Centrifugal pumps (radial flow) – casing types and efficiency:\r Which statements correctly describe volute (involute) and turbine/diffuser type casings used with radial flow centrifugal pumps, and their typical efficiency trend?

Introduction / Context:
Centrifugal pumps convert mechanical shaft power into hydraulic energy by imparting velocity to water in the impeller and then converting that velocity head to pressure head in the casing. This question checks understanding of the two common casing philosophies for radial flow pumps and their impact on efficiency and operation.

Given Data / Assumptions:

• Pump type: radial flow centrifugal pump.
• Casing alternatives: volute (involute spiral) and turbine or diffuser type with guide vanes.
• Comparison concerns construction and typical efficiency.

Concept / Approach:
The volute casing is a spiral passage of increasing area that slows the high velocity discharge from the impeller and partially converts kinetic energy into pressure. The diffuser or turbine casing uses a ring of stationary guide vanes around the impeller to decelerate flow more uniformly before collecting it, which tends to give better energy recovery and a higher hydraulic efficiency for a given duty, especially near design flow.

Step-by-Step Solution:
Identify features: volute equals expanding spiral passage; diffuser equals stationary guide vanes plus collection.Energy recovery: both reduce velocity to raise static pressure; diffuser does so more uniformly.Efficiency trend: diffuser casings typically achieve higher efficiency under design conditions than simple volutes.Therefore all listed statements are consistent with standard pump theory and practice.

Verification / Alternative check:
Manufacturer curves frequently show diffuser pumps with slightly higher peak efficiencies. Volute pumps remain popular due to simplicity, robustness, and wider tolerance to off-design operation, but do not negate the general efficiency edge of diffuser designs.

Why Other Options Are Wrong:

• Any single statement alone is incomplete. The inclusive choice encompasses construction, flow guidance, and efficiency.

Common Pitfalls:

• Confusing axial flow casings with radial flow casings.
• Assuming volutes are always superior due to simplicity; efficiency trends favor diffusers at design conditions.

Final Answer:
All of the above