Water Hammer Effect

Water Hammer Effect

Water hammer effect is a common phenomenon that can occur in plumbing systems, causing loud and unsettling banging or knocking noises.

This article will delve into the causes and potential consequences of water hammer, as well as explore ways to prevent and fix this problem. Whether you have experienced water hammer in your own home or are simply curious about this dynamic hydraulic occurrence, this article will provide valuable insights and information.

Water hammer formula

Here is an explanation and formula for calculating water hammer in a piping system.

Water hammer is a common phenomenon that occurs in piping systems when there is a sudden change in flow velocity or a sudden stoppage of flow.

This sudden change in flow can create pressure surges, causing potentially damaging impact forces on the piping, valves, and other system components.

The formula for calculating water hammer is:

P = (pV/u) x L x K

P = pressure surge (in pounds per square inch, or psi)
p = density of fluid (in pounds per cubic feet, or lb/ft^3)
V = change in velocity (in feet per second, or ft/s)
u = speed of sound in fluid (in feet per second, or ft/s)
L = length of pipe (in feet, or ft)
K = coefficient of water hammer

The coefficient of water hammer (K) varies depending on the type of valve, velocity of flow, and pipe material. It can be determined through experiments or found in tables provided by manufacturers.

In order to use this formula, it is important to understand the conditions that can lead to water hammer. These include sudden changes in flow velocity due to valve closures, pump start/stop operations, and changes in elevation or slope of the piping system.

To prevent water hammer, it is important to ensure proper design and installation of piping systems. This includes the use of appropriate valves, flow control devices, and proper support and anchorage of pipes.

In addition, it is important to consider the potential for water hammer during the design phase and to incorporate measures such as surge tanks and air chambers to reduce the pressure surge.

Pressure Rise Due to the Gradual Closure of the Valve

In the field of hydraulic engineering, the phenomenon of pressure rise due to the gradual closure of a valve is a crucial aspect to consider in the design and operation of water systems. As a civil engineer, it is essential to understand the mechanics behind this occurrence and its impact on the overall system.

When a valve is slowly closed, the flow of water through the pipe is restricted, leading to an increase in pressure. This is because the velocity of water decreases as it flows through a smaller opening, causing a build-up of pressure in the pipeline.

This pressure rise is directly proportional to the rate at which the valve is being closed. As the valve nears complete closure, the pressure increase becomes more significant.

The pressure rise due to the gradual closure of a valve has various implications on the system. If the system is not designed to withstand the sudden surge in pressure, it can result in burst pipes, leakage, or damage to other components. Additionally, this phenomenon can also cause water hammering, a sudden and powerful shock wave created by the rapid change in pressure, leading to potential damage to the system.

To mitigate these issues, engineers use various techniques to control the pressure rise. One such method is the installation of pressure relief valves, which automatically release excess pressure to prevent it from damaging the system.

Another approach is to incorporate an adjustable valve closure mechanism, which allows for a slower and more controlled closure of the valve to reduce the impact of pressure rise.

Pressure Rise Due to the Sudden Closure of the Valve

As a civil engineer, I have studied and analyzed the potential risks and consequences of various scenarios in fluid mechanics. One such scenario is the sudden closure of a valve in a fluid flow system, which can result in an increase in pressure

This increase in pressure, commonly known as pressure rise, can have significant effects on the surrounding infrastructure and equipment.

When a valve is abruptly shut, the fluid flow through the system is disrupted, leading to an immediate halt in the movement of the fluid. As a result, the fluid in the system continues to exert pressure on the downstream side of the valve, while its momentum causes the fluid to compress and create a pressure wave in the upstream direction.

This pressure wave, also known as a water hammer, can cause a sudden spike in pressure, which can reach several times the initial pressure in the system.

The pressure rise due to the sudden closure of a valve can have various impacts on the system and its components. The most common consequence is damage to the infrastructure, including pipes, valves, and other equipment. The sudden increase in pressure can exceed the maximum operating pressure of these structures, leading to ruptures, leaks, and potential failures.

The pressure rise can also result in significant noise and vibrations, which can be a safety hazard to workers and the public. Furthermore, it can cause severe stress on the valve and its components, leading to potential failures and malfunctions in the future.

To mitigate the risks associated with pressure rise, it is crucial to carefully select and install appropriate valves that can handle the anticipated pressure fluctuations.

Additionally, the design of the system should also consider the fluid’s velocity and flow rate to prevent excessive pressure build-up. Regular maintenance and testing of the valves and the system can also ensure their proper functioning and reduce the likelihood of sudden closures.

Water Hammer Effect Relieving Devices

Water hammer effect is a common occurrence in water supply systems, especially in high pressure pipelines. It is characterized by a sudden surge of pressure caused by rapid changes in flow rate, which can result in damaging impacts on the pipes and associated equipment.

