Did you ever turn off a faucet only to experience sounds and vibrations similar to those produced by a three-point earthquake? Here's why: Imagine a fast-moving stream of water traveling down a narrow pipe. Suddenly and unexpectedly the water finds a closed valve in place of what moments earlier was an escape point.
All of a sudden the water has nowhere to go. Whether the water source is a well, a local storage tank or a community system, one fact is constant water doesn't compress. As it comes to an abrupt stop a loud thud results that, more often than not, can be heard throughout the house. The noise is known as a "water hammer." The hammering action that creates the racket is capable of damaging joints and connections in the pipe.
So, why doesn't your plumbing system make a loud noise every time a fixture is turned off? First of all, not every water valve closes quickly. In fact, most valves close slowly enough to prevent water hammer. As gaskets in a faucet get old and brittle, however, they can cause the faucet to close more quickly, and a water hammer can result.
Air chambers are added to the plumbing system when it is first installed to act as cushions to prevent water from slamming against the piping. Since air compresses, it absorbs the shock of the fast-moving water before it has a chance to slam against the end of the pipe. Many household plumbing systems have air chambers built into them at critical locations such as the clothes washer or dishwasher where electric shut-off valves close rapidly. In some homes air chambers are located at every location where water is turned on and off even the toilet. Most of the time you can't see air chambers because they are hidden within the wall with the rest of the pipes.
An air chamber is a vertical pipe located in the wall cavity at the point near a faucet or valve where the water supply pipe exits the wall. The pipe that makes up the actual air chamber usually terminates about 12 inches above the point where the supply pipe exits the wall. Although they remain concealed in the wall, air chambers are close enough to the fixture to properly cushion the water. The air chamber acts as if it were an upside-down water glass. Once filled with air it becomes a perfect cushion. In copper systems, a one-piece pipe called a closed nipple is used to make air chambers, and since they are one piece there is no place for the air leak thus, these are the most dependable kind.
In older systems that use threaded pipe, the air chamber is made from a capped nipple. Here there is the chance that air can leak from the cap allowing the air chamber to fill with water rendering it useless and making a once quiet, functional water supply system noisy and prone to damage.
The most common way to eliminate a water hammer is to replenish all air chambers with air. You can't inspect the air chambers, so this procedure is a must. Here's how: First, shut off your home's main water supply valve. Next, open a few faucets inside your house. Then, find the faucet on the property that is located at a lower elevation than all the rest usually outside. Turn it on to drain all water from the pipes. Some folks incorrectly refer to this as "bleeding" the system. Normally, when you bleed a system it is in an attempt to remove air. In this case we want to add air. As the water is drained from the pipes, it automatically is replaced by air this includes the air chambers. The moment the water is completely drained from the piping the lowest faucet should be turned off and the main valve reopened. Air will be pushed out of the horizontal and open vertical water lines and will sputter as it exits the faucets inside. However, air will remain in the upside-down air chambers, and, in most instances, this procedure will eliminate a water hammer.
Sometimes a water hammer can occur when there is a loose pipe-mounting strap. A loose pipe strap can allow the pipe to move freely and vibrate against framing members as water is turned on and off. This can happen even if all the air chambers are in good shape. So, be sure to check all accessible pipes to ensure that they are properly and tightly connected.
By the way, there is another kind of air chamber called a shock absorber. A shock absorber is fitted with a gas-filled bladder that is connected to a piston. They say the bladder won't leak and is supposed to last forever. It is our opinion that the fewer mechanical devices you have in your plumbing system, the better. A simple conventional air chamber can be refilled with air in a few minutes so, who needs pistons?
