Question

Pressure inside the casing of an impulse turbine is

• A. Negative pressure
• B. Positive pressure
• C. Atmospheric pressure
• D. Atmospheric pressure

Hint:

Turbines: \[ \boxed{ \begin{aligned} \text{Impulse Turbine} &\rightarrow \text{Atmospheric pressure at runner}\\ \text{Reaction Turbine} &\rightarrow \text{Pressure changes across runner} \end{aligned} } \]

Answer 1

The Correct Option is C

Step 1: Recall how an impulse turbine works.
In an impulse turbine such as a Pelton wheel, the nozzle converts the entire available head into a high velocity jet before it strikes the buckets, so there is no pressure energy left to convert inside the casing.
Step 2: Think about what the casing is doing.
The casing here just shields the runner and directs the used water to the tailrace, it is not sealed to hold pressure the way a reaction turbine casing is.
Step 3: State the casing condition.
Since the jet and the runner both operate exposed to air, the casing remains at atmospheric pressure.
\[ \boxed{\text{Atmospheric pressure}} \]