Troubleshooting: Oil Carryover

Oil showing up downstream is an expensive problem. It ruins paint jobs, contaminates product, swells some seals, and fouls dryers and filters. First find out where the oil is coming from. Sometimes it is the compressor. Sometimes it is a lubricator someone turned all the way up.

Symptoms the customer will describe

• Oily film at blow guns, tool exhaust, or on parts
• Downstream filters soaked or bowls holding oil
• Desiccant dryer losing performance (oil coats the desiccant)
• Oily condensate at drains
• Compressor oil level dropping faster than normal

Likely causes, most common first

1. Point-of-use lubricator set too high. Check this first if oil appears at one machine and not across the plant.
2. Separator element failed or saturated (lubricated rotary screw). It is a service part with a life. Past that life, oil gets through.
3. Oil overfilled. Too much oil in the sump floods the separator.
4. Scavenge line plugged. The small line that returns oil from the separator to the sump is blocked, often at a strainer or orifice. Oil builds up in the separator and carries over.
5. Running at too low a pressure, or a failed minimum pressure valve. Lower pressure means faster air through the separator, and more oil carried with it.
6. Wrong oil, foaming, or overheating. See the high discharge temperature guide.
7. Piston units: worn rings, overfilled crankcase, or running past the duty rating.
8. No coalescing filter where the application needs oil-free air. Every lubricated compressor passes some oil. The maker’s carryover spec tells you how much.

Quick checks a rep can do on the phone

1. “Is the oil everywhere, or at one station?” One station points to a lubricator or that machine.
2. “When was the separator element last changed? How many hours?”
3. “What does the sight glass show? Who topped it off last, and with what?”
4. “How fast is the compressor using oil? Has that changed?”
5. “What pressure does the compressor run at? Did someone lower it a lot?”
6. “Is there a coalescing filter after the compressor? When was the element changed?”

Fixes

• Set lubricators to the tool maker’s rate, or remove them for non-lube components.
• Replace the separator element on the maker’s schedule.
• Drain oil to the correct level. Use only the specified lubricant.
• Clean or replace the scavenge line strainer and orifice.
• Restore normal operating pressure, or replace a failed minimum pressure valve.
• Add or service coalescing filtration. Add activated carbon if the application cannot tolerate oil vapor or odor.
• After the source is fixed, clean or replace oil-soaked filter elements and desiccant. Old pipe can keep shedding oil for a while.

What to quote

• Separator elements and compressor maintenance kits
• Compressor lubricant to the maker’s specification
• Coalescing filters and replacement elements
• Activated carbon filters for oil vapor and odor
• Lubricator adjustment parts, or non-lube FRLs where components allow
• Oil-water separator for condensate
• Replacement desiccant, if the dryer was contaminated

When to escalate

If the customer needs oil-free air to a specified class, get the ISO 8573-1 oil class in writing. Class 1 allows 0.01 mg/m³ of total oil. That is a filtration design question, not a single filter pick. Bring in the filter or compressor maker.

Sources

1. ISO 8573-1:2010, Compressed air: Part 1: Contaminants and purity classes (oil Class 1 limit of 0.01 mg/m³ total oil, including aerosol, liquid, and vapor).
2. DOE/Compressed Air Challenge, Improving Compressed Air System Performance, 3rd ed. (lubricant carryover in lubricant-injected compressors; filtration and coalescing filter placement; condensate treatment).
3. Compressor maker service manuals (separator element life, scavenge line, minimum pressure valve, oil level). Carryover specs and service intervals vary by model; use the maker’s figures.