Plant Operation, Maintenance and Monitoring
Plant operation, maintenance and monitoring - this domain tests routine operation: what you record, how you trend it, what maintenance keeps a plant efficient, and how you diagnose a fault from instrument readings rather than guesswork.
Rounds and records
Logs are evidence of control: suction and discharge pressures and temperatures, oil level and oil pressure, condenser approach, receiver and surge-drum level, motor amperage, water temperatures, and any abnormal noise or vibration. Trend the numbers instead of copying them - a slow drift in approach or a quiet fall in oil level is the earliest warning you will get.
Routine maintenance
- Oil: correct grade, changed on condition (acidity, moisture, viscosity), with oil return assured by correct gas velocity and traps.
- Purge non-condensables from the top of the condenser, where they collect.
- Clean condenser tubes and air-cooled coils; treat cooling water; check tower distribution.
- Test cutouts, calibrate sensors, check relief devices, and leak-check with an electronic detector (ammonia: sulphur stick or detector).
- Check belts, couplings, alignment, vibration and electrical terminations.
- Shutdown: pump down, isolate, tag, and protect water circuits from freezing.
Worked example
The liquid-line sight glass shows continuous bubbles. You measure 2 K subcooling at the condenser outlet, normal discharge pressure and a 4 K condenser approach. Normal approach rules out fouling, so low subcooling plus bubbles points to a flashing liquid line from a low charge or a low receiver level - find and repair the leak, then charge. Had subcooling instead read 20 K with high discharge pressure and a normal approach, non-condensables would be the suspect and purging is the fix.
Traps
Adding refrigerant on bubbles alone, without subcooling and approach. Purging liquid instead of vapour - wasteful and hazardous. Recording identical readings every day without looking at them. Ignoring a slow oil-level drop, which usually means a separator or oil-return problem. Treating a nuisance trip as a control problem rather than a symptom.