Pelton Wheel — Double Overhung Configuration In Pelton turbine layouts, what does the term “double overhung” specifically indicate about the number of runners on the shaft?

Introduction:
Pelton wheels are impulse turbines used for high heads and relatively low discharges. Plant layouts are often described as single overhung or double overhung depending on how runners are mounted on the shaft. The question tests recognition of this practical configuration terminology.

Given Data / Assumptions:

• Impulse turbine (Pelton) with one shaft supported by bearings.
• “Overhung” means mounted outside the bearing span.
• “Double overhung” implies symmetric mounting at both shaft ends.

Concept / Approach:
In a single overhung Pelton arrangement, one runner is mounted at one end of the shaft. In a double overhung arrangement, there are two runners—one mounted at each end—so that multiple jets (often two per runner in compact plants) can be used while keeping bearing loads balanced and overall width manageable.

Step-by-Step Solution:
Interpret the term: “double” refers to two overhung mountings.Each overhung position carries a runner.Therefore the configuration has two runners on the same shaft.

Verification / Alternative check:
Installation drawings and manufacturer catalogs show double overhung Pelton sets with a runner at each shaft end.

Why Other Options Are Wrong:
two jets: jet count is independent of the “overhung” term.four jets: possible in some plants, but the term denotes runners, not jet number.four runners: uncommon and not implied by the nomenclature.

Common Pitfalls:
Confusing number of jets with number of runners; jets per runner vary by design.

Final Answer:
two runners