Last updated: July 7, 2021 at 13:30 pm
Hearing an alarming banging from your pipes when using your washing machine or turning off the tap? What you’re probably hearing is water hammer noise. It’s usually nothing too serious, but can be frightening when it gets too noisy.
In this article:
We will explain what water hammer is, what can cause it, and things you can do to fix it.
What is Water Hammer?
Water hammer is a noise that comes from your pipes when the water hits a blockage and stops moving. The sudden stop causes your pipes to make shaking, rattling and banging noises that can sound quite alarming if you don’t know what’s causing it.
It can be caused by something as simple as turning off a tap. The water was expecting to pour out of the tap and instead hits the closed valve at force. If you keep holding onto the pipe, you may even feel the tap vibrate in your hand.
What Causes It?
As explained above, it can be caused by anything that causes the water flow to shut off suddenly. Taps and showers can cause it, but more often, the culprit is washing machines and dishwashers. Machines can close a valve much more quickly than a human hand can, exacerbating the problem.
How to Stop Water Hammer Noise
Check Your Pipes
If you have exposed pipework, it’s worth checking if they’re loose. Pipes should be firmly fixed to the wall or your joists to prevent them from moving and banging when water flows through them. Try to move them but be gentle; after all, you don’t want a flood on your hands.
If they are clearly moving, then a trip to the DIY shop is in order. First, get brackets and reattach them anywhere that feels loose. Once that’s done, try turning on and off your taps or running your washing machine and see if water hammer is still a problem.
If all your pipes are tucked away behind the walls, then the only definite way to check it would be to start cutting holes anywhere you hear a noise. However, opening up walls is a big job and very disruptive, so it would be best to exhaust all the other options below and do it only as a last resort.
Water Pressure Regulators
Water hammer can also be caused by too high a pressure where the main water pipe enters your home. Water pressure should be somewhere between 40 and 60 pounds per square inch (psi). Any pressure above this can cause water hammer, and if it gets as high as 100 psi, it could actually damage your washing machine and dishwasher.
The way to fix this is to fit a water pressure regulator. Ideally, you should fit one at the point where the main water pipe enters your home. Locating it there should remove the need to install multiple air chambers (explained below) because it will also offer protection to appliances, toilets, and other water fixtures and fittings.
If you’re particularly DIY savvy, you may be able to check the water pressure yourself with the correct tools. You’ll need to verify how high it is before it can be fixed. Once you’ve established the current pressure, you’ll need to set the regulator to create a pressure within the normal range. As 50 psi is right in the middle, that’s probably a good choice. However, as leaks can cause a substantial amount of damage unless you’re extremely confident in your plumbing skills, it’s safer to call in a professional.
- Inlet pressure: 1.6Mpa (Max) / 232psiWater pressure: 0.05-0.8Mpa...
- Thickened interface thickened valve body: the main body molding,...
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One of the easiest ways to fix water hammer is by adding air chambers. An air chamber is a short piece of vertical piping. It is installed near a valve and acts as an air-filled cushion for the water when the valve is closed.
It may sound complicated, but if you’re careful, you can fit air chambers yourself. If you’ve successfully located the source of the water hammer and it’s restricted to one area, you may just need to fit one.
However, it may be necessary to fit them in multiple locations. However, if you feel you need air chambers to be added throughout your plumbing, then it may be better to fit the water pressure regulator described above. Plumbers will just use short sections of normal pipe, but you can buy specially made chambers.
Flooded Air Chambers
Even if you have air chambers, water hammer can still occur. Eventually, water will start to take the place of air in the air chambers, removing the cushioning effect. As there is no air left to soften the flow, the water flowing through the pipe can crash into the closed valves in its way, resulting in banging and rattling noises. Luckily, it’s easily fixed. Here’s what you need to do.
- Shut off the water at the mains using the stopcock. It’s usually under the sink in the kitchen but might be elsewhere.
- Turn on all the taps upstairs first
- If you’re in a flat, that’s all you need to do. If you’re in a house, you should head downstairs and turn on the taps there. A townhouse or a house on more than two levels, finish by turning on the taps on the lowest levels.
- Wait by the downstairs taps and when the water stops running, turn them off. On three-level homes, turn off the taps on the middle floor too.
- Then, with the upstairs taps still on, switch the water back on at mains. This will cause the water to move back throughout the system, but the air chambers will remain filled with air.
- Remember, this is not a one time fix. You need to empty your air chambers regularly to prevent the water hammer from recurring.
Water Hammer Arrestors
A water hammer arrestor creates a chamber filled with either gas or air. This chamber is sealed using either a piston or a diaphragm. You may not have heard of a diaphragm in a plumbing context before, but it’s just a flexible disc, often made of rubber, that forms a seal when placed under pressure.
An arrestor is often added at the place where the pipe or hose that supplies the water connects to a tap or shut-off valve. You would use this instead of an air chamber or pressure regulator rather than in addition to them.
- 3/4 BSP Fitting
- 3/4-Inch Female Hose Thread and 3/4-Inch Male Hose Thread
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Fitting an Arrestor
- Shut off the water. You should only need to do this for the tap or appliance where you’re fitting the arrestor rather than at the main stopcock. If you’re going to be fitting several arrestors, though, it’s probably easier to shut it off at the mains. Most appliances will have their own shut-offs. A washer will have a cold and a hot water shut-off, whereas a dishwasher will just have one for the hot water.
- Disconnect any hoses where they connect to the pipes. Have a basin ready underneath to catch the water which is still inside. In case there’s more water than you expected, have a few old towels handy, too. Either use an adjustable wrench or tongue-and-groove pliers to loosen the hose fittings.
- Use thread seal tape to tape the male end of each water inlet or shut-off valve. Wraps the tape around it tightly three or four times in a clockwise direction. Next, wrap the tape around the male threads on the water hammer arrestor, too, if it has them.
- Now it’s time to install the arrestor. This varies slightly depending on the type of arrestor you’re using. If you’re using a compression fitting, you need to place the compression ring against the inlet or valve. Once it’s in place, thread the compression nut on and tighten it up. For threaded water hammer arrestors, you’ll need to turn the female end clockwise by hand to thread the arrestor onto the valve. Once it’s secure, finish the job by tightening it with pliers. Push-fit water arrestors are the easiest of all because no tools are needed for installation. Clean the copper tubes thoroughly of any burrs. Ensure that all cuts are neat and square, then firmly push the fitting onto the pipe.
- Now the arrestor is installed, you just need to reverse your initial steps. Use your wrench of pliers to reconnect the tube or hose that supplies the water to the arrestor. Make sure the connection is fully tightened.
- Turn the shut-off valves back on slowly. Be aware that if you shut off the water at the main stopcock, your taps might splash a little before the water begins running normally again, so stand back at first. Use a torch to check that nothing appears to be leaking, and then run any appliances you’ve fitted an arrestor to. This is to check for leaks and also to see if the banging noises are fixed.
If you hear a banging noise when turning off your taps, then water hammer is a likely culprit, but there can be other causes. If you’re not sure or are concerned about following any steps, then make sure you consult a professional. It will be cheaper and less stressful for you to have them in to fix a relatively minor problem than a major disaster.