The best cure for banging water pipes is a water hammer arrester with a lubricated internal piston. The sealed piston works better than capped pipes, which eventually fill with water.
By the DIY experts of The Family Handyman Magazine:May 2000
Water hammering is caused by the quick shutoff
of water supply lines. The energy in flowing
water has to go somewhere, and when a valve is
shut off, the pipes can flex and “hammer”
against anything close—like nearby studs, joists
or other water pipes. Solenoid-triggered valves,
like the ones in dishwashers, washing machines
and water softeners, shut off almost instantly,
not only causing the most ferocious hammering
but also putting strain on rubber hoses and copper
sweat fittings. Hand-controlled faucets usually
don’t cause as much hammering because the
shutoff is more gradual.
The traditional solution of adding a capped length of copper pipe (A) works by trapping
a bubble of air that acts as a shock absorber for the back pressure, but it only works for a while. Eventually
the air bubble shrinks because the air gets
absorbed by the water until it disappears completely.
Instead, install a manufactured water-hammer
arrester (B and C), which is available at
home centers. It isolates the pocket of air from
the water in the pipes with a rubber-gasketed
piston. The closer you locate the arrester to solenoid
valves, the better. The model shown is
designed to mount between the spigot and washing
machine feed lines. If necessary, add more
in-line arresters in other water pipes near faucets
or valves to further reduce hammering.
The three most common types of water hammer arresters are:
A. Vertical, capped
C. Screw-in style
Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.
Avoid last-minute shopping trips by having all your materials ready ahead of time. Here's a list.
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