Pumps and appurtenances in water-supply engineering: Which one of the following statements is INCORRECT about common pump types and their principles of operation?

Introduction / Context:
Pumps used in water-supply systems include air-lift pumps, jet (ejector) pumps, hydraulic rams, centrifugal pumps, and rotary positive-displacement pumps. Each type has a distinct principle, typical application, and installation constraint. This question checks recognition of correct operational principles and a common distractor about “cams” in rotary pumps.

Given Data / Assumptions:

• Deep and small-diameter wells often require special pump arrangements.
• Hydraulic ram devices use pressure surges (water hammer) to lift water.
• Rotary pumps generally use gears, lobes, vanes, or screws rather than “cams”.

Concept / Approach:
Identify the statement that mischaracterizes a pump’s working mechanism. Air-lift and jet pumps move water by entrained air or jet-induced suction respectively; hydraulic rams exploit water hammer. Rotary pumps are positive-displacement units employing gears/lobes/vanes/screws, not opposing “cams”.

Step-by-Step Solution:

Verification / Alternative check:
Manufacturer catalogs and standard texts depict internal gear, lobe, vane, and screw pumps; none rely on counter-rotating “cams” as the primary displacement element in waterworks service.

Why Other Options Are Wrong:

• Option a: Describes air-lift principle accurately.
• Option b: Correctly notes small-well suitability of jet pumps.
• Option c: Properly cites water-hammer basis for hydraulic rams.
• Option e: Not applicable because one statement (d) is wrong.

Common Pitfalls:
Confusing rotary positive-displacement internals with cam-and-follower mechanisms; mixing centrifugal and rotary PD concepts; assuming all deep-well pumping uses submersible centrifugal pumps.

Final Answer:
Rotary pumps use cams that rotate in opposite directions to move water.