For preliminary hydraulic design, what is a reasonable assumed efficiency for a typical pump when exact performance curves are unavailable?

Introduction:
Pump efficiency (η) = water horsepower / shaft horsepower. In early‐stage design and quick checks, engineers adopt representative values to size motors and estimate energy use before selecting a specific pump curve.

Given Data / Assumptions:

• Pump type is not specified; assume a conventional centrifugal pump.
• Field installation and off-BEP operation often reduce ideal efficiencies.

Concept / Approach:
Typical field efficiencies for medium-size centrifugal pumps cluster around 60–70%. A mid-range assumption balances conservatism with realism for screening studies and preliminary power estimates.

Step-by-Step Solution:
Select a representative mid-range η.0.65 is widely used as a planning-level default.Refine later with manufacturer's BEP curves and system curve intersection.

Verification / Alternative check:
Design handbooks and codes of practice list similar ranges; detailed selections may exceed 70% under ideal conditions but should not be assumed globally.

Why Other Options Are Wrong:

• 0.55: Too conservative for a general assumption.
• 0.60: Acceptable but typically not the default mid-range pick.
• 0.70: Feasible for selected units near BEP; optimistic for general assumptions.

Common Pitfalls:

• Using best-case lab efficiency in field energy estimates.

Final Answer:
0.65.