Dräger Primus: moisture and oil in the gas path, valves destroyed
What happened
Reported case: water and compressor oil entered the machine's gas supply path. During the self-test the engineers described a 'detonation' of oil vapour at the heated flow sensor — the inspiratory and expiratory valves and the breathing circuit were destroyed by the pressure wave.
What was checked
- The engineers stripped the rotameter and dried its parts.
- They purged the tubing with oxygen in the direction of the normal air flow.
- The filter in the air inlet connector was dried out.
- Dry gas delivery through the rotameter was confirmed in manual mode before the unit was considered usable.
Cause
In this case the central air supply came from an old oil-lubricated compressor without a dryer. The water-and-oil mixture was carried into the machine, and the heated element of the flow sensor ignited the oil vapours — with oxygen present, this ended as reported.
What was done
The engineers disassembled and dried the rotameter, tubing and inlet filter, purged the gas lines with oxygen, and verified dry gas flow. As reported, the machine was then left purging with air through the open rotameter at about 5 L/min for several hours before returning to use. The fault was resolved in this case.
Safety
Never connect an anaesthesia machine to an air supply from an oil-lubricated compressor without a dryer and proper filtration — oil mist with pressurised oxygen is a serious fire and explosion hazard, and the machine must pass the full manufacturer's pre-use check before it goes anywhere near a patient.
Lesson: The quality of the medical gas supply is part of the machine: any new or improvised air source must be dry and oil-free, otherwise contamination can end in destroyed valves — or worse.
Covered in the course: Anaesthesia Machine Service — Level 2: Fault-Finding →
Written from an anonymised case shared by service engineers. It is not a manufacturer instruction and grants no authorisation. Independent note; names are trademarks of their owners.