To prevent the negative effects of water hammer, engineers have developed various relieving devices that can dissipate the excess pressure and protect the system.

One of the most widely used water hammer effect relieving devices is the air chamber. It is a simple device that consists of a vertical pipe connected to a water supply line. The air chamber is installed at a high point in the system to provide a cushioning effect against water hammer. As the water flow in the pipeline changes, the air in the chamber compresses, absorbing the excess pressure and preventing water hammer.

Another effective device for relieving water hammer is the surge tank or surge vessel. It is a large tank placed in the water supply system, usually at low points or bends in the pipeline.

When the water flow in the system changes suddenly, the surge tank takes in the excess pressure, reducing the effects of water hammer. The water in the tank is then released slowly back into the system, bringing the pressure to a steady state.

Apart from air chambers and surge tanks, hydraulic accumulators are also commonly used water hammer effect relieving devices. They are essentially large cylinders filled with air or gas, connected to the water supply system. The pressure in the accumulator acts as a cushion, absorbing the surges in water pressure and preventing water hammer.

In addition to these commonly used devices, pressure relief valves and check valves can also help to alleviate water hammer. Pressure relief valves are designed to open when the pressure in the system exceeds a certain limit, while check valves allow water flow in one direction and prevent backflow.

Both of these devices can help to regulate pressure and prevent water hammer from occurring.


In conclusion, the Water Hammer Effect can have damaging effects on a plumbing system if not properly addressed. It is important for homeowners and building managers to be aware of this phenomenon and take necessary precautions to prevent its occurrence. Regular maintenance and timely repairs can help mitigate the risk of damage from water hammer. Additionally, the use of water hammer arrestors can provide a long-term solution to this problem. With proper knowledge and proactive measures, we can ensure the longevity and efficiency of our plumbing systems. Let us be mindful of the Water Hammer Effect and protect our homes and buildings from its detrimental impact.

FAQs – Water Hammer Effect

What is the Water Hammer Effect in plumbing systems?

The Water Hammer Effect, also known as hydraulic shock, refers to the loud banging or knocking noises caused by sudden changes in water flow or pressure within pipes. This dynamic occurrence can potentially lead to damage in plumbing systems.

What causes the Water Hammer Effect?

The Water Hammer Effect is primarily caused by abrupt changes in water flow velocity, such as sudden valve closures, pump failures, or rapid changes in flow direction. These changes result in pressure surges that create shock waves within the pipes.

How can I calculate the Water Hammer Effect in a piping system?

The formula for calculating water hammer is: P = (pV/u) x L x K, where P is pressure surge, p is fluid density, V is change in velocity, u is speed of sound in fluid, L is length of pipe, and K is the coefficient of water hammer.

What are the potential consequences of the Water Hammer Effect?

Water Hammer can lead to physical damage to pipes, valves, and fittings due to the powerful shock waves. It can also cause disruptions in water flow, fluctuations in pressure, and even contamination of water. Additionally, mechanical equipment connected to the system may suffer from wear and tear.

How can water hammer be prevented or mitigated?

Water Hammer can be prevented by designing and installing proper piping systems. Techniques include incorporating air chambers, surge tanks, and pressure relief valves. Slower valve closures, reducing water velocity, venting air from pipes, and maintaining constant water pressure are effective preventive measures.

What is the purpose of an air chamber in relieving water hammer?

An air chamber serves as a relieving device by providing a cushioning effect against water hammer. Installed at high points in the system, the air chamber allows air to compress as water flow changes, absorbing excess pressure and preventing the damaging effects of water hammer.

How does a surge tank help in mitigating water hammer?

A surge tank, or surge vessel, is a large tank placed strategically in the water supply system. It absorbs excess pressure during sudden changes in water flow and releases water back into the system gradually, stabilizing pressure and reducing the impact of water hammer.

Are there other devices that can relieve water hammer?

Yes, hydraulic accumulators, pressure relief valves, and check valves are commonly used devices to relieve water hammer. Accumulators act as large cylinders filled with air or gas, providing a cushion against pressure surges. Pressure relief valves open to release excess pressure, while check valves prevent backflow.

How can homeowners protect their plumbing systems from the Water Hammer Effect?

Homeowners can protect their plumbing systems by being aware of the Water Hammer Effect and taking preventive measures. Regular maintenance, timely repairs, and the installation of water hammer arrestors can contribute to the longevity and efficiency of plumbing systems.

Why is it crucial for civil engineers to understand and address the Water Hammer Effect?

Civil engineers play a crucial role in designing and implementing water supply systems. Understanding and addressing the Water Hammer Effect is essential to prevent potential damage to infrastructure, ensure system efficiency, and protect public safety.

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