Hydraulic Transients – Purpose of a Surge Tank in Pipe Systems In high-head water conveyance (penstocks), a surge tank is provided to control pressure variations due to rapid flow changes, mitigate water-hammer effects, and help regulate the flow to turbines by supplying or absorbing the required retarding head.

Introduction:
Surge tanks are tall standpipes or reservoirs connected to long pipelines between a reservoir and a turbine. They buffer rapid changes in discharge and protect the system from damaging pressure surges known as water hammer, while also improving turbine control.

Given Data / Assumptions:

• Long conduit conveying water to hydraulic turbines.
• Rapid load changes at the turbine can cause sudden velocity changes.
• Tank is properly located near the powerhouse or along the penstock.

Concept / Approach:

When turbine demand drops suddenly, decelerating water can cause large positive pressure spikes. A surge tank provides a free surface where water level can rise, absorbing inertia and reducing the transient pressure. Conversely, when demand increases, water level falls in the tank to supply additional flow, reducing negative pressure spikes and aiding regulation.

Step-by-Step Solution:

Verification / Alternative check:

Water-hammer analysis using elastic wave speed and continuity shows reduced peak pressures when a free surface reservoir is introduced near the turbine.

Why Other Options Are Wrong:

Any single choice understates function; the device is specifically installed to address all listed roles in concert.

Common Pitfalls:

Assuming a surge tank eliminates water hammer completely regardless of valve speed; in reality, it mitigates but does not remove all transients if operations are extreme.

Final Answer:

all of the above