First Assistant Engineer · 1AE01 · Engine · Potable Water Systems · CURRENT-Q511-Q0019
Hydropneumatic Tanks: Recognizing Waterlogging
Connect loss of the compressed-air cushion to short, frequent potable-water pump cycles.
What are the operating characteristics of a “waterlogged” potable water system hydro-pneumatic header tank that needs to be recharged with compressed air?
- A. Failure of the potable water pump to stop with zero demand on the system.
- B. Failure of the potable water pump to start with demand on the system.
- C. Very short and frequent running and idle periods for the potable water pump.
- D. Extremely long running and idle periods for the potable water pump.
Correct answer: C. Very short and frequent running and idle periods for the potable water pump.
Why this answer is correct
A waterlogged hydro-pneumatic tank causes very short, frequent pump runs and stops because the air cushion and usable drawdown volume are lost.
Governing principle
Compressed air stores pressure energy; water is nearly incompressible and cannot provide the same buffer.
Reasoning
- The tank's air cushion compresses as the pump raises pressure.
- When that cushion is lost, very little water can be withdrawn between cut-out and cut-in pressures.
- The pump therefore starts and stops rapidly and frequently.
Why the other choices do not fit
A. A pump that never stops suggests another control, leakage or capacity problem, not the characteristic waterlogged-tank pattern.
B. Failure to start points to controls, power or pump trouble.
D. Waterlogging reduces, rather than lengthens, the running and idle cycle.
Related lesson
Potable-Water Pressure Systems
Flashcard preview
What is the purpose of the air cushion in a hydropneumatic potable-water tank?
A hydropneumatic pressure tank uses a compressed-air cushion to maintain pressure and reduce pump cycling. If the tank becomes waterlogged, the pump tends to start and stop in very short, frequent cycles.
Sources
- Maine Department of Health and Human Services · Maintaining Pipes and Storage Tanks · Waterlogged hydropneumatic tank signs, including very short pump cycling
- USCG National Maritime Center · Q511 General Subjects I · Question 19 and official answer key
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