Do you hear the bang of a water hammer when you turn a tap off, flush the toilet, or run the dishwasher or washing machine? Does the sound wake you in the night or make you jump in the day? Do you want to know how to fix water hammer noise? There are several reasons for that bang and the pipe noise that comes with it, but it is possible to stop the noise.
How to Fix Water Hammer and Quiet Noisy Pipes: Reducing the water pressure, securing water pipes, and insulating pipes where they touch anything may solve the noise. Installing water hammer arrestors or air chambers, or repairing waterlogged air chambers may solve the hammer bang. However, replacing a faulty shower cartridge, changing a worn-out faucet, or a broken faucet check valve spring could be your solution.
In this article, we’ll explain what a water hammer is and explore what can cause a water hammer to occur. We’ll also look at seven ways to fix a water hammer and the pipe noise that it creates. After reading this article, you should know more about water hammers and how to quiet them.
Contents (Jump to Topic)
- What’s a Water Hammer?
- What Causes Water Hammer?
- How to Fix Water Hammer
What’s a Water Hammer?
A water hammer is also known as hydraulic shock. It occurs when the flow of water is shut off suddenly, causing the water to rebound off the valve that stopped the flow. The reversal or rebound creates a vacuum or suction that pulls the water back to the valve, making a ‘bang.’ The water repeats the motion and sound with lessening force until energy is used up. Think of a slinky that bounces up and down until it’s used up all the ‘spring’ energy.
Image courtesy of Mountain Empire Community College
The force of the water against the valve can damage pipes and joints of a water system, including connected appliances, faucets, and even the hot water tank. The sudden stop of the water and the back and forth motion also makes plumbing pipes move, causing them to rattle, vibrate, thump, and squeak. So, a water hammer can make itself heard and felt throughout the whole plumbing system of a home.
What Causes Water Hammer?
A water hammer, or hydraulic shock, happens when a valve shuts water flow off quickly or suddenly. This can occur when a faucet is shut off, especially lever or handle styles versus twist knobs. They are easier to close quickly. A filling toilet may also cause a bang when the valve mechanism in the tank closes.
Dishwashers, washing machines, and some water heaters can cause a water hammer to bang and rattle through the plumbing pipes. They have solenoid valves that electronically open and close to control the water filling flow. When the appliance has the required amount of water, it shuts in a split second, stopping the flow in an instant, sometimes with a bang.
The resulting pressure wave reverberates through the plumbing system unless it has something to absorb the energy. The force can cause pipe connections to leak. It can also damage tap valves, toilets, water heaters, dishwashers, and washing machines. So it’s not just an irritating noise; it can create the need for costly repairs
How to Fix Water Hammer
A water hammer problem may be an easy or complex repair, depending on what is causing the noise. However, most can be done by a home handyperson with some plumbing knowledge and tools. Here are 7 ways of how to fix water hammer noise.
1. Fix Waterlogged Air Chambers
Many homes built before the 1960s, and some built afterward, had air chambers located on the hot and cold water lines ahead of each tap. They were often made on-site by adding an upside-down ‘T’ joint to the line inside the wall.
A capped length of pipe, at least 12 to 18 inches long and the same diameter as the water pipes was inserted into the upward joint. The chamber may be visible inside unfinished walls in basement utility rooms or the unfinished side of basement bathroom walls.
When the water plumbing system was charged with water, the leg of the ‘T’ would ‘pressurize’ with trapped air. Hydraulic shock is caused by water being unable to expand since water isn’t compressible. However, the air trapped in the capped portion of the ‘T’ near the tap is very compressible, allowing the water to expand into the space and eliminating the water hammer.
Over time, the pipe air chambers can fill with water, resulting in a water hammer bang. So if you’ve only just started to hear a bang, this is likely the cause. Draining the water pipe will empty the air chamber of water too. When the system is filled with water again, the chamber is again filled with trapped air, and the hammer shouldn’t reoccur.
To drain the chamber, shut off the water at the valve on the feed line to the location where the hammer noise happens. Some valves have a drain port on the bottom or side that will drain water too. Open the faucet, flush the toilet, or disconnect the appliance to drain the water.
The water in the air chamber will drain out too. With the water out, the chamber will refill with air. Turn the tap off and open the shut valve to recharge the line with water. It will sputter to remove excess air, but trap the air in the chamber. The hammer should no longer occur. You will have to do this for both hot and cold supply lines.
If there isn’t an accessible shut-off valve on the line, or the air chamber is below the tap, you will have to turn off the main shut-off valve where the water enters the structure. With the supply closed, open all tap valves beginning in the basement and working upward, floor by floor to drain the whole house.
Remember to open any outside faucets too. You may want to connect a hose to move the water away from the structure. Once the water is all drained, open the main shut-off valve and let the water push the excess air out. Close the taps once they stop sputtering, beginning at the top floor (furthest from the shut-off) and working down.
