Pumps

Question 1

How to prime a centrifugal pump

Answer 1

Ensure discharge v/v is closed
Use an air eductor to remove air
Start p/p and open discharge v/v slowly

Question 2

How does a centrifugal pump work?

Answer 2

It uses Bernoulli’s principle to convert kinetic energy to pressure energy (velocity to pressure) by using centrifugal force to force liquid outwards. As it travels outwards the area is expanding and slowing the velocity while increasing pressure as a result.
The outwards movement of the liquid creates a low pressure area at the eye where more liquid will be attracted due to the pressure in the line/tank being higher.

Question 3

How does a gear pump work?

Answer 3

-Suction (inlet): as the gears rotate the teeth become unmeshed where they create an expanding volume that the water is drawn in to
-Transport: the water is then sent around the casing with the teeth
-Discharge (outlet): as the teeth mesh the volume is then reduced and the water is pushed out

Question 4

What is a key feature of axial pumps?

Answer 4

Axial pumps are reversible so they can be used for heeling systems

Question 5

You are shown a pistons suction and discharge gauges, what problems may there be with the pump if there is no discharge or suction?

Answer 5

-A hole may be present in the pipe
-The strainer gasket is damaged
-The bilge well for a different compressor has been opened
-The suction valve is not reseating (fouled)

Question 6

You are shown a pistons suction and discharge gauges, what problems may there be with the pump if there is High suction and no discharge?

Answer 6

-The strum box is blocked
-Strainer is blocked

Question 7

A pumps gauges are showing high discharge and high suction, what may be wrong?

Answer 7

The discharge valve is closed

Question 8

Explain what a positive displacement pump does and give some examples of positive displacement pumps

Answer 8

-It generates a fixed pressure by providing volume with every rotation.
-they are self priming
-Gear, screw and vane

Question 9

Difference between an ejector and eductor

Answer 9

Ejector is driven by air and an eductor is driven by water