Reciprocating pump — classification by displacement A reciprocating pump is also called a ________ displacement pump. Choose the correct term used in fluid machinery.
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Apositive
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Bnegative
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Cvariable-inertia
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Dnon-displacement
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Ecentrifugal
Answer
Correct Answer: positive
Explanation
Introduction:Pumps are broadly divided into positive displacement (PD) and rotodynamic categories. Recognizing which class a reciprocating pump belongs to is essential for understanding its flow characteristics, control methods, and protections.
Given Data / Assumptions:
- Piston/ plunger mechanism with suction and delivery valves.
- Finite swept volume per stroke; relatively low speed.
Concept / Approach:Positive displacement machines transfer a nearly fixed volume of fluid each cycle irrespective of discharge pressure (within mechanical limits). Reciprocating pumps trap fluid in a chamber and displace it by piston motion, making them quintessential PD pumps. Consequently they require relief valves to prevent overpressure and often benefit from air vessels to smooth pulsating flow.Step-by-Step Solution:
Identify operating principle: trapping and forcing fixed volumesRelate to definition: flow nearly proportional to speed, not headConclude: “positive displacement” is the correct classificationVerification / Alternative check:Manufacturer curves for PD pumps show near-vertical head–flow characteristics: flow rate changes little with discharge pressure compared to centrifugal pumps.
Why Other Options Are Wrong:
- Negative/non-displacement/centrifugal: do not describe reciprocating mechanisms.
- Variable-inertia: not a standard category.
Common Pitfalls:Operating PD pumps with closed discharge without relief valves; confusing their control logic with that of centrifugal pumps.
Final Answer:
positive