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Old 07-25-2013, 12:55 PM   #1
geo
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Black Tank Flush Vacuum Breaker - "Water Hammer Warning"!

I have no idea why this subject didn't occur to me earlier or why I am just now getting around to posting it! Apologies!

I would certainly hate to try to count the "problems with the black tank flush vacuum breaker" posts on the Forum! However, a friend with a similar fiver to mine mentioned one of the major causes for leaking vacuum breakers. Probably even more common that not winterizing them!

Water hammer!

The purpose of the vacuum breaker to to assure there is not siphoning from the black tank, and also to provide a means for each elevated pipe "leg" of the system to be drained. Thus when one connects a hose to the supply side of the black tank flush system, then walks over and turns the water on full blast, a solid core of water rushes through the piping and rams into the plastic parts of the vacuum breaker! Kinda like hitting your thumb with a claw hammer! His warning to me was the water only needs to be turned on to just a slow stream to fill the pipes through the vacuum breaker, and then turn it on full stream.

Makes sense when one thinks of all the flooded basements, underbellies, etc., that members have complained about for years.

Here's a diagram of what the system looks like:
http://www.keystonerv.org/forums/sho...ighlight=flush

And for those who are thinking about replacing their vacuum breaker: http://www.keystonerv.org/forums/sho...ighlight=flush If you do this replacement, be sure to get a valve rated for Water/Oil/Gas and install it correctly.

Ron
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Old 07-25-2013, 01:12 PM   #2
Festus2
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Quote:
Originally Posted by geo View Post
I have no idea why this subject didn't occur to me earlier or why I am just now getting around to posting it! Apologies!

I would certainly hate to try to count the "problems with the black tank flush vacuum breaker" posts on the Forum! However, a friend with a similar fiver to mine mentioned one of the major causes for leaking vacuum breakers. Probably even more common that not winterizing them!

Water hammer!

Ron
Ron -
Thanks for this timely post. Have no fear of being assessed a fine for handing in your assignment "late". And we've all lost track of the number of black tank flush threads and posts.

Makes a lot of sense - even to me.
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Old 07-26-2013, 10:06 AM   #3
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I dont have a leaking vacuum breaker yet but just yesterday I emptied my black tank and went to use the black tank flush and nothing happened. Come to find out there is pressure building up in the line and no water is getting to the tank. Any suggestions on what could be wrong? It used to work the last trip just fine and now nothing.
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Old 07-26-2013, 02:18 PM   #4
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Originally Posted by TandE View Post
I dont have a leaking vacuum breaker yet but just yesterday I emptied my black tank and went to use the black tank flush and nothing happened. Come to find out there is pressure building up in the line and no water is getting to the tank. Any suggestions on what could be wrong? It used to work the last trip just fine and now nothing.
TandE -
Hmm, first I think I would check the filter screen on the inlet. If OK, then check the Pex lines for any kinks. If OK, while the Pex lines are exposed, have someone connect a hose and start the water while observing the Pex lines. If you have around 40# pressure, then the Pex should fill to around 7/8 of the hose to the blockage. So, if it fills to almost the vacuum breaker but not past, the vacuum breaker is the problem and needs to be replaced. However, if it fills past the vacuum breaker and almost to the black tank, then it is a plugged black tank sprayer.

Any other thoughts out there?

Ron
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Old 07-26-2013, 03:06 PM   #5
hankaye
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geo, Howdy;

When I turn on the water for the flush system it's a slow easy process,
about 1/2 turn at a time. Makes for a peaceful event.
When I replaced my vacuum breaker with the plane-jane sharkbite elbow
I also bought a brass screw on vacuum breaker that I screw onto the spigot
and attach the hose to it. Bare in mind that my inlet to the trailer is about
2 feet above my tank. That allows gravity to work in both directions for me.
Has worked fine for over 2 years of continuous use. Dump once a week,
wither it needs it or not

hankaye
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Old 07-29-2013, 02:39 AM   #6
TandE
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Quote:
Originally Posted by geo View Post
TandE -
Hmm, first I think I would check the filter screen on the inlet. If OK, then check the Pex lines for any kinks. If OK, while the Pex lines are exposed, have someone connect a hose and start the water while observing the Pex lines. If you have around 40# pressure, then the Pex should fill to around 7/8 of the hose to the blockage. So, if it fills to almost the vacuum breaker but not past, the vacuum breaker is the problem and needs to be replaced. However, if it fills past the vacuum breaker and almost to the black tank, then it is a plugged black tank sprayer.

Any other thoughts out there?

Ron
Thanks for the reply. The inlet screen was my first suspicion but all is clear. From what I saw no water was getting past the breaker so it might be that. Will have to do a couple tests or maybe just call the dealer and schedule an appointment since it is still under warranty.




Quote:
Originally Posted by hankaye View Post
geo, Howdy;

When I turn on the water for the flush system it's a slow easy process,
about 1/2 turn at a time. Makes for a peaceful event.
When I replaced my vacuum breaker with the plane-jane sharkbite elbow
I also bought a brass screw on vacuum breaker that I screw onto the spigot
and attach the hose to it. Bare in mind that my inlet to the trailer is about
2 feet above my tank. That allows gravity to work in both directions for me.
Has worked fine for over 2 years of continuous use. Dump once a week,
wither it needs it or not

hankaye
Thats a good tip on turning the water on. Never crossed my mind that too much too fast could be a problem.

Thanks for the tips.
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