Water Hammer Arresters
by Sioux Chief
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Please note: Unless specifically noted, items on this page are not for potable/drinking water.
Water hammer is usually recognized by a banging or thumping in water lines. The noise can occur when the flow of moving water is instantaneously stopped by a closing valve, or there are loose pipes in the wall, or there is a worn out washer on a faucet. The sudden stop of water, or a stutter caused by a loose or bad washer, results in a pressure spike behind the valve which acts like a tiny explosion inside the pipe. This pressure spike will create shock waves in the water that will reverberate throughout the plumbing system, rattling and shaking pipes, especially loose pipes, until it is absorbed.
Normally, a sufficient pocket of air will absorb such a pressure spike, but if no pocket of air is present, expensive fixtures and appliances within the plumbing system will be damaged as they are left to absorb this pressure spike.
Arrester Sizing Table
Use this table to determine how many fixture units you have. Choose the arrester with the corresponding fixture unit rating. C.W. means cold water line, H.W. means hot water line
| Fixture |
Type of
Supply Control |
Fixture Units |
| Public |
Private |
| Total |
C.W. |
H.W. |
Total |
C.W. |
H.W. |
| Water Closet 1.6 gpf |
Flush Valve |
8 |
8 |
-- |
5 |
5 |
-- |
| Water Closet 1.6 gpf |
Flush Tank |
5 |
5 |
-- |
2.5 |
2.5 |
-- |
| Pedestal Urinal |
Flush Valve |
4 |
4 |
-- |
-- |
-- |
-- |
| Stall or Wall Urinal |
Flush Valve |
4 |
4 |
-- |
-- |
-- |
-- |
| Stall or Wall Urinal |
Flush Tank |
2 |
2 |
-- |
-- |
-- |
-- |
| Lavatory |
Faucet |
2 |
1-1/2 |
1-1/2 |
1 |
1 |
1 |
| Bathtub |
Faucet |
4 |
2 |
3 |
2 |
1-1/2 |
1-1/2 |
| Shower Head |
Mixing Valve |
4 |
2 |
3 |
2 |
1 |
2 |
| Bathroom Group |
Flush Valve Closet |
-- |
-- |
-- |
8 |
8 |
3 |
| Bathroom Group |
Flush Tank Closet |
-- |
-- |
-- |
6 |
6 |
3 |
| Separate Shower |
Mixing Valve |
-- |
-- |
-- |
2 |
1 |
2 |
| Service Sink |
Faucet |
3 |
3 |
3 |
-- |
-- |
-- |
| Laundry Tubs (1-3) |
Faucet |
-- |
-- |
-- |
3 |
3 |
3 |
| Combination Fixture |
Faucet |
-- |
-- |
-- |
3 |
3 |
3 |
| Clothes Washer |
Solenoid Valve |
-- |
-- |
-- |
4 |
3 |
3 |
| Dishwasher |
Solenoid Valve |
-- |
-- |
-- |
1.5 |
-- |
1.5 |
| Ice Maker |
Solenoid Valve |
-- |
-- |
-- |
1 |
1 |
-- |
RULE 1: Branch Lines of 20 Feet or Less
The Hydra-Rester should be placed at the end of the branch line between the last two fixtures served as shown below.
RULE 2: Branch Lines Over 20 Feet
An additional Hydra-Rester (Y) should be placed as shown (below). The additional unit should be placed at the midpoint of the run longer than 20 feet. The sum of the fixture unit ratings of units X and Y combined, should be equal to or greater than the demand of all branches.
Hydra-Rester - Multi-fixture Water Hammer Arresters
Male Pipe Thread Models (MIP)
Male "Sweat" (Solder) Models
All sweat models are compliant with the 2014 Federal Safe Drinking Water Act
Mini-Rester
Single Fixture Water Hammer Arresters
Laundry Mini-Rester #660-H
- 2014 Federal Safe Drinking Water Act compliant - suitable for use with potable/drinking water.
Comments/suggestions from one of our water hammer arrestor customers:
I always use male threaded and not solder type, because in hard water areas they will, with time, seize and need to be replaced. Much easier to turn off the water and unscrew a device than do all that soldering. Because they can seize I always avoid putting them inside walls.
