Water hammer?

[billrector]

Back in our 2017 FC on our way to the Keys. First use since winterizing. We have hot and cold water and the pump seems to be working fine. However, when we run the faucets or flush the toilet, there is a few second (3-4) long vibration on the opposite side of the trailer from the pump. We have used 20+ gallons of water so that should have gotten any air out of the system and there is no sputtering. I have also run water through the water heater pressure valve, but none of this fixes the noise. Ideas?

[azflycaster]

Hammering is due to air pockets. Have you run water through every valve in the trailer? Outside shower, if you have one, is often overlooked...

[Adventure.AS]

Originally Posted by billrector

Back in our 2017 FC on our way to the Keys. First use since winterizing. We have hot and cold water and the pump seems to be working fine. However, when we run the faucets or flush the toilet, there is a few second (3-4) long vibration on the opposite side of the trailer from the pump. We have used 20+ gallons of water so that should have gotten any air out of the system and there is no sputtering. I have also run water through the water heater pressure valve, but none of this fixes the noise. Ideas?

This trick was shown to me by Andy Thompson at Can-Am RV.

The hot water tank works like an accumulator in the system. If the air gap is missing at the top of the tank you will get the water hammer when using the pump. Try letting some water out of the tank by toggling the pressure relief valve to let some hot water out of the tank.

[GCinSC2]

Originally Posted by Adventure.AS

This trick was shown to me by Andy Thompson at Can-Am RV.



The hot water tank works like an accumulator in the system. If the air gap is missing at the top of the tank you will get the water hammer when using the pump. Try letting some water out of the tank by toggling the pressure relief valve to let some hot water out of the tank.

The T&P relief valve is below the top of the tank right? Wouldn’t the procedure to reestablish the air pocket be to turn water off, turn HWT off, drain HWT completely careful it’s hot water, leave T&P closed, replace drain plug in tank and fill system leaving T&P closed.

[lsbrodsky]

Yes! The procedure for doing this is even in my 2012 manual, as a cure for a relief valve that is spitting. Have done this for a number of club members over the years. You can lose the air bubble over time, even before the season is over.
Larry

[link2dks]

From my Dometic GE9EXT water heater manual in a 2019 Globetrotter:


"TO REPLACE THE AIR GAP FOLLOW THESE STEPS:
1. Turn off main water supply (the pump or water hook up source). 2. Let water cool or let run until cool.
3. Open the hot water faucet closest to the water heater.
4. Pull handle of pressure temperature relief valve straight out and
allow water to flow until it stops.
5. Allow pressure temperature relief valve to snap shut; close faucet;
turn on water supply.
6. Turn on water heater and test."

Easy to do, don't forget to let the water in tank cool first. The manual also states that the air gap will go away over time (they don't say how long) because the air will gradually be absorbed by the "expanding water".

Dave S

[GCinSC2]

Dave S,

Sounds a bit easier than my armchair comment, again RTFM.

Gary

[link2dks]

GCinSC2

LMAO, In had to look that one up.

Dave S

[GCinSC2]

Originally Posted by link2dks

GCinSC2



LMAO, In had to look that one up.



Dave S

Works about 90% of the time the other 10% is blowing in the wind.

Greetings from lower Carolina to upper but in the traffic shadow of CLT Carolina.

Gary

[Landshark]

This thread really made me feel my age: don't understand a single one of these acronyms (textonyms)?.

[GCinSC2]

Cerb,

I might be similar age bracket. I remember where I was when JFK was assassinated.

RTFM could be a standard reply for a bunch of queries here.

Read The Friendly Manual

And CLT is Charlotte NC and the area that Dave lives in can have some pretty horrific traffic I-77 has been in near constant construction for long time and driving an Airstream on it will get your attention.

My mom was fluent in shorthand. Not me.

Pocatello traffic is taters and beet wagons or am I off by a bunch of counties.

Don’t forget to use the dipstick and check the height of your water to air interface. JK just kidding.

Gary

[rmkrum]

Sigh. I was a junior in high school when we heard JFK got killed.

Boy, that was a hugely long time ago...

“I used to be young and foolish, now I’m no longer young..”

[BayouBiker]

Originally Posted by azflycaster

Hammering is due to air pockets. Have you run water through every valve in the trailer? Outside shower, if you have one, is often overlooked...

Just to be clear so no reader is confused, water hammer occurs in the ABSENCE of air pockets. They are due to shock waves initiated by inertial forces of incompressible fluids when a valve is closed quickly.

Air is compressible and thus when there is sufficient air somewhere in the direct path of the shock wave, the wave will immediately dissipate before it hits a hard stop on the far end of the pipe run and cause the hammer effect. Without air the wave will ring back and forth slowly dissipating.

The fix for water hammer has been described by others which is to get a bit of air into the top of the water heater, as it is the only space in these Airstreams designed to "accumulate air".