During a walk-through audit, a compressed air auditor noticed a pail collecting lubricant from a filter drain. The pail was almost completely full, causing the auditor some concern. He knew that this was a sign of several possible problems.
High oil or lubricant accumulation downstream of a lubricated screw compressor is often caused by issues with the oil separator, operating conditions, or maintenance practices. One of the most common reasons is a failed or saturated oil separator element, which allows excess oil to pass through instead of being properly removed. Using an incorrect or poor-quality separator can also reduce efficiency, leading to higher oil carryover. Additionally, high air velocity caused by running the compressor above its rated capacity can overwhelm the separator, allowing more lubricant to escape into the system.
Maintaining the correct oil level in the compressor is crucial, as overfilling the reservoir forces excess oil into the air stream. A faulty or improperly set minimum pressure valve can also contribute by failing to maintain proper separator tank pressure. Another factor is oil degradation (or the use of incorrect lubricants), which can cause foaming and reduced separation efficiency, increasing oil carryover.
Worn seals, gaskets, or internal baffles in the separator tank may also allow oil to bypass the separator. If coalescing filters are clogged or faulty, they may fail to capture oil mist, allowing accumulation in downstream components. Frequent start-stop operation disrupts stable separation conditions, leading to slugging and higher oil contamination.
Regular inspections, oil changes, and proper maintenance of the compressor, separators, and filters are essential to minimizing oil accumulation and ensuring clean, efficient compressed air delivery.
Investigation of this customer revealed that the lubricant was coming from a lightly loaded variable speed drive compressor running below minimum speed, a point at which the internal separator is less efficient at removing oil. Adjustment of the operating parameters in this multi-compressor system allowed this compressor to turn off when not required, reducing the lubricant carryover problem.
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