BILGE EXERCISE: BILGE-QUESTIONS NAME:

1. Bilge pumps in a surveyed vessel must:

¨ be protected by strums, strainers or mud boxes
¨ be of a type, size and number as specified for the vessel
¨ have a separate power source when more than one pump is specified
¨ all of the above

2. Describe the main difference between strainers and mud boxes.
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3. What would happen to the bilge pumping system if a strainer was leaking around the lid?
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4. The most appropriate (single) valve to use in a bilge suction line would

¨ Gate valve
¨ Butterfly valve

¨ Screw-down non-return valve

5. A centrifugal pump is full of air due to maintenance on the strainers and suction pipes. What will happen when the pump motor is started?
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6. In a flexible impeller pump, water flows to the outlet because:

¨ centrifugal force flings water to the outside discharge
¨ the impeller lobes are bent by the offset plate, squeezing the water out
¨ the steel rotor distorts the rubber stator, forcing the fluid from the pump
¨ one-way flap-valves ensure the water only goes to the outlet

7. In a bilge system using strainers and centrifugal pumps, list the maintenance checks which should be regularly carried out.
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8. “Strums must be mounted in the bottom of the vessel to protect the end of a suction pipe, but strainers may be mounted higher where they are easier to reach!” How can pump suction draw bilge through the strainer without sucking air at the strainer?
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9. Sketch below the basic components of a surveyed 12 metre vessels bilge system.

BILGE ANSWERS

1. Bilge pumps in a surveyed vessel must:

¨ be protected by strums, strainers or mud-boxes
¨ be of a type, size and number as specified for the vessel
¨ have a separate power source when more than one pump is specified
þ all of the above

2. Describe the main difference between strainers and mud-boxes.
A mud box is similar to a strainer but has a dam at the base of the strainer plate.
Solids dropping off the strainer plate are retained in the dam, and prevented from falling back down the suction pipe into the bilge.

3. What would happen to the bilge pumping system if a strainer was leaking around the lid?
The bilge pump would suck air and may stop pumping
4. The most appropriate (single) valve to use in a bilge suction line would be:

¨ Gate valve
¨ Butterfly valve
þ Screw-down non-return valve
¨ Sleeve-packed cock

5. A centrifugal pump is full of air due to maintenance on the strainers and suction pipes. Explain what will happen when the pump motor is started.
The pump is full of air, and centrifugal pumps are not self-priming, so it will not pump This may damage pump seals if the pump is not shut-down and primed.

6. In a flexible impeller pump, water flows to the outlet because:
¨ centrifugal force flings water to the outside discharge
þ the impeller lobes are bent by the offset plate, squeezing the water out
¨ the steel rotor distorts the rubber stator, forcing the fluid
¨ one-way flap-valves ensure the water only goes to the outlet

7. In a bilge system using strainers and centrifugal pumps–list the maintenance which should be regularly carried out.
Strainers should be regularly cleaned and re-sealed, and pump seals and suction piping checked for leaks.

8. “Strums must be mounted in the bottom of the vessel to protect the end of a suction pipe, but strainers may be mounted higher where they are easier to reach!” How can pump suction draw bilge through the strainer without sucking air at the strainer?
Strainers are sealed, and effectively form part of the suction piping.

Ranger Hope © 2008, contains edited material courtesy of A.N.T.A publication’s.