Pumping Systems, Operations. Test 10 – Online Maritime Tests

What is the main difference between a stuffing box gland and a mechanical seal on a centrifugal pump?

Packed stuffing box glands must be cooled by liquid, but mechanical seals do not require cooling
Packed stuffing box glands are subject to wear but mechanical seals are not
The sealing surface of a mechanical seal is parallel to the shaft, but sealing surface of a packed gland is perpendicular to the shaft
If packing fails the pump can be kept running by tightening the glands, but if a mechanical seal fails it must be renewed to stop the leakage

In a centrifugal pump, low pressure regions may occur in the flow at points where high local velocities exist. If vapourisation occurs due to these low pressure areas then bubbles occur. Such formation and collapse of bubbles is very rapid, and can generate very high pressure hammer blows which results in pitting, noise, vibration, and a fall off in the pump efficiency. Is this known as:

Cavitation.
Priming.
Fouling.
Viscosity.

What is the correct parts description list of this pressurised filter ?

1 = Filter cover, 2 = Ribbed filter cartridge, 3 = Filter body.
1 = Filter top, 2 = Filter cloth, 3 = Housing body.
1 = Top plate, 2 = Mesh cloth, 3 = Housing.
1 = Top cover, 2 = Element, 3 = Cast body.

This in terms of overall pump performance, what is the most important negative effect if an impeller wear ring (No 6) is worn excessively ?

The pump starts vibrating, bearing damage will occur.
The pump will absorb excessive power, motor overload.
The housing will be attacked by cavitation.
The pumping efficiency deteriorates, less output.

If when in port there is an urgent requirement to pump bilge water from the vessel, what would you do?

Pump bilges in a dirty oil tank or sludge tank and note in logbook.
Pump the bilges over the sides via the oily water separator.
Lower the bilges only during night time.
Pump the bilges only to a shore or barge reception facility.

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