2. Reduce Water Pressure
Water pressure can be responsible for many plumbing noises, including water hammer. According to most building codes, the residential pressure should be less than 80 PSI. Higher pressure force can result in noise, leaks at joints, and even pinhole leaks in the pipes themselves. The recommended pressure is between 40 and 60 PSI.
If the hammer bang only occurs at one tap or appliance, check the pressure at that outlet using a water pressure gauge. They are available at most building and hardware stores and are priced reasonably, or borrow one. It needs to be threaded onto the faucet or appliance hose, so remove the hose from the appliance or aerator from the tap. Thread the gauge into place, and open the tap or valve. If the pressure is greater than 60 PSI, it should be reduced.
To reduce the water pressure, you need to locate the pressure regulator. It is commonly located between the main water shut-off valve and the water meter where the service enters the building. The regulator may even have a pressure gauge that you can check too. If there isn’t a regulator located on the main water feed, you’ll need a plumber to install it – especially if there is a water meter on the line. The plumber will also adjust the water pressure.
If there is a pressure regulator, locate and slowly turn the main water shut-off valve to the closed position. Locate the adjustment bolt or screw, and the locking nut. Loosen the locking nut 1/4 turn at a time until the adjustment bolt or screw will rotate. Turn the adjustment counter-clockwise to decrease water pressure, and clockwise to increase it.
Do the adjustment 1/4 rotation at a time, checking the pressure on the gauge at the tap or the regulator. It’s easier if there is a helper to relay pressure gauge readings if not on the regulator. If the pressure is still too high, rotate another 1/4 turn – and repeat until it is less than 60 PSI. Secure the adjustment nut or screw by tightening the locking nut.
Remove the pressure gauge from the tap, reattach the aerator, and run the water. Shut the tap off quickly. If the water hammer was due to high water pressure, it should be silent. If it is as it was, attempt a different solution.
3. Install Water Hammer Arrestors
A water hammer or hydraulic shock can cause pipes and plumbing joints to leak and damage faucets and appliances since it produces hundreds of PSI of pressure. Installing a water hammer arrestor at the faucet, toilet, or appliance where the noise originates is a good solution. If the ‘bang’ is generated from more than one location, consider an arrestor for each location.
A manufactured water hammer arrestor is similar to the air chamber used before the 1960s, but with some modifications. It has fittings that thread onto a tap, toilet, or appliance hose, and a manufactured air chamber with a diaphragm or piston in a sealed chamber. When a valve shuts quickly, the ‘hammer’ energy expands into the arrestor.
The energy pushes the diaphragm or piston against the more compressible air, absorbing the energy and silencing the hammer bang. Most faucets require two arrestors, one for the cold water line, and one for the hot water.Identify the diameter of the flex-pipe link to the noisy fixture. The water hammer arrestor coupling connection diameter must match to thread into the fixture (toilet, faucet, dishwasher, washing machine) and the supply line between the shut-off valve nearest it. Most household taps and appliances require an ‘AA’ hammer arrestor size – there are different sizes based on placement and number of fixtures supplied on an individual water line.
Turn the water off at the nearest valve. Note the number of turns for reference.
Flush the toilet or open the sink tap to depressurize the section of the water pipe, and remove as much water from it before beginning work. Place a bucket or bowl under the connection to collect water.
Use channel lock pliers, a wrench, or plumbers tool to loosen the coupling nearest the fixture. There may be two back-to-back nuts that are tightened into each other, or only one. You only need to loosen the flex-pipe coupling so it can be removed.
The water will begin the drain once you loosen the connection. It shouldn’t spray unless under pressure – check the shut-off valve if it does spray. Disconnect the flex-pipe only at the fixture end.
Tighten the fixture if it becomes loose.
Wrap plumbers tape around the metal threads of the arrestor and fixture connection – 4 times around should be enough. Plastic to plastic doesn’t require taping.
Thread the arrestor to the fixture connection, and tighten. Check that the fixture remains aligned correctly.
Thread the flex-pipe to the arrestor and tighten. Position the arrestor air chamber in the desired direction before the final tightening.
Slowly turn the water valve back on. There may be a vibration as air in the line works to escape. You may need to open other taps in the house to remove trapped air. Once the air is bled out, open the valve fully and check for leaks. Tighten if possible or disconnect, drain, reapply more tape, and reconnect.
Flush the toilet or turn the tap on and off several times. The thump or bang of the water hammer should be gone.
A whole home-arrestor would be installed between the pressure regulator and the plumbing service shut-off valve to protect the home’s plumbing from hydraulic shock on the delivery end. It works the same way but must be large enough to absorb a greater shock pressure. It would not provide much protection within the household plumbing system as it needs to be close to the source generating the force.
4. Change Worn Out or Broken Faucet Check Valve Spring
I had an issue with knocking noise in the upstairs bathroom behind the shower cabin. The plumber came, opened the wall, and installed an additional arrestor…still the same.
