In hydraulic engineering of long pressure conduits, surge tanks are primarily installed to serve which operational purpose?

Introduction / Context:
Surge tanks are vertical chambers connected to long pressure pipelines that feed turbines or distribution systems. Their main role is to control pressure transients—commonly called water hammer—that arise when flow accelerates or decelerates rapidly due to valve or turbine gate movements. Understanding this purpose helps designers protect pipelines from overstress and maintain stable operations.

Given Data / Assumptions:

• We consider a long pressurized main connected to a reservoir and a demand (e.g., a turbine).
• Rapid flow changes can create large pressure waves.
• A surge tank provides a free surface connected to the main.

Concept / Approach:
When downstream demand suddenly decreases, momentum causes a pressure rise that travels as a surge. The surge tank provides an immediate volume buffer: water level in the tank rises, absorbing energy, and limiting peak pressure. Conversely, when demand suddenly increases, water level falls, supplying extra flow to curb negative pressures. This free-surface exchange mitigates the amplitude of transient waves, reducing risk of pipe rupture, joint failure, and equipment damage.

Step-by-Step Solution:
Identify the transient source: rapid valve/gate changes produce pressure waves. Recognize the surge tank's function: a nearby free surface allows inflow/outflow to absorb or supply momentum. Conclude: the device guards against water hammer by moderating pressure spikes and dips.

Verification / Alternative check:
Engineers also use air chambers, relief valves, and optimized control strategies. Yet, for long conduits feeding turbines, surge tanks are the classic, highly effective solution to restrain transients within allowable limits.

Why Other Options Are Wrong:

• Storage along the line: surge tanks are not intended as primary storage reservoirs.
• Increase velocity: their function is not to speed up flow.
• Overflow valves: a tank is not a valve; it does not automatically discharge to waste.
• Measuring discharge: surge tanks are not flow meters.

Common Pitfalls:

• Confusing surge tanks with service reservoirs or standpipes used for head stabilization in distribution networks.
• Assuming surge tanks eliminate all transients—they reduce, not fully remove, pressure waves.

Final Answer:
To guard the system against water-hammer (transient) pressures.