Question by oskeewow13: What could be the source of water hammer?

It seems that plumbing in my house has a problem with water hammer. First, I thought it only occurs when toilet tanks are filling back with water, but I realized that it happens whenever water is used anywhere in home. It just that water hammer is not as bad when I use faucets. So I've been trying to figure out where or source of this water hammer. By listening to where the sound is coming from, and by touching the water pipe with my finger tips, I learned that sound is loudest where the main water pipe comes in through the concrete wall. I guess I can install a water hammer arrestor. But I am trying to understand why water hammer is occuring. Here is my guess. Please let me know what you think. There is a branch near this point where pipe leads out to the faucet outside the house. While water tries to flow further into the house, perhaps vacumm is being creat ed in this branch pipe and causing water hammer. Is this possible? What do you think? Thanks!
1. Noise comes from pipes near water main, not the toilets. noise just louder with toilets, reduced intake valve and reduced noise
2. With my fingertips, I can feel the pipe vibrating.
3. Perhaps water traveling to water softner and bouncing back?
4. Checked diaphram valve on toilet, it looked fine.
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I guess I'll just install couple water arrestors and see what happens...




Best answer:

Answer by Michael N
Introduction-
What is Water Hammer? Water hammer is a pressure shock wave induced in plumbing supply systems whenever there is a sudden change in the steady state condition of a non-compressible liquid such as water. Pumps, valves, faucets, toilets, and fast solenoid-activated valves (such as commonly found in washing machines and dishwashers) are all examples of devices that can induce water hammer within a typical plumbing system. Water hammer can result in noisy, banging sounds as pipes rattle and expand to absorb the pressure wave. Shock waves in typical water pipes travel at up to 4500 feet/second and can exert tremendous instantaneous pressures, sometimes reaching 150 to over 1,000 PSI. If left unchecked, water hammer can damage pipes, valves and eventually weaken joints. However, the lack of noise does not mean that water hammer is not present.
Several factors exacerbate water hammer and are generally traceable to inadequate system design and installation. These include:

Improperly sized supply lines for given peak water flow velocity;
Excessive system water pressure and lack of pressure-reducing apparatus;
Inadequate strapping or securing o f plumbing to structure;
Excessively long straight runs with no bends;
Lack of expansion tank or other dampening system, such as water hammer arresters;
Newton's law states that for "every action there is an equal and opposite reaction." If water is flowing into a washing machine then is suddenly shut off, the kinetic energy of the flowing water reverses direction and must be dissipated during the transition to a steady state. This energy is initially reflected back through the plumbing system in a direction opposite to the original flow, creating an oscillating shock wave. Depending on the extent of the shock wave, a loud banging or rattling sound can be heard as pipes expand and move as the shock wave dissipates.

If there were no friction losses and if the pipes had no expansiveness, the shock wave would continue indefinitely. However, as water flows through the pipes, friction due to internal pipe surface irregularities helps to slow the water, res ulting in energy that is converted to heat. In addition, virtually all pipes -- including drawn copper tubing -- have some measure of elasticity. As the plumbing system encounters a sudden pressure shock wave, the pipes expand slightly to absorb the shock. Pressures in excess of several thousand PSI are possible during this brief instant, which is why water hammer can burst pipes and joints unexpectedly.

Failure to properly address water hammer can yield the following dangers, according to the Plumbing and Drainage Institute:

Ruptured piping
Leaking connections
Weakened connections
Pipe vibration and noise
Damaged valves
Damaged check valves
Damaged water meters
Damaged pressure regulators and gauges
Damaged recording apparatus
Loosened pipe hangers and supports
Ruptured tanks and water heaters
Premature failure of other devices
Clearly, repairing any of these conditions "after the fact" is more ex pensive and inconvenient than designing a system right from the start.




Traditional Solution to Water Hammer Traditionally, the solution to water hammer has been to install pipe risers inside the wall at each faucet or valve junction. Sometimes these risers would be as high as 24" or more, depending on the pipe diameter. In theory, the risers would trap air as the plumbing system is first activated. The column of air acts as a natural damper, compressing as it absorbs residual shock waves from a sudden change in the supply flow.
Many, if not most older homes today have such systems and some plumbers continue to install air risers because "that's the way they've always done it." However, what is not readily understood is that these risers eventually fail due to water logging. Over time, the trapped air in the risers dissolves into the water supply itself and the water level gradually rises until the air chamber is completely void of air at all. For this reason, some people who have never experienced the sound of water hammer may suddenly start complaining of "strange noises inside the walls."

The only real solution is to completely drain the home's water supply system at the lowest point and gradually re-pressurize it. However, this solution is temporary at best, since the air chambers will eventually become waterlogged once again, thereby eliminating their effectiveness.

What's more, further studies have also found possible health problems associated with air risers, such as an accumulation of rancid water, bacteria, minerals, and other muck that festers in the dark, dead-end chambers. If left unchecked and untreated, this could eventually contaminate the entire household water supply causing unexplained illness.

Therefore, modern practice and, indeed, many plumbing codes , now prohibit air chambers in new construction. In any case, if you are remodeling or building a new home, DO NOT use air chambers to mitigate water hammer problems. Rather, design the system right from the start and you'll never have to worry about it again. A combination of proper pipe sizing and water hammer arresters are all that's necessary in most situations.

Prevention by Design If air chambers, then, are not an approved method of dampening the impact of water hammer, what is the correct method? First, let's consider new construction where there is no existing legacy plumbing.
In the case of a new home, there is total flexibility in sizing the water supply lines properly. Empirical studies conclude that water hammer is greatly mitigated when water velocity is kept below 5 feet/second within the pipe. This is a conservative number. And while CPVC plumbing is increasingly common (and is somewhat more for giving at higher velocities due to its increased expansiveness), copper plumbing is still the mainstay of most commercial and residential plumbing systems today and is the focus of this technical note.

To assist contractors and plumbers in sizing the water supply line diameter at each branch of a plumbing supply system, Builders Websource has constructed several tables comparing Type K, L and M copper tubing. While type K is rarely used in residential construction, type L and M are more typical. Type K copper, denoted by its green labeling, has the thickest wall of all three types, whereas type M (denoted by red labeling) is the thinnest. Since the outer diameter for all three types is fixed, type M actually provides slightly greater internal cross section for a given pipe size due to its thinner wall size. While this can help to reduce water hammer by a small fraction, the thinner wall size is more susceptible to bursting and pin hole leaks over time. Type L copper is the best compromise for price/value and is a proven all-around performer for commercial and residential use above ground.

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