Tracing Water Hammer – Air Chamber and Water Hammer Arrestors

We get a ton of calls each year regarding vibrations in residential and commercial water lines so we thought we should explain. What is the banging that can occur in water lines? What can be done to prevent it from happening?

Well the first thing we will do is tell you is that there are a couple things that can cause vibrations in water lines and they are:

  • Appliances or equipment that have a motor that turns or churns water. A dishwasher or a house pump used to increase water pressure are two that can cause banging or vibrations.
  • Water Hammer

The solution to solving the problem of vibrations transferring along the water lines due to appliance activation is simply to install vibration isolation devices. For a dishwasher they can be as simple as having rubber pads under the unit. These rubber pads absorb the vibration from the appliance thereby eliminating the transference of vibrations and noise. On large mechanical equipment an engineer may specify both vibration isolation pads and flexible braided water connections.

The next issue and probably the most common in household plumbing is water hammer. Water hammer is the shock and the audible banging of the water piping caused by a valve or faucet being closed quickly against water flow. Picture this the water is turned on and it is going in one direction, suddenly the valve is closed off abruptly stopping the flow of water and water is not very compressible. The shock of the flow of water being stopped causes the energy to bounce back and forth along the pipe. If the proper precautions aren’t taken water hammer can crack pipe joints, loosen or break hangers and damage valves.

So How Can You Stop Water Hammer?

There are two ways actually and they are as follows:

Air Chambers : Air Chamber are usually fabricated in the field and they consist of a piece of water pipe closed on one end with a sweat cap, the lower end is attached to the water piping system. Air is trapped in the upper part of the chamber and is compressed by the shock wave caused by water hammer. The air absorbs the kinetic energy caused by the closing of the valve, as the shock lessens the air in the chamber expands to it’s normal pressure. Sometimes an air chamber can become water logged, which means the air chamber is eventually filler with water. You can recharge an air chamber by draining down the water system and refilling.

Sizing an Air Chamber : An air chamber should never be smaller in diameter than the water piping it serves. It should not be shorter than 18” long. If the Air Chamber is close to an existing shut off valve the piping of the chamber should be one pipe size larger than the piping being served.

Water Hammer Arrestors : Water Hammer Arrestors are premade mechanical devices that stop the clanging and banging of water piping. These pre-made arrestors are exceptionally useful when used with commercial dishwashers, quick closing valves, fixture controls, dishwshers etc. Pre-made water hammer arrestors are built with permanent pre-charged air chambers. These are usually manufactures with a sealed diaphragm that expands to absorb water hammer.

What Information Should You Look for When Installing Air Chambers or Water Hammer Arrestors?

  • What is the size of the water pipe being served?
  • How far are the air chambers from the equipment they serve?
  • What is the velocity of the incoming water?
  • What kind of equipment is being installed?

There is one last thing that can help in determining what kind of water hammer devices should be installed and their location. Make a sketch showing water piping as well as the locations of the fixtures and equipment.

Thanks you for reading and if you have any questions or you need clarifications please don’t hesitate to ask.

admin@theplumbinginfo

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