Water Hammer Fix
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How to prevent and eliminate water hammer in home water heating systems? What causes the problem, what are the symptoms and how to fix it. What is the water hammer arrestor, how does it work and how to install one?

What is water hammer?

It is not uncommon for water heating and plumbing system to generate loud noise such as banging and thumping, especially when water stops or changes directions suddenly. This problem is known as water hammer, a phenomenon related to the hydraulic shock waves, which can cause vibration of plumbing pipes when they strike against each other or wooden beams.

What can cause water hammer

The problem can be found in both new and old houses and no matter of the type of the plumbing; copper, CPVC or steel. Depending on the pipe type, the noise level varies. 

Valves. What can cause water hammer to take place are a single lever faucet and a faucet with the solenoid valve, also washing machines and dishwashers, because they are equipped with the automatic valves that close fast.

Pressure. The problem can also occur when the water pressure from the main supply pipe is too high. Normal pressure is from 30 to 60 PSI and to avoid damages on the heater’s elements due to extreme pressure; it is recommended to install a pressure reducing valve.

Problems caused by water hammer

  • Loud banging or thumping noise
  • Collapsed flue tube on gas heaters
  • Deformation on the top of the heater
  • Expansion in the tank shell
  • Damages to piping, TPR valve, water meter, pipe joints

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Troubleshooting and how to stop water hammer

There are several approaches on how to prevent or eliminate water hammer.

  1. The simplest solution for this problem is to turn the tap off slowly so water inside the plumbing system can slow down gradually.

  2. Secure the loose pipes. Install or tighten any loose pipe straps that secure the tubing to the wooden frame. You can also put a pipe sleeve insulation onto the pipes. This is possible only there where the pipes are exposed and not hidden behind the walls.

  3. If the above suggestions do not solve the problem, you might have to install a device called arrestor.

  4. There are some suggestions from the manufacturers, such as Bradford White, that the problem can be solved by installing an expansion tank and pressure relief valves with the setting at 25-50 pounds less than the TPR valve on the heater.

How does the arrestor work

Water hammer arrestorWater hammer arrestor

A water hammer arrestor, also known as an air cushion or air chamber, is a simple device where inside of its cylindrical body is pre-charged and sealed air chamber. The chamber is divided by the sliding piston. A side which connects to the plumbing is filled with water, while on the other side of the piston is air. Since the chamber is sealed, there will be no air or water leak. While the sudden water pressure increases, the sliding piston moves toward the air chamber compressing the air, so the vibrations will dissipate into this cushion of air, protecting the system from high-pressure shocks.

The water comes from the side which is connected to the plumbing.

The arrestor can also fail. The air chamber can become filled with water reducing its performance. Also, it can get clogged with the accumulated mineral deposits and debris, requiring proper cleaning.

Note: The air is factory charged. Some models are rechargeable, and some are not.

How to install an arrestor?

An arrestor for home use is easy to install. The arrestor should be installed near the water heater, as close as possible to quick-closing valves, and on the same pipe where the hydraulic disturbance appears. The arrestors are available for standard pipe sizes of ½” and ¾” or larger diameter. Due to the smaller size of the device, it can be easily installed inside a wall.

Arrestors can be installed in new and existing homes and plumbing systems, positioned horizontally, vertically or at any angle. Some models are designed for threaded applications, compression installation, with quick T-connect, brass adapter, for PEX and copper installation and other.

Follow the installation tips below:

  • Turn off the water supply.
  • Drain the pipe that makes the noise and where the arrestor will be installed.
  • If you have copper pipes, cut the pipe and prepare for soldering.
  • Connect the pipes to a T-fitting.
  • Screw the arrestor on the threaded T fitting.

Required tools

  • Adjustable wrench
  • Pipe wrench
  • Pliers
  • Torch
  • Solder
  • Cutting tools

Water hammer does not occur only in water heating systems. It can happen when running a washing machine, dishwasher or when flushing a toilet. The arrestors are the most common way of the water hammer repair and should be installed on the pipe where it occurs.


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