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Old 04-12-2010, 04:14 AM   #1
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Join Date: Oct 2007
Posts: 14,908
Hydraulic Malaise

Found a really unique (to me at least) problem on the SSCA board.

While most of these folks are offshore sailing cruisers , a few share the steering common on "trawlery" sized motor boats.

As copied and pasted,,

"I have recently experienced a couple of instances of the hydraulic clutch valve sticking on my Raymarine hydraulic autopilot. I've taken the valve out and cleaned it and it works fine in bench testing. I reinstalled it and it wasn't long before it stuck again. Sometimes it sticks in standby and sometimes in auto. In any event, I have found the fluid in the reservoir to be very dirty and the only plausible explanation I can come up with is microbial contamination. The system is only two years old and the fluid and reservoir were pristine on installation. In the two years it has been installed, I've not had to add any hydraulic fluid, so there aren't any appreciable leaks. The reservoir is, of course, vented, so I am theorizing that atmospheric humidity led to enough water in the fluid to support microbial growth. I have drained the fluid and cleaned out all the grunge from the reservoir and am thinking of flushing the system a few times with Biobor-JF.

Has anyone experienced, or heard of, microbial contamination in hydraulic systems, or heard any discussion of adding a biocide to a hydraulic system? Any feedback would be appreciated.

Most probable is a fungal contamination.

Fungal contamination is common in systems containing fuel oil, hydraulic oils, dielectric insulating oils, etc. The fungal species involved are 'resin formers', using the 'oil' as its nutrient source with or without the presence of water (vapor) absorption into the prior dehydrated fluid. Do websearch for Cladosporium Resinae - "kerosene fungus", etc.

Such contamination can be mitigated by using a 'bio-blocking' filter element on the vent. However, that implies that the system is 'sanitary' and already free from contamination. Typically such ingressing fungal spores are aspirated from the atmosphere and can be retained on a filter membrane of at least 3,0M (abs. - 100% eff.). Nowadays, a simple bio-blocking hydrophobic PTFE membrane (capsule filter) of 0,2M (liquid rating) is the most commonly (cheapest) used to filter the VENT. Such would be available from such manufacturers as: Pall Corp (Aeropower div.), Parker Advanced Filtration (Parker Hannefin / Racor Div.), Millipore Corp. Pall Aeropower also is involved in the manufacture of porous stainless steel filters for debris removal IN the hydraulic lines - but can require precise and intense maintenance. For all of this, the system must be reestablished as CLEAN and SANITIZED.

For a 'plain vanilla' remedy, go to a local hydraulic equipment distributor who specializes in AIRCRAFT and ELECTRIC POWER GENERATION applications. For the BEST probable remediator, choose a Parker Hannefin ( hydraulics distributor - and then advise them of the application of a small PTFE *VENT filter* from Parker Advanced Filtration Div.
I doubt that Raymarine will be of much help other than to list the sealing materials so you can further select a compatible bio-cide if that is your choice - the elastomer seals of the system MUST be chemically compatible with any biocide compound - very tricky and very 'chancy'.

If it were my system, I'd thoroughly clean it out; install a porous stainless steel membrane 1,0-5,0M filter on the discharge of the pump (with differential pressure gage across the filter and wired to an alarm); block and bypass 'around' the inline filter; NEW oil; a 50mm 0,2M (100% eff.) PTFE filter on the 'vent'.

Great info , should anyone suffer this malaise.

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