He then installed a big arrestor in the basement on the main water intake pipe….still the same knocking noise. In the end, he called the manufacturer of shower faucet (it was under warranty), they sent a tech guy who changed the check valve springs in the faucet, and finally, the knocking noise was gone.
Check valves allow fluid or gas to flow in one direction. Sump pumps and wells often have a diaphragm or ball check valve to prevent water flow reversal. They have to be installed in a more vertical pipe as gravity helps close them.
A spring-loaded valve doesn’t require gravity, pressure from the water flow ‘cracks’ the valve open, and the spring closes it when the flow is shut off at the tap. Any hydraulic shock is contained by the check valve, preventing the shock force or backflow from damaging the plumbing pipes.
A spring check valve has an inlet port to allow water in and an exit port, so they need to be installed in the direction of water flow. They have a piston, spring, and an O-ring seal.
When a tap is open, the water flow pressure pushes against the piston, compressing the spring and ‘cracks’ the seal, permitting water to flow past the seal. When the tap is closed, the loss of pressure allows the spring tension against the piston to reseat the seal and close the valve.
Spring-loaded check valves can be installed near faucets or appliances connected to the plumbing system. Some fixtures have them built-in too. The valves are manufactured in different sizes, connection types, materials, and for a wide range of ‘cracking’ pressures. The spring determines the ‘cracking’ force needed to compress it, and open the valve seal.
The ‘cracking’ pressure is the minimum force or pressure required to crack open the seal and allow water to flow. A check valve needs to match the water pressure of the water flow to be effective. An incorrectly sized valve can cause a water hammer. Additionally, seals and springs wear out, which can also lead to hydraulic shock.
To replace a worn or damaged check valve order or purchase a check valve repair kit to match the faucet and water pressure.
A valve replacement kit will have one or two valves, springs, and washers depending on the type of faucet.
Turn the water supply off to the faucet and open the tap to relieve water pressure.
Remove the handles or knobs with a screwdriver, hex key, wrench, or special tool supplied with the faucet. With the handles removed, remove the cover plate.
The red arrows point to the two spring check valves.
Use a wrench to remove the check valves. Assemble the new valves and thread them into place. Some valves may require plumbers tape wrapped around the threads of the replacement; others may have a tube of sealant to apply to the threads. Follow the manufacturer’s instructions to avoid leaks.
Before replacing the cover plate, turn on the water supply and open the tap to check for leaks. Some air may sputter, but not much. When you shut the tap off, the water hammer should be gone. Replace and seal the cover plate and put the handles on.
5. Change Bad Shower Cartridge
A shower cartridge diverts the water from the bath spout to the showerhead. A faulty or worn shower cartridge may drip, not seal tight, so water comes out the shower head and spout, or close with the bang of a water hammer. Replacing the shower cartridge takes a couple of tools and some DIY patience.
Turn off the water supply to the hot and cold lines for the shower or tub. Open the faucet to drain and depressurize the tap. Close or cover the shower drain. A folded towel or pad will also protect the tub or stall from dropped tools or parts.
Remove the tap handle with the correct tool so as not to strip the fasteners. Remove the cover plate or ring that covers the cartridge. You may need to cut the caulking seal.
The cartridge is held in place by a nut that needs to be removed using the correct tool. Use WD40 or another spray to lubricate for easier removal. With the nut removed, grasp the cartridge and gently pull it out.
Water or adjustable pliers may help. Take the cartridge to get the appropriate replacement unless you have the model and serial number of the faucet.
Install the new cartridge. If it sticks, use petroleum jelly or WD40 to lubricate for easier insertion. Wrap the fixture threads with plumbers tape, and thread the nut into place. Tighten with the appropriate tool.
Turn the water supply on and check for leaks. When the tap is closed, the water hammer should be gone. Replace and seal the cover plate or ring, and reattach the handle, and clean up.
6. Secure Loose Water Pipes
Loose pipes can vibrate and thump with changes in water pressure. Check that the brackets that fasten pipes to structural framing members haven’t loosened. Replace metal clamps with plastic or nylon, and use screws not nails to fasten them.
Wrap the pipe with electrical or plumbers tape, inner tube, or a piece of rubber hose where the clamp will go to minimize noise. Pipes should be secured every 6 to 8 feet. If they are supported but still make noise, add fasteners to support every 2 to 3 feet. Clamps should be tight, yet still allow pipes to expand.
7. Use Pipe Insulation to Cushion Water Pipes
Pipes that are supported loosely by cross braces or pass through walls or structural pieces may also bang, thump, or rattle as water moves through them. Wrap the pipes with pipe foam to stop the noise. Where pipes come through walls, wrap them with foam to fill the hole, and prevent pipe movement noise and the transfer of sound through the hole.
Decreasing water pressure, fastening or wrapping loose pipes, installing water hammer arrestors, and replacing faulty check valves and faucet cartridges are different ways to quiet plumbing noise. Hopefully, you have a better understanding of how to fix water hammer and quiet noisy pipes.
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