USCG Exam PracticeHydraulics and pneumatics
A reciprocating air compressor is running and the discharge valve to the air receiver is inadvertently closed while the compressor continues to operate. Based on NAVEDTRA 14075 §7-1 and NAVEDTRA 14104 §10-3, what is the primary reason this condition is hazardous, and what design feature is required to address it?
- A. The compressor will overheat due to loss of cooling airflow; a thermostat-controlled shutdown is required.
- ✓ As a positive-displacement machine, the compressor must never run against a closed discharge; each stage must therefore be protected by its own relief valve.Correct
- C. Moisture will accumulate in the cylinder because the aftercooler cannot drain with the discharge valve closed; a drain trap on each stage is required.
- D. Oil carryover will increase rapidly because the separator cannot function without airflow; an oil-mist detector is required to shut down the compressor.
Why B is correct
Both NAVEDTRA 14075 §7-1 and NAVEDTRA 14104 §10-3 state that positive-displacement compressors must never run against a closed discharge, and that each stage must therefore be protected by its own relief valve. Running against a closed discharge will cause pressure to build without limit, creating a catastrophic overpressure hazard.