Water Hammer: What It Is, Why It Occurs, and How to Protect a Pressure System

Under normal conditions, a pressurized system operates at specific levels of pressure, velocity, and flow rate. When any of these variables changes suddenly, the fluid’s energy does not disappear immediately: it transforms into a pressure wave that travels through the system.

This wave can increase or decrease the pressure at different points in the system and be reflected by valves, changes in pipe diameter, tanks, pumps, and other components of the system.

The phenomenon can result from scheduled operational changes or unforeseen events. Among the most common causes are:

• Rapid closing or opening of valves

When a valve closes rapidly, the moving fluid is decelerated in a very short period of time. This can cause a sudden increase in pressure upstream and a decrease in pressure downstream.

The valve’s operating speed, its location, and the characteristics of the piping directly influence the system’s response.

• Sudden pump shutdown

An electrical failure or an emergency shutdown can cause an abrupt decrease in the pumped flow rate. The water column continues to move by inertia, which can lead to pressure drops, flow reversal, and subsequent overpressures.

• Pump startup

Starting one or more pumps also alters the system’s flow rate and pressure. Starting too quickly can cause hydraulic transients, especially in large systems or those with high fluid volumes.

• Power Outages

A power outage can simultaneously shut down the pumps and other control components. Depending on the hydraulic configuration, this event can trigger a complex sequence of pressure drops, flow reversal, and check valve closure.

• Abrupt Closure of Check Valves

When flow reversal occurs, a check valve may close abruptly. This closure can generate significant overpressure and impose additional stresses on the piping and its supports.

• Operational changes to the system

The addition or removal of pumps, speed variations, changes in tank levels, and flow rate modifications can also produce transient conditions that must be considered during design and operation.

Water hammer is not limited to a pressure surge. Depending on the system configuration, it can also cause extremely low pressures and other hydraulic phenomena.

Among its main effects are:

• High Overpressures

A pressure wave can exceed the design pressure of pipes, valves, joints, and fittings. Repeated occurrences of these events can also accelerate component fatigue, even when no immediate failure occurs.

• Underpressure

A sudden drop in pressure can create near-vacuum conditions, cause deformation in vulnerable pipes, or allow air to enter through points not designed for that purpose.

• Cavitation

When pressure drops below the vapor pressure of the liquid, cavities or vapor bubbles may form. As pressure recovers, these cavities collapse and can cause vibrations, noise, and localized damage.

Cavitation can occur locally or be distributed over a longer section of the pipeline.

• Vibrations and Structural Stresses

Pressure variations generate dynamic forces that can be transmitted to pipes, supports, anchors, valves, and equipment. This can cause movement, vibrations, loosening of joints, or structural damage.

• Operational Failures

Transients can also cause unscheduled activation of protective devices, equipment shutdowns, loss of operational continuity, and increased maintenance requirements.

There are various measures to reduce the effects of hydraulic transients. The most appropriate alternative depends on the results of the analysis and the specific conditions of the installation.

Measures that can be evaluated include:

• • Modifying valve opening and closing times.
• • Controlling pump start-up and shutdown ramps.
• • Proper selection of check valves.
• • Installation of air or relief valves.
• • Use of control and automation equipment.
• • Installation of hydropneumatic tanks or damping systems.
• • Combination of different protective devices.

Hydropneumatic tanks are one of the alternatives used to protect discharge lines against sudden pressure fluctuations.

These devices combine a volume of liquid with a volume of compressible gas. When a pressure change occurs, the gas can compress or expand, allowing the reservoir to temporarily receive or deliver fluid to the system.

In this way, the tank helps reduce the magnitude of overpressures and underpressures, dampening the hydraulic response to transient events.

Depending on the project requirements, different configurations may be considered, including:

• • Hydropneumatic tanks with a diaphragm.
• • Tanks with a compressed air system.
• • Nitrogen-pressurized tanks.
• • Vertical or horizontal configurations.
• • Systems with instrumentation, automation, and control.

The selection of volume, pressure, configuration, and pressurization system must be based on a hydraulic analysis and actual operating conditions.

Water hammer protection solutions may be necessary in facilities across various sectors, such as:

• • Mining.
• • Water treatment plants.
• • Drinking water systems.
• • Wastewater pumping systems.
• • Irrigation systems.
• • Industrial processes.
• • Pump rooms.
• • Extensive discharge lines.
• • Facilities with significant topographic gradients.

In all these cases, the goal is to protect the infrastructure, improve system reliability, and reduce exposure to failures caused by uncontrolled pressure fluctuations.

Protection against water hammer is not simply a matter of installing equipment on a pipeline. It requires an understanding of how pumps, valves, piping, tanks, electrical systems, and control elements interact under various operating conditions.

For this reason, a comprehensive solution may include:

• • Data collection and validation.
• • Hydraulic modeling.
• • Transient analysis.
• • Definition of critical scenarios.
• • Design and sizing of the solution.
• • Manufacturing and supply of equipment.
• • Instrumentation and automation.
• • Installation and connection.
• • Testing and commissioning.

At VOGT, we develop solutions to protect pressurized systems against water hammer, taking into account the hydraulic, mechanical, and operational characteristics of each project.

Our scope may include the analysis, design, manufacture, supply, automation, installation, and commissioning of hydropneumatic tanks and damping systems, integrating the components necessary for reliable operation.

Assessing hydraulic transients in advance allows you to identify risks, protect assets, and improve the operational continuity of your facilities.

Do you need to protect a pressure line against water hammer? Learn about our hydropneumatic tank solutions and their main applications.