Classification of positive displacement pumps and rotodynamic pumps.

  • Water drain and oil from various places of the engine room are collected in the bilge. They are pumped through an oily bilge separator to make sure that oil content is removed and only water is pumped out to sea, the removed oil in the oily bilge separator is transferred to the bilge collectors. normally a positive displacement pump is used for this purpose. 
  • when there is no cargo on board the ship, the weight of the ship becomes lighter and may bring a problem to the ship's stability. so in order to maintain the stability of the ship the ballast tanks are filled with water by ballast water pumps. generally, these pumps are centrifugal pumps or rotodynamic pumps.

Classification of Pumps

Based on working principle the pumps are classified into:

positive displacement pumps vs Rotodynamic pumps
positive displacement pumps Rotodynamic pumps
Displacement of liquid is achieved by mechanical difference of the pump casing. Velocity of the liguid is increased by spining the liquid at high speed with the help of a rotating impeller.
Increase in energy takes place periodically. continuous increase in energy.
It does not require priming. Priming is required.
Increase in pressure of a liquid is based on the displacement of liquid. Pressure of liquid increases with increase of liquid velocity by volute casing.
Capable of transferring low volume of liquid at high pressure. Capable of transferring high volume of liquid at low pressure.

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