What is water hammer and how can it be avoided?
Pressure fluctuations in water distribution systems can cause a phenomenon known as "water hammer". The shocks generated by water hammer can eventually damage pipes and cause significant damage to plumbing. Where does this phenomenon come from? What are the consequences for a plumbing system? And above all, what can be done about it? Our expert tells you everything!
What is water hammer?
Water hammer is an overpressure phenomenon that occurs when the speed of a fluid in a pipe network suddenly changes. It occurs, for example, when a valve or tap is closed quickly, or when a pump is stopped. When a valve is closed, the inertia of the moving water is suddenly slowed down. This generates a high pressure and a shock wave. This overpressure wave travelling through the pipe system then results in vibrations and a thud, reminiscent of the sound of a hammer blow.
The dynamic change in pressure can have serious consequences for your sanitary installations, fittings and pipes. In the case of large installations, it can even lead to a pipe bursting due to the amount of liquid in motion.
What are the causes and consequences of water hammer?
Water hammer, a physical phenomenon with various causes
The causes of water hammer are varied but are still common when a hydraulic installation is shut down. It generally occurs when a valve at one end of the pipe system is suddenly closed.
This is because when you close a valve or tap, the water continues to flow at a certain speed through the pipes. The rapid change in fluid velocity generates a high pressure and a shock wave in the pipe. This is also known as hydraulic shock. Due to the inertia of the fluid, the flow velocity of the fluid can no longer adapt to the new situation. As a result, the fluid deforms, leading to dynamic pressure changes. The elastic energy carried by the propagation of hydraulic waves can cause serious problems and damage your installations. If the pressure is high enough, water hammer can cause a pipe or valve to break.
Water hammer is a common occurrence. In a domestic plumbing system, water hammer can occur when the water supply to a washing machine or dishwasher is cut off, producing a characteristically loud noise accompanied by vibrations.
Harmful consequences for your sanitary installations
The consequences of water hammer are not only harmful, but can also be dangerous.
Water hammer is in most cases hydraulic, i.e. caused by a sudden change in the flow of a liquid. But it can also be thermal, caused by the temperature difference in the pipes between the hot water vapour and the cold pipe. A condensate is then formed. This generates air draughts in your pipes.
Air vents can be installed in pipe systems to resist the adverse effects of water hammer. The automatic air vent is used to remove trapped air from heating and cooling systems.
Other factors, such as lime deposits, the accumulation of micro-organisms and corrosion residues, or pump failure, can also cause and increase water hammer.
In the long term, water hammer can lead to material damage such as :
- Deformation or breakage of water pipes;
- Leakage, through the loosening of fittings;
- Rupture of expansion tank membranes.
It is therefore advisable to avoid them before damaging your plumbing installation, and more generally your home.
In the case of circuits intended to supply hydraulic power plants, for example, the kinetic energy must be stopped when the water cannot be isolated with a valve.
Because the water flow in the pipes and tunnels of hydroelectric plants is very high, the energy can be extremely dangerous. The force caused by a water hammer can be comparable to an explosion. Networks carrying hazardous fluids are given special attention during design, construction and operation.
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How can I stop water hammer?
Water hammer is never a good sign for your plumbing system. The damage to your pipes, pumps or sanitary fittings is not always visible. It is even common for a fairly long period of time to pass before a pipe breaks.
To prevent damage to your plumbing and heating system, there are simple measures you can take to eliminate or reduce water hammer.
Install a pressure regulator
Installing a pressure regulator at the inlet to your home's water system reduces the pressure of the water supply as it passes through the pipes. This ensures that the water pressure at the outlet remains optimal and constant.
The pressure regulator protects your sanitary installation from overpressure and therefore from water hammer. It also prevents wear and tear on your sanitary fittings and household appliances such as washing machines and dishwashers.
Use slow closing speed taps
The slow-closing/opening tap, or solenoid valve, uses a device that reduces the speed of water flow and closes the tap after a predetermined time. If you notice noises in your pipes when you use a tap, then this is the solution. In addition to preventing water hammer, slow-closing taps will save you water.
Opt for an anti-pulsation or anti-hammer cylinder
The anti-pulsation cylinder, also known as the anti-hammer cylinder, is used to stop excessive pressure. There are 2 different categories to suit your home, your water needs and your sanitary installation:
- the spring water hammer arrester: it consists of a piston system that absorbs the shock wave when air infiltrates the water circuit;
- the membrane water hammer arrester: the membrane separates the air and the water, which reduces the pressure of the water in the circuit and prevents the shock wave. This system is more resistant and effective than the spring water hammer arrester.
For a water hammer arrester to be effective, it is important to position it close to the elements concerned, and to install it in a bypass and on the hot and cold water supply.
Installing a non-return valve
A non-return valve is a device that is used to control the direction of a fluid in a pipe. It can be installed at the water meter, the various drains (shower, bath, sink, etc.) or the water heater. Non-return valves are unidirectional, i.e. they allow only one direction of flow. If the liquid changes direction, the valve closes to protect the pipe network - pumps, valves, etc - from water hammer.
There are other solutions to prevent water hammer. For example, a surge chamber can be installed (mainly used in industry), or straight pipework can be modified by adding elbows or expansion bends. You can also unclog pipes by loosening clamps that are too tight, or by enlarging seals that are too narrow. Finally, you can also invest in piping elements designed for high pressures.
Sanitary fittings standards: for a long-lasting operation of sanitary installations
Professionals in the drinking water distribution sector, such as manufacturers of plumbing components, pipes and valves, are aware of the risks and potential dangers caused by water hammer.
Moreover, sanitary fittings are governed by standards and certifications that guarantee the quality and safety of the products.
To avoid this phenomenon and to market their products, manufacturers must therefore carry out tests in accordance with the standards in force. Carried out in the laboratory on hydraulic test benches, the tests simulate water hammer and check the pressure resistance of valves, taps, PE pipe fittings, sealing collars, etc. The pressure test bench allows the reproduction of water hammer in pipes and the testing of the ageing of components according to the NF EN 13618 standard.
Therefore, choosing certified and standard-compliant fittings is the first step towards ensuring the long-term operation of installations. Because a water hammer is not only unpleasant for users, but above all it is harmful to sanitary systems. Although often benign, they must nevertheless be taken seriously to avoid damaging the pipes.
