How To Install Water Hammer Arrestor: A Step-by-Step Plumbing Guide
A water hammer arrestor is a specialized hydraulic cushion device installed near fast-closing valves to absorb destructive pressure shockwaves and protect residential plumbing infrastructure. Proper sizing and placement on hot and cold supply lines near washing machines, dishwashers, and quick-acting faucets ensure long-term pipe stability and prevent joint leaks.
Pre-Operation & Equipment Checklist
Successful installation of a water hammer arrestor requires a systematic approach to plumbing safety, correct sizing, and precise tool selection. Before cutting into supply lines, verify that all necessary components and safety gear are staged to minimize water shutoff time and prevent structural water damage.
- Essential gear, tools, and materials: Tubing cutter, adjustable wrenches, plumber's tape (PTFE), emery cloth or wire brush, flux, propane torch and solder (if working with copper), or appropriate PEX crimping tools and fittings, a clean bucket, rags, safety glasses, and appropriately sized water hammer arrestors (typically PDI-certified Type AA, A, B, C, D, or E depending on fixture units).
- Mandatory prerequisite knowledge and standards: Compliance with local plumbing codes (such as the International Plumbing Code or Uniform Plumbing Code), understanding of shutoff valve locations, and adherence to manufacturer pressure ratings, which generally handle up to 250 psi working pressure and 350 psi burst pressure.
- Estimated budget and duration benchmarks: Financial cost typically ranges from fifteen to fifty dollars per arrestor depending on body material (brass vs. stainless steel), with total installation time estimated between thirty and sixty minutes per fixture location.
Execution Workflow for Water Hammer Arrestor Installation
Step 1: Locate the Main Water Supply and Drain the System
Locate the main house water shutoff valve and turn it completely clockwise to stop incoming pressure. Open the highest and lowest faucets in the building to relieve residual pressure and drain standing water from the vertical and horizontal risers. Place a bucket and rags underneath the intended installation zone to catch any trapped moisture before cutting into the pipe.
Warning: Always verify that water pressure is fully dissipated by opening downstream taps before cutting into any copper or PEX supply lines to prevent accidental flooding or scalding.
Step 2: Identify the Optimal Placement Point
Determine the exact location for the water hammer arrestor by inspecting the supply lines feeding the offending appliance, typically a washing machine box or refrigerator supply line. According to Plumbing and Drainage Institute (PDI) standard WH-201, the arrestor should be installed as close as possible to the source of the shockwave, ideally on the vertical riser immediately preceding the quick-closing valve, pointing upward or horizontally.
Step 3: Prepare the Pipe Surfaces
Clean the exterior of the supply pipe thoroughly using emery cloth or a fitting brush until the metal shines bright silver, removing all oxidation, grease, and debris. If working with PEX piping, cut the line cleanly and squarely with a specialized PEX tubing cutter, ensuring no burrs or jagged edges remain on the interior or exterior circumference.
Step 4: Install the Tee Fitting and Arrestor Assembly
Integrate a threaded tee fitting into the water supply line by soldering the copper joints or crimping the PEX connections securely into place. Wrap male pipe threads with three to four wraps of PTFE plumber's tape in a clockwise direction, then thread the water hammer arrestor into the threaded branch of the tee fitting. Tighten the arrestor firmly with an adjustable wrench, ensuring a watertight seal without over-tightening, which can strip threads or distort internal O-rings.
Pro-Tip: If you are installing a threaded arrestor onto a copper stub-out, use a backup wrench on the tee fitting to prevent torquing and twisting the supply line during final tightening.
Step 5: Pressurize and Test the Plumbing System
Close all open faucets and slowly open the main water supply valve to re-pressurize the household plumbing system at a gradual rate to prevent destructive water hammer spikes during initial filling. Inspect all newly installed soldered or crimped joints and threaded connections for signs of weeping or active leaks. Operate the washing machine or quick-closing valve through a test cycle to confirm that the banging noise is completely eliminated.
Where Do I Install A Water Hammer Arrestor at Susan Taube blog
Water Hammer Arrestor Selection and Sizing Matrix
| PDI Size Designation | Fixture Unit Range | Typical Residential Application | Body Material Options |
|---|---|---|---|
| Type AA | 1 to 2 Fixture Units | Single-handle faucets, ice makers | Brass, Copper |
| Type A | 3 to 4 Fixture Units | Dishwashers, standard washing machines | Brass, Stainless Steel |
| Type B | 5 to 11 Fixture Units | Multi-fixture bathroom groups | Brass, Bronze |
| Type C | 12 to 32 Fixture Units | Commercial laundry equipment | Stainless Steel |
Troubleshooting Common Installation and Operational Failures
- Persistent Banging After Installation: Root cause is typically incorrect placement too far downstream from the quick-closing valve or an undersized arrestor capacity. Actionable fix is to relocate the arrestor closer to the source valve or upgrade to a higher PDI fixture unit rating.
- Leaking Threaded Connections: Root cause includes insufficient PTFE tape, crossed threads, or under-tightening against the internal sealing gasket. Actionable fix is to unthread the arrestor, inspect the threads for damage, apply fresh tape, and retighten to manufacturer torque specifications.
- Premature Arrestor Failure: Root cause stems from a ruptured internal piston seal caused by extreme system pressure spikes exceeding 150 psi or water hammer accompanied by thermal expansion. Actionable fix is to install a pressure-reducing valve (PRV) on the main line alongside a thermal expansion tank.
Frequently Asked Questions
Can water hammer arrestors be installed horizontally?
Yes, most modern piston-type and bellows-type water hammer arrestors can be installed in vertical, horizontal, or angled orientations without compromising their shock-absorbing efficiency. Always verify the specific manufacturer documentation to ensure the internal piston travels freely in your chosen mounting plane.
How long do water hammer arrestors typically last?
A quality arrestor constructed from brass or stainless steel will generally last between ten and twenty years depending on water chemistry, mineral content, and system pressure fluctuations. Sealed piston units may eventually experience internal O-ring wear, leading to water logging where the air chamber fills with water and loses its cushioning effect.
Do I need an arrestor on both hot and cold supply lines?
Yes, you should install a water hammer arrestor on both the hot and cold water supply lines wherever a quick-closing valve exists. Both lines experience identical hydraulic shock dynamics when solenoid valves snap shut during washing machine fill cycles.
Can I install a water hammer arrestor myself without a plumber?
Homeowners with basic DIY plumbing experience and appropriate tools can easily install thread-on arrestors onto washing machine shutoff valves or compression tee fittings. Soldering copper pipes requires open flame proficiency, whereas PEX systems require specialized crimp rings and calibration tools.
What causes water hammer in residential pipes?
Water hammer occurs when a fast-moving column of water is suddenly stopped by a closing valve, creating a high-pressure shockwave that travels backward through the plumbing. This hydraulic shock causes pipes to bang against framing members, potentially weakening joints and bursting fittings over time.
Protect your home plumbing system from destructive hydraulic shock by upgrading to professional-grade water hammer arrestors today. Browse our selection of certified plumbing hardware to find the exact configuration for your project requirements.
