Auxiliary Machinery. Test 17 – 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 are subject to wear but mechanical seals are not
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
The sealing surface of a mechanical seal is parallel to the shaft, but sealing surface of a packed gland is perpendicular to the shaft
Packed stuffing box glands must be cooled by liquid, but mechanical seals do not require cooling

On a ship installation it is preferable on vertical pumps to have shaft sealing at the pump upper only. For what reason?

Adjustment of the seal if possible.
Containment of liquid in the pump over long idle periods.
Observance of conditions (i.e. leakage) if mechanically sealed.
All of the mentioned alternatives.

The purpose of the wear ring for the illustrated pump is to -

Support the end of the impeller.
Provide a replaceable wear surface for the shaft.
Provide a replaceable wear surface for the pump housing/impeller.
Absorb all impeller thrust.

Centrifugal pumps and displacement pumps differ in several characteristics. Which of the following statements regarding a centrifugal pump is correct?

A centrifugal pump is designed to take suction from 30 - 35 meters heigth (suction height).
The inlet is in the outer diameter of the impeller and the pressure discharge is in the center of the impeller.
A centrifugal pump is always fitted in a vertical possition.
It is important that the rotation direction is correct to avoid dry running.

The electric motor on one of your centrifugal pumps has for a period of time gradually been running at lower and lower Amp-load. The pump is still supplying water, but the pressure is reduced. Which of the below alternatives is probably the reason?

The pump has been more effective because the suction strainer has been removed.
Inner diameter of impeller is bigger due to cavitations, or outer diameter reduced by erosion.
The pump is running at lower speed due to short circuit in the electric motor.
The pump has suction from many places at the same time.

In a low pressure auxiliary boiler, what would You consider to be the normal operating range of phenolphthalein alkalinity?

500 - 1000 PPM CaCO3.
300 - 600 PPM CaCO3.
0 - 100 PPM CaCO3.
100 - 300 PPM CaCO3.

In a low pressure auxiliary boiler, if after testing the water You found the P. alkalinity to be 450 PPM CaCo3, what action would You take?

Do nothing.
Decrease dosage.
Increase dosage.
Blow down boiler and reduce dosage.

You have emptied the bilge well in the engine room using the bilge pump. After stopping, why is it important that all valves are closed ?

For safety reasons, otherwise seawater could enter the engine room.
To avoid corrosion inside the pump.
To keep the pumphouse empty for fluid to ensure an easier start of the pump.
To avoid the pumphouse to be emptied for fluid.

What is the main purpose of routine testing of cooling water?

To detect presence of contaminants in the water
To detect dissolved oxygen in the water
To measure the pH - value of the water
To ensure that the proper residuals of treatment chemicals, as specified, are maintained at all times

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