We have 4 Sullair industrial oil flooded rotary screw compressors in our plant, 250hp, prolly 800-1000 SCFM each, radiator oil coolers, synthetic oil, close to twenty years in service. I've been told they are about 10 years over life expectancy (plant legend?).
Yearly maintenance is oil change (about 55 gallons ea.), air inlet and oil separator filters, main and secondary oil filters, radiator cleaning. Mostly trouble-free, maybe a mid year primary or secondary oil filter change per pressure differential only. Last maintenance service was Jan./ Feb.
Each compressor has had at least one secondary oil filter develop a pin hole in the bottom of the bowl. Two have had two filters replaced w/ pinholes since Jan./ Feb. service. Filters are steel shell spin-on type similar to automotive oil filters and about the size of an old HD truck oil filter. No primary filters have been replaced yet.
I cut one old pinhole leaking filter open and found rust looking particles laying in the bottom of the bowl. Wiped out the bowl and there was small pitting w/ corrosion in the pits. The next filter I cut open had the same rust looking particles w/ some rust looking flakes. After wiping out the bowl there were about 10 pits 3/32"- 1/8" size but no corrosion in the pits... it was like clean metal. My first thought was acid. Latest filter cut open had the same small pits w/ corrosion as the first one, did find a couple beads of moisture in the bowl.
I'm still sticking w/ the acid theory. Boss said maybe a bad batch of filters. Also, the particles/ sludge could trap moisture below the oil and corrode. I finally convinced the boss to get oil analysis done, still waiting on results.
What I find extremely odd is all four units having the same problem starting at the same time, I could see maybe one developing this problem, all four is too much. I was off on sick leave during the last compressor service but have to assume all service was done as usual. AFAIK nothing else has changed, same inlet air intake, all running normal temps and pressure differentials, no mechanical problems.
One compressor engineering site says not removing all the oil per oil change may lead to high acid content (LAN). Leaving an estimated 5-10% used oil in the system oil change after oil change, year after year will progressively shorten the planned yearly oil life to months... this makes the most sense to me. If the filters are corroding this bad WTF is happening to the gears, screws and bearings...
What ye say GRM braintrust, what am I missing here? I'm baffled. We need to keep these units running, I'm thinkin' this company ain't gonna drop off the old bag-o-money for new compressors.
