🔍 Key Concepts

• Difference between positive displacement pumps and dynamic (centrifugal) pumps • How flow behaves in positive displacement pumps when discharge pressure changes • Typical examples of positive displacement pumps used on board (reciprocating, gear, rotary, screw, etc.)

💭 Think About

• 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? • Think about which of these pumps can safely run with a closed discharge valve without immediately damaging itself or its piping. • Consider which pump type is most commonly used as a ballast, fire, or cooling water pump, where large flow and variable head are needed.

✅ Before You Answer

• Be clear on the definition of a positive displacement pump: moves a nearly fixed volume per revolution or stroke, almost independent of discharge pressure. • Identify which choices are typically classified as positive displacement (reciprocating, gear, screw, rotary types). • 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.