Pump selection preliminaries: A typical overall efficiency to assume for a complete pumping set (pump + drive + minor losses) in preliminary design is

Introduction / Context:
In early-stage estimates, designers often use a representative overall efficiency to convert water horsepower to brake horsepower. This includes pump hydraulic efficiency, mechanical losses, and drive losses (e.g., motor or engine efficiency).

Given Data / Assumptions:

• No manufacturer curves available yet.
• Conventional clean-water pumping duties.
• Motor-driven set, moderate head and flow.

Concept / Approach:

Overall efficiency η_overall = η_pump * η_mech * η_motor. For preliminary purposes, many teaching references suggest 60% as a reasonable assumption, pending refinement once specific equipment is selected.

Step-by-Step Solution:

Verification / Alternative check:

Final designs replace the assumed value with catalog data. High-efficiency installations may exceed this; others (e.g., small pumps, poor suction conditions) may be lower.

Why Other Options Are Wrong:

• 50–55%: conservative but sometimes too low for modern sets.
• 65–70%: achievable in optimized selections but less safe as a default assumption without data.

Common Pitfalls:

• Treating the preliminary assumption as fixed for procurement.
• Ignoring part-load efficiency variation.

Final Answer:

60%.