Short Answer:

Surge tanks help in mitigating water hammer effects by absorbing sudden pressure changes in long pipelines. When the flow of water is quickly stopped or changed, surge tanks provide a space for excess water to rise and fall, reducing the impact of pressure waves.

They act as a buffer between the source and the rest of the pipeline, preventing high-pressure shocks from damaging the system. By controlling these pressure surges, surge tanks protect pipelines, valves, and pumps, making the hydraulic system safer and more stable.

Detailed Explanation

Surge tanks in mitigating water hammer effects

Water hammer is a sudden rise in pressure caused by a rapid change in water flow, such as when a valve closes quickly or a pump stops suddenly. This pressure surge creates a shock wave that travels through the pipeline, which can lead to pipe bursts, joint failure, or equipment damage. Surge tanks are special structures installed in water conveyance systems—especially in long pipelines and hydropower plants—to control these dangerous pressure variations.

A surge tank is a vertical chamber or tank connected to the pipeline. It is partially filled with water and has an open or closed top to allow water movement. It provides a space where excess water can go when pressure suddenly increases, and from which water can be drawn when pressure drops. This action balances the system and prevents severe fluctuations.

How Surge Tanks Work:

Absorbing Excess Water During Pressure Rise:
When a sudden closure of a valve or pump shutdown occurs, water that was in motion suddenly has no place to go. Instead of slamming into a closed valve, the water enters the surge tank and rises. This reduces the pressure in the pipeline and avoids the creation of a strong shock wave.
Supplying Water During Pressure Drop:
If there’s a sudden increase in demand or a pressure drop, water from the surge tank flows back into the pipeline, maintaining a continuous flow and preventing negative pressures (which can cause pipe collapse or air entry).
Dampening Pressure Waves:
Surge tanks act like a cushion that absorbs and releases energy as needed. They slow down and reduce the strength of pressure waves, preventing them from traveling back and forth in the pipeline.

Types of Surge Tanks:

Simple Surge Tank: An open tank directly connected to the pipeline.
Closed Surge Tank: A sealed tank with air cushioning.
Surge Chamber with Restriction: A tank with an orifice or throttling device to control flow in and out.
Differential Surge Tank: More advanced, with internal risers to regulate flow based on pressure changes.

Advantages in Civil Engineering Systems:

Protects pipelines in hydroelectric projects, long gravity pipelines, and high-head water supply lines.
Reduces mechanical stress on valves, joints, and pumps.
Improves system stability, especially in systems with rapid flow changes.
Lowers maintenance and repair costs by preventing structural damage.
Provides a quick response to pressure changes without using electrical or mechanical controls.

Design Considerations:

Civil engineers must calculate the correct height, diameter, and location of the surge tank based on flow rate, pipe length, pressure range, and elevation. Poor design or incorrect sizing may lead to ineffective pressure control or system imbalance.

Conclusion:

Surge tanks play a crucial role in reducing the damaging effects of water hammer by absorbing sudden pressure rises and supplying water during drops. They act as a balancing device in pipelines, especially in long-distance or high-pressure systems. By controlling pressure surges, surge tanks improve the safety, reliability, and performance of hydraulic systems in civil engineering applications.