I got this question from a Hydraulics Pro Club member:
"We have experienced Micro Biological Contamination (MBC) in marine fuel oil systems for several years but we are starting to see MBC in marine hydraulic systems. This can be very bad news for hydraulic systems. How can we prevent it?"
Micro biological or microbial contamination is basically the growth and colonization of bacteria in the oil. And as is the case with all organisms, these bacteria require certain conditions to survive and grow:
- Water: emulsified in the oil, 500 ppm (0.5 ml per liter of oil) is sufficient.
- Food: carbon, nitrogen and phosphorous, readily supplied by the oil.
- Oxygen: air is typically present in hydraulic oil at 7% to 10% by volume.
- Optimum temperatures: 24°C to 49°C (75°F to 120°F).
- Dark, stagnant or low flow areas: i.e. the reservoir in hydraulic systems.
- Suspended particles: assist with initial transportation and colonization.
While all of the above ingredients are required to sustain bacterial growth, water is the key. And this gives us a clue as to why this member is seeing it frequently in marine hydraulic systems. They are more susceptible to water contamination.
So in terms of prevention, keeping the oil dry is a biggy. Another operating factor which can be influenced without too much difficulty is operating temperature. Just as with the storage of food, we all know to prevent the growth of bugs, food should be stored at a low temperature in the refrigerator or kept hot at high temperatures.
A hydraulic system operating temperature above 50°C will similarly prevent the survival and growth of bacteria. But if you've been reading my stuff for a while, this advice may appear to go against the grain. After all, I'm a big advocate of decreasing hydraulic system operating temperatures, NOT increasing them. That said, it's all about the degree - literally. Matched with the correct viscosity oil, 50°C to 65°C is not an operating temperature of a magnitude which is going to cause other reliability issues.
A third preventative factor, and something which is really hydraulic equipment reliability '101', is the maintenance of low particle counts in the oil. Bacteria need water to grow, but they also need a host on which to coalesce and start a colony.
Put simply, the key to preventing a whole host of hydraulic problems, including this one, is to keep the oil DRY, CLEAN and COOL. The 'cool' part is relative term. Compared to 85°C, 50°C is cool. But as you can see, allowing the hydraulic oil to run wet and warm is a mistake. Because it's the perfect environment for bugs to grow. And to discover six other costly mistakes you want to be sure to avoid, get "Six Costly Mistakes Most Hydraulics Users Make... And How You Can Avoid Them!" available for FREE download here.