If you’ve ever heard pipes bang or thud when a faucet snaps shut or a washing machine stops filling, that’s likely water hammer—a shockwave that travels through your plumbing when fast-closing valves suddenly stop moving water. In copper-piped Colorado homes (very common across the Front Range), those pressure spikes can stress soldered joints, valves, and the mostly plastic internals of many appliances.
Quick refresher: what causes water hammer?
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Sudden valve closure (ice maker, dishwasher, laundry valves, irrigation zone valves) stops moving water, sending a pressure wave through the piping.
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Check valve slamming or pump starts/stops can add to the effect on well/booster systems.
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Entrapped air and poor air relief can worsen shocks.
Per the International Plumbing Code (IPC §604.9), a water-hammer arrestor is required wherever quick-closing valves are used. That includes modern appliances and many fixture shutoffs.
How arrestors (and expansion tanks) help
A water hammer arrestor is a small device that sits near the quick-closing valve and acts like a shock absorber, converting the momentum surge into a cushioned stop. An expansion tank handles thermal expansion from your water heater, which helps keep overall pressures stable between appliance cycles. (Think of the arrestor as the sprinter’s shock shoe, and the expansion tank as the track that’s not rock-hard.)
Colorado context: pressure matters
Along the Front Range, household pressures commonly land in the 50–70 psi range, but many neighborhoods sit higher—some districts average ~75 psi, and anything over ~70–80 psi can accelerate wear on fixtures and appliances. A properly set pressure-reducing valve (PRV) (often around ~60 psi) plus arrestors near quick-closing valves is a great one-two combo.
Where to install arrestors (typical homes)
Best practice—and what the sizing standards show—is as close as practical to the quick-closing valve or at the end of the branch between the last two fixtures on that run. Priorities:
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Washing machine (both hot and cold)
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Dishwasher
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Refrigerator ice maker
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Irrigation/sprinkler zones
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Long fixture branches serving multiple quick-close points
These locations align with PDI WH-201 and manufacturer guides for sizing and placement.
Sizing 101 (keep it brief, get it right)
Pros size arrestors by pipe size, branch length, flowing pressure, and connected fixture units. The industry uses PDI WH-201 letter sizes (A–F); for example, a long ¾" branch may call for two “C” units or a larger single unit depending on the run and load. If you’re unsure, have us size it from the charted method.
Materials & lifespan: copper vs. stainless
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Standard piston/bladder-type arrestors are common and economical, but their internal gas charge or moving parts can wear out over time—especially with higher pressures or hard water. You’ll often know it’s time when the banging returns.
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Stainless bellows-type arrestors (e.g., Zurn Shoktrol Z1700, Watts SS-Series, MIFAB bellows models) replace rubber membranes with a stainless bellows, marketed as maintenance-free with long service life and excellent shock capacity. These models are PDI WH-201 certified / ASSE 1010 listed when specified, and are a great “install it once, forget it” upgrade—especially on laundry and irrigation lines that hammer hard.
Tip: If your home regularly sees pressures above ~70 psi, consider PRV adjustment or replacement first, then add arrestors where needed. This reduces both chronic and acute stress.
Do arrestors need maintenance?
They’re passive—but they can lose effectiveness over time. Piston or bladder types may become waterlogged; stainless bellows types are designed to avoid that failure mode. During annual plumbing checkups, we:
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Verify your static pressure (target ~60 psi unless a special need).
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Inspect accessible arrestors for leaks/corrosion and retest hammer events (laundry fill start/stop, dishwasher, irrigation).
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Check expansion tank charge and PRV performance.
Red flags you shouldn’t ignore
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Banging/knocking that comes back after a quiet period
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New hammer noises after adding an appliance or irrigation zone
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Visibly vibrating copper when valves close
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Leaks at appliance valves, braided connectors, or stops
Our recommended approach for Colorado homes
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Pressure audit (hose-bib gauge, hot/cold, multiple times of day). If >70–80 psi, adjust/replace PRV.
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Targeted arrestors: AA-size (or per chart) at laundry, dishwasher, ice maker, and zone valves—placed close to the valve.
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Expansion tank check for water heater (helps tame overall system spikes).
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Stainless bellows upgrade on high-hammer branches for a longer service life.
FAQ
Is an expansion tank the same as a water hammer arrestor?
No. An expansion tank handles thermal expansion (slow pressure rise), while a water hammer arrestor handles instant pressure spikes from quick-closing valves. Both help protect your plumbing.
Will an arrestor fix every noise?
Not always. We also look for loose pipe supports, over-tightened quick-close valves, check valve slam, and air issues.
Are arrestors required by code?
Yes—IPC §604.9 requires arrestors where quick-closing valves are used. Many Colorado jurisdictions are on an IPC basis with local amendments.
Call Oasis Plumbing Co.
If your pipes are banging—or you’re replacing a dishwasher, washer, or irrigation system—we’ll size and place arrestors to code and tune your PRV so everything runs quietly and safely.