Impulse vs reaction turbines — identify the correct statement Choose the statement that correctly describes pressure/energy conditions across the runner for impulse and reaction turbines.

Introduction:
Understanding where pressure changes occur differentiates impulse and reaction machines. Correctly identifying these conditions is vital for selecting casings, draft tubes, and governing systems.

Given Data / Assumptions:

• Impulse (e.g., Pelton) uses nozzles to convert pressure head fully to jet velocity before the runner.
• Reaction (e.g., Francis/Kaplan) allows pressure changes across runner passages.

Concept / Approach:
In impulse turbines, jets strike buckets at atmospheric pressure; the runner primarily redirects momentum with negligible pressure change. In reaction turbines, both pressure and velocity change across the runner blades, producing lift-like forces while the casing and draft tube contain sub-atmospheric regions.

Step-by-Step Solution:

Verification / Alternative check:
Pelton installations show free jets and open buckets exposed to atmosphere; reaction turbines require sealed casings and draft tubes due to pressure variations.

Why Other Options Are Wrong:

• Pressure energy at impingement (impulse): nozzle already converted it to velocity head.
• “Kinetic only” for reaction: reaction also involves pressure changes.
• Pressure increases over reaction vanes: it typically decreases as energy is extracted.
• Both constant: false for reaction machines.

Common Pitfalls:
Confusing nozzle exit conditions with runner passage conditions; assuming enclosed casings imply constant pressure.

Final Answer: