A customer recentlt asked me to examine a oil sample taken from a hydraulic test stand.At first sight the oil appeared discoloured and i thought water might be present. After further investigation a sample taken from the tank floor contained a fungus like contamination.The unit had been sampled approximately three months ago and no contaminant was apparent. the unit is run only once or perhaps twice a week and is situated indoors.Could the infrequency of operation be a factor in the build up of this bacterial growth?

Bacteria needs 2 things to survive, water and food (oil). Bacteria is everywhere. The bacteria that concerns us oil folks is in the air on particles. All it takes is for a particle to get sucked into the oil reservoir and have some moisture (preferable free water) and the stuff begins to grow at a rapid rate. It will appear as a black slime on the walls of your tank. Hope this helps.