Sounding & Level Measurement — Most Asked Questions
7 questions asked about sounding & level measurement across the General and Fn 6 and Fn 3 papers, heaviest first.
Learn the system first
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1 How will you check boiler low low level alarm?
Also asked: “How to test boiler low level alarm”
Answer
Prove the low and low-low alarms for real by dropping the water level in the chamber — never by just pressing the test button.
- Test on every watch or daily: drain/blow down the float chamber so the floats actually fall with the level.
- Low-water alarm must sound first; at low-low the burner must cut out and lock out — confirm both, not just the bell.
- On a water-tube boiler a lost level turns dangerous in minutes from high evaporation rate and small reserve, so class demands the protection.
- After the test blow through the gauge glass, refill the chamber and reset — log time, level and burner response.
Surveyor follow-up: alarm sounds on test but the burner keeps firing — what has failed?
Full theory: Boiler Safety Devices and Emergency Response -
2 Piston ring calibration?
Answer
Calibrate rings by groove and gap: feeler top and bottom against the data-plate figure with butt gap proved in the liner.
- Read vertical clearance top plus bottom with feelers; the total must sit inside the plate figure.
- Sudden wear jumps mean water through the cooler, dead cylinder oil or abrasive fuel and air.
- Proving the ring free in its groove matters more than polishing it — stuck rings pump blow-past.
- Butt gap proved square in the unworn liner band per maker figure before fitting.
Surveyor follow-up: one unit high exhaust with low compression — rings, valves or timing, and what do you measure first?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
3 Calibration of o2 analyzer
Also asked: “Oxygen analyser calibration”
Answer
Calibrate the O₂ analyser dead-steady: nitrogen for zero, dry air for span, two minutes to settle each time.
- Zero on nitrogen at the 0–1% range with flow set, trimming the zero knob to a true zero reading.
- Span on dry air through silica gel, waiting two minutes to equilibrium, trimming span to 21% O₂.
- A cold cell reads nothing — warm it first; 21% with sample gas flowing means blocked pipe, broken cell or meter fault.
- Log zero and span drift each watch; recalibrate after filter, pipe or cell work before trusting the bridge reading.
Surveyor follow-up: analyser stuck on 21% with flue gas applied — calibrate, warm up or open the sample line first?
Full theory: Instruments & Safety Systems -
4 liner calibration in details
Also asked: “How liner calibration is done?”, “How to take liner calibration”
Answer
Liner calibration maps wear against hours: gauge each cylinder fore-aft and athwart at fixed levels, record on the template.
- Gauge with an inside micrometer at top, middle and bottom of stroke, fore-aft and port-starboard each.
- Record cylinder number, date fitted, total hours and hours since last gauging on the measurement template.
- Compare against original bore for wear rate, ovality and taper — scavenge-port and top-ring zones wear fastest.
- Rising rate with steady hours condemns oil feed, fuel sulphur match or air filtration before the liner does.
Surveyor follow-up: one cylinder oval with the rest round and hours equal — gauging error, lubrication or alignment?
Full theory: Cylinder Liner Wear, Calibration & Cold Corrosion -
5 Air pipe and sounding pipe regulation
Answer
Air pipes breathe the tank and sounding pipes measure it: both are placed by rule, at the right height, and closed against fire.
- Air pipes go opposite the filling pipe and at the highest point, led above the bulkhead deck or to open deck for oil tanks.
- The height is not less than about 760 mm on the freeboard deck and 450 mm on the superstructure deck.
- Sounding pipes are as straight as possible, bore not less than 32 mm, and 65 mm through a refrigerated compartment.
- Striking plates of adequate size and thickness go under open-ended sounding pipes, with the cover self-closing where it must be.
Surveyor follow-up: sounding pipe with no striking plate and a 20 mm bore in a reefer compartment — which rule is broken first?
Full theory: Ship Pipelines — Seawater, Bilge, Ballast & Fuel Systems -
6 How to calibrate gas detector ( by span gas
Answer
A detector is proved on two gases: zero on nitrogen or fresh air, span on a known gas, and a bump test between.
- Zero on nitrogen or clean air with the flow set, adjusting the zero knob to a true zero reading.
- Span on a certified cylinder of known concentration, allowing the reading to settle, and trimming the span control to match.
- Between calibrations, a bump test with known gas proves it is still reading — the single check that catches a failed sensor.
- Record the cylinder concentration and date, because a span check against an unknown gas proves nothing.
Surveyor follow-up: detector passing the bump test but failing span — the sensor, the cylinder or the sample line?
Full theory: Instruments & Safety Systems -
7 Procedure fo calibrating gas detector
Answer
Calibrate in order: clean, flow, zero, span, bump — and never with the cell cold or the sample line blocked.
- The analyser will read falsely if the meter circuit resistance is high, the cell defective or broken, or the pipe blocked.
- Zero first on nitrogen or fresh air, then span on the certified gas, reading the certificate value rather than a nominal one.
- The cell will not operate when cold — allow it to reach working temperature before trusting any reading.
- Finish with a bump test, and log the gases, concentrations and dates against the instrument register.
Surveyor follow-up: detector reading 21% on flue gas with the sample line proved clear — is it the cell, the meter circuit or a short?
Full theory: Instruments & Safety Systems
Source: 123 written papers and surveyor oral banks, 24,613 entries, merged into 17,210 topics. Ticks are stored on this device only.