š Key Concepts
ā¢ Difference between positive displacement pumps and dynamic (centrifugal) pumps
ā¢ How flow behaves in positive displacement pumps when discharge pressure changes
ā¢ Typical examples of positive displacement pumps used on board (reciprocating, gear, rotary, screw, etc.)
š Think About
ā¢ First, recall what makes a pump "positive displacement" in terms of trapping and moving a fixed volume of liquid each cycle. Which type in the list does NOT work that way?
ā¢ Think about which of these pumps can safely run with a closed discharge valve without immediately damaging itself or its piping.
ā¢ Consider which pump type is most commonly used as a ballast, fire, or cooling water pump, where large flow and variable head are needed.
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Before You Answer
ā¢ Be clear on the definition of a positive displacement pump: moves a nearly fixed volume per revolution or stroke, almost independent of discharge pressure.
ā¢ Identify which choices are typically classified as positive displacement (reciprocating, gear, screw, rotary types).
ā¢ Check which one is normally classified as a centrifugal or dynamic pump, where flow changes significantly with head and which is NOT considered positive displacement.