I have a 2-year old house. In order to install several new hose bibbs, I
recently shut off the main water supply at the gate valve where the pipe
enters the house. After restoring the water supply, I noticed water hammer
at every faucet, dishwasher, and washing machine in the house. I never had
a problem with water hammer before.
I measured water pressure to the house at 55 psi. There is a Zurn (Wilkins)
thermal expansion tank Model WXTP-8 (2.1 gallon) above my water heater, and
the pressure at the air valve on the tank measures 55 psi. There is no
separate water hammer arrestors anywhere in the system.
How can I restore the quiet operation that I had before replacing the hose
bibbs? Is there a certain way to drain the system that will solve the
problem? Do I need to discharge and recharge the expansion tank? Or what??
Somehow, when you drained the system you lost the air head in the anti
hammer devices, probably located near the washer. You will need to
turn off the water and maybe drain fromt the boiler drains at the
washing machine to regain the head. good luck, RW
Key Bored wrote:
I might suspect the gate valve itself. Make sure it's all the way open.
The fact you shut the water off and turned it on again shouldn't have
affected the air chambers (if you had any to begin with). As a matter of
fact, air chambers that are not accessible, don't do any good after a while.
Eventually, the air in the chambers gets mixed into the water supply making
them waterlogged anyway.
The way you wrote your message, since it happens at every faucet, and
since it happens on the hot and cold, I'd think the problem would have to be
where the source of the water for all those fixtures are, and the gate valve
is a likely suspect. A loose gate can rattle.
......Or even more likely.....
The poster is simply calling "water hammer" what we all know as simply
having air in the lines after a shut down. He may simply need to purge the
Thanks to all for suggestions. While checking all valves in the water
supply system, I noticed the sensor valves under the sinks in the bathrooms.
These valves are part of the hot water recirculation system, along with a
small electric pump above the water heater. The sensor valves open and
close automatically depending on the water temperature, so that hot water
(actually warm water) is available at the sink at all times. When the
sensor valves were in the closed position, it caused the water hammer. The
retrofit recirculating system is sold at Home Depot, and is described at:
When I removed the sensor valves, the water hammer stopped. I was never
happy with the recirculating system in the first place, because it used the
cold water supply line as a return line to the water heater, and as a
result, the cold water at the sink was warm until I ran the faucet for about
30 seconds. In other words, I traded one problem (waiting for hot water)
for two others (water hammer and waiting for cold water). I wouldn't
recommend this system to anyone.
Are you sure you mean "water hammer" (a single bang when a valve is closed
quickly) or "cavitation" a series of rythmic banging that happens when a
valve flutters (or other causes) due to malfunction for example. Like a
machine gun in the pipes. In any case, it sounds like you solved the
problem well enough for yourself.
I want to put a recirc system in but one activated by a button not
continuously primed. They do save water but at the expense of more pricy
gas or electricity as even insulated pipes will loose some heat.
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