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Related Items & Information
Frequently Asked Questions
Q. "What is water hammer?"
A. Water hammer occurs a lot! It is frequently recognized by a "thump" or "bang", usually throughout the water line (if you have copper pipes, you'll tend to hear the noise throughout the house). Water hammer can be caused by a number of things. Many times a loose washer that is jumping around in the faucet or valve causes it. This can be fixed by identifying which valve is the culprit and fixing the washer. Other times it is simply caused by water traveling at a rapid rate and suddenly being shut off. The best solution for this is to increase the size of the water supply thereby slowing down the water (a larger pipe being able to deliver the same amount of water in gallons per minute at a slower speed). If this is not possible, then many times a water hammer arrester helps. Sometimes the cause is excessive pressure and the best way to deal with that is to install a pressure regulator as well as an expansion tank (needed by many codes once you install a pressure regulator). In any case, please be aware that sometimes water hammer arresters will not solve your water hammer problem.
Q. "What are your most popular hammer arresters?"
A. The 1/2" through 1" (models 652-GA, 653B and 654C with standard male threads) for most situations, as well as the 660-H which is specifically for hose threads on appliances such as clothes washing machines.
Q. "Can these water hammer arrestors be installed inside a wall?"
A. Yes. All of the water hammer arrestors shown above are approved for sealed wall installations with no access panel required.
Q. "Will water hammer arrestors stop all banging inside my wall? Will it solve my noisy pipes problems?"
A. The water hammer arrestors will not compensate for poor strapping practices. If they are needed and work it is because faucets or valves can be closed too rapidly and create a water hammer. In other words, water hammer arrestors can solve some problems but not all. If you have both bad brakes and bald tires on a car then getting new tires won't solve all of your problems. Same with water hammer arrestors. They can't solve expansion and contraction issues or poor strapping issues but they certainly can usually help somewhat with water hammer issues.
Q. "I see that you have soldered (male sweat) models of water hammer arresters. They seem like a great idea since I won't have to use copper fittings?"
A. Yes, they are a great idea IF you are REALLY good at soldering (not overheating). We offer them because we get asked for them. We would like to warn you to not overheat them while soldering as you could then damage the seals. For copper installations, we like to recommend the male threaded type of water arresters (or the compression type if you are using hard copper pipe).
Q. "At what angle can these water hammer arrestors be installed?"
A. Because of their secure water chambers, all Hydra-Restors and Mini-Restors can be installed at any angle.
Q. "We have a high efficiency front loading washing machine. We installed a 660-H on the hot and cold supply lines yet we still have some water hammer noise. How come?"
A. According to the manufacturer one pair of water hammer arresters (Mini-Resters) placed within six feet of the valve should be sufficient to control a pressure rise up to 150 psig maximum and reduce noise caused by uncontrolled water hammer. This should be no different for high efficiency front loading washing machines or common residential washing machines. Most high efficiency front loading washing machines use less water per wash cycle than conventional washing machines. However, their water supply valves turn on and off as many as 16 times per cycle as compared to 3 or 4 times a cycle for conventional machines. This higher supply valve usage may cause a low level, repetitive noise annoying enough to cause the homeowner to assume the Mini-Resters are not working. The pressure surge may be sufficiently controlled by the Mini-Resters and be working as designed yet not eliminate the noise completely. In an effort to further reduce or eliminate this noise, the manufacturer suggests an additional set of Mini-Resters be installed on the supply lines. This means two Mini-Resters installed on each supply hose. With 2 arresters on the cold line and 2 on the hot line, the pressure surge can be further reduced.
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Customer Testimonials
"Thank you very much for fulfilling my order. Your web site's descriptions and pictures made ordering my water hammer arrestors a breeze. After installing the arrestors on my toilets, washing machine hook-ups, and ice-maker line, my plumbing is now silent. I cannot believe I have gone this long listening to banging pipes. Thanks again."
- Stephen Horvath, Wellington, FL 33414
Please note that every customer testimonial shown on our pages has given us written permission to quote them. Our customer's privacy is very important to us, and we will never give, share or sell contact information or e-mail addresses to anyone!
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