moisture back into the system. For adding fluid you need to install a dry-break fill fitting on the tank and use a service cart with a pump so that no outside air can enter the sealed system. Even the desiccant breather system should be designed so that the filter element can be replaced without allowing unfiltered air into the system.

Lastly, it might help if you purge the tank headspace with something like dry nitrogen after the system is filled and sealed.

Hope that helps.
Terry