Water Hammering

our engineer searching for water hammer in the pipework

What is a water hammer?

Did you know that a water hammer in the plumbing system can cause banging noises even after the tap is turned off? It is time to investigate before any serious plumbing issues arise.

The banging noise is the pipeline moving between the joints, the banging pipes touching each other or hitting the wall.

Why do you have a water hammer?

The water hammer is caused by the main’s cold water by putting pressure on your plumbing system. In simple terms, water hammer arrestors the high water pressure that flows in your pipeline, and when you close your tap this pressure creates a shock wave and makes noises.

If you hear this BANGING noise for the first time, you will not recognise it. Your pipework starts to rattle. But you can’t decide if the noise came from the roof, from inside the walls or under the floor. This loud banging noise is called a water hammer shock wave or other names for hydraulic shock.

These are a few sources that can cause water hammer:

  • Air in the system
  • Losen pipework
  • Ball or float valves are faulty
  • Solenoid valves
  • Stopcock
  • Washing machine valves
  • Fit a pressure-reducing valve
  • Taps and outlets

Why do you have a water hammer or hydraulic shock?

There are many reasons we have to talk about. A water hammer occurs when the flow velocity of water in your pipes changes direction or something stops the water flow instantaneously. Normally you hear this BANG when you close your kitchen tap or close the shower mixer. When you close one of the taps the pipework bangs against the wall or hits each other.

Another time the water hammer could occur is during the night. When no one uses the water in your streets, the water pressure increases in your home and is rattling. The best thing to start with is to fit a pressure-reducing valve before the cold water enters the house.

If you think that this water hammer will suddenly go away in a few days, we have to disappoint you, because it will just get worse. It can cause water leaks and damage to your property.

Find a local plumber who can help you with water hammer issues.

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What can cause a water hammer?

1. Air pockets in the system?

Don’t mix an air pocket with an airlock in the system. An airlock will sully stop the water flowing into your taps.

Air pockets can cause a banging sound. But this is happening straight after you open one of the taps. The air starts to flow with the water and hits the pipe wall making a noise. To remove the air pocket you have to flush through the system properly and in some cases, the pipe needs to be cut so the trapped air can be released and the system flushed. Installing automatic air vent valves can prevent water hammers. This can be installed at the highest point where the pipework is running.

An example where you can fit the automatic air vent is the hot water cylinder’s highest point of the water supply pipe that feeds the taps. After you have done any plumbing job, make sure you fill your system slowly to prevent air trapping in the water supply pipes. Also, open the taps to release the air from the system.

our plumber checking the water systems

2. Washing machine valves

The washing machine valves can cause a water hammer! How? The valve can close very quickly and stop the water flow. In simple terms, the water hits the valve inside the wall and makes a bang. You can try to turn the valve by half turn and this can release some pressure. This is not the best solution but only a DIY option. Another option is you increase the washing machine water inlet pipe size. The water will slow down in a bigger size pipe.

3. Closing Solenoid Valves

These valves are operating electrically and close the water instantaneously. This is a shock to the pipework causing the water hammer. An easy DIY solution is to fit a flexible pipe in the pipes that can absorb the shock waves and pressure change. A proper fix for this job will be an expansion vessel installation.

Are you asking where can you find a solenoid valve on your property? Well, dishwashers and washing machines are operated by a solenoid valve. When the appliance needs a water supply, the board is sending a signal to the valve to let water in or close it immediately.

the plumber locating the water hammer problem

4. Water hammer arrester

Sometimes it works. We can not leave it out of our guide. It works but it is not the best option. We speak from experience when we fitted a water hammer arrestor and didn’t work. It only works if the problem is not so bad. We would rather put an expansion vessel for a long-term solution.

5. Pipework is not secured

Old plumbing systems in the UK are not secured, especially under the floorboard. This is one of the biggest factors when you realise you have a water hammer, pipes are hitting each other. To fix this it is an easy job by fixing the pipework with clips to the wall. The hard part is that sometimes you have to cut up the floorboard and climb underneath. Same option if the pipes are banging inside the wall. The wall needs to be cut and the loose pipes will need to be fixed.

6. Pressure-reducing valve installation

This is the best option to start to fix the problem to reduce water hammer. Fit a pressure-reducing valve on the main water, supply line and pipe, before the water reaches the appliances. Don’t forget to also install a stopcock before and after the reducing valve just in case you have to replace the valve in the future, you can do it in 5 minutes. While you doing this installation, you can also fit a limescale reducer.

locating water hammer in the piping system

7. It can be the tap

Old taps where you had to turn the handle two times before the water shut off it is less likely to cause a water hammer. It is because the water can drain from the system and slow down while you turn the tap off. Modern mixer tap turns off quickly and the water hits the tap body making noises.

8. Your air chambers are blocked

You can see this in the modern water system. You might don’t have this in your system so don’t start to look for it. This air chamber helps to reduce the shock and pressure wave in the pipework after you close the tap. When the air chamber starts to fail, the water will replace the air causing water to hammer. If the air chamber is not blocked, then you can easily shut off the water, and drain the system by opening the tap, and the air chamber will fill up with air again.

9. Old stop valves

Your 15-year-old stop valve can also cause this noise. This can happen when the stop valve has loosened washer glands. The water flows through the valve and rattles the handle.

10. Water tank ball valves

Water wave? Have you heard about this? Your water tank in the loft starts to fill up, the ball valve is starting to close. But sometimes the ball valve (what is controlling the water pressure) closes, falls, and opens again. If you have only a plastic water tank the water will make waves and push up and down the pipe straps the ball valve and cause a water hammer.

If you install a water pressure reducer this will help you maintain the constant pressure in the whole water system. Make sure you install a plastic water tank that is reinforced by a metal frame.

our engineer installing check valves on the system

How to fix a water hammer?

  • Make sure all your pipework is fixed properly to the walls and floors.
  • In some places, you have to fit a copper pipe expansion joint, this will prevent water hammer.
  • Install a water hammer arrestor. But our best advice is to always fit a potable water expansion vessel on the pipework. The expansion vessel can deal with higher water pressure and you can avoid banging noises.
  • Fit a pressure-reducing valve.
  • Use pipe insulation around the pipes which can absorb the water hammer and pipe expansion. Pipe expansion happens when cold or hot water flows in the pipes and increases the pipework by a few centimetres or meters depending on the pipe materials.
  • Sometimes just leave the job for a professional plumber
  • Choose a solenoid that is closing slowly.
  • Install a water pressure regulator

You can install a copper air chamber.

The idea behind the air chamber is when the water is suddenly shut, this is a pressure surge the air chamber will absorb the high pressure.

Install a mechanical water arrestor

The shock arrestor is working similarly to the air chamber but the spring reduces the shock wave. This is. more expensive to install but it will help to resolve the issue.

Frequently Asked Questions

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