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Old 12-17-2013, 10:32 AM   #1
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WARNING with a BIG W



Hello everyone.

I was filling up my fresh water tank yesterday and was shocked when I heard a loud "woomph" similar to the sound gas makes when it ignites. The dog went crazy and thankfully Dear Wifey was sitting on the beach when it happened.

What the heck happened? I said or words to that effect!

I had previously installed a one way check valve on the front overfill and a ball valve on the rear one to minimize the siphoning effect. I'm sure you can see it now! The front check valve did not open...either because it was defective or had failed or I installed it incorrectly. I had forgotten to open the ball valve after the last fill I reminded myself to do so several times, usually in the middle of the night. So the end result is that the tank ruptured. Most is around the dump valve and the neck of the exit of the tank.

I may be lucky and may be able to weld the holes by the tank neck fitting with the Flex Set or the Tap poly weld. This is assuming that there is not a huge gaping hole on the top or sides of the tank . The problem right now is that we are boondocking and I don't know if I can get the materials to do the repair or not.

Just wanted everyone to learn from my huge mistake and know that if you do tamper with the overfills ....PLEASE BE CAREFUL.

Geoff
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Old 12-17-2013, 01:53 PM   #2
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Originally Posted by alpinedrvr View Post


Hello everyone.



I had previously installed a one way check valve on the front overfill and a ball valve on the rear one to minimize the siphoning effect.
the end result is that the tank ruptured.
Just wanted everyone to learn from my huge mistake and know that if you do tamper with the overfills ....PLEASE BE CAREFUL.

Geoff
Geoff
Good warning!

A RV fresh water tank needs an exhaust vent, to allow the air in the tank to exit/escape while being filled with water.
It also must have an intake vent to allow makeup air in as the water pump draws water out.
As you have found, modifying tank vents leads to trouble.
Mel
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Old 12-17-2013, 03:04 PM   #3
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Rather than a check valve or shut off valve to prevent siphoning, I suggest putting a vent hose that loops as high above the tank as you can get. The hose can then end under the RV. Now you'll have to prevent siphoning, caused by the weight of water in the down side 'pulling' the water up the hose and out of the tank. The way to to this is to poke a small hole in the top side of the hose at the top of the loop. This prevents siphoning because the air is drawn in and stops the water from flowing. Unless you seriously allow the tank to overflow, water will not come out of the hole but instead will flow past and down to the end.
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Old 12-17-2013, 03:09 PM   #4
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Think I'll just stick with losing a few gallons due to siphoning !
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Old 12-17-2013, 03:11 PM   #5
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I put a vacuum breaker and a valve on the front vent, but nothing on the rear, which never had a siphon problem anyway. Never have had a problem draining or filling since, and it has been 5+ years now. I saved over 35 gallons from siphoning out, so the change was well worth it. But you definitely need to be aware of what you are doing, and never block both vents!
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Old 12-17-2013, 03:19 PM   #6
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The other thing to watch for on vent hoses is a P trap effect; water fills that trap and then you get no more venting.
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Old 12-17-2013, 05:05 PM   #7
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Thanks for all the comments and suggestions. I took off the drain dump valve and found a cap to screw onto the neck of the tank. Didn't work. I can see where the welds around the neck have been stressed and are leaking. When I screw in the cap it goes to a certain point and then pops out as I think there are probably cracks in the neck and threads as well. I tried a clamp around the neck to keep it rigid to no avail ...still leaking. I called Carolyn at Aubrey's RV and she is checking for a tank. In the meantime I am thinking of cutting out the neck fitting on the tank and the welds that are leaking and gluing a piece of plexiglass or poly and put supports under the whole thing and see (as the expression goes) if that will hold water .

Geoff
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Old 12-18-2013, 07:59 AM   #8
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Originally Posted by BFlinn181 View Post
Rather than a check valve or shut off valve to prevent siphoning, I suggest putting a vent hose that loops as high above the tank as you can get. The hose can then end under the RV. Now you'll have to prevent siphoning, caused by the weight of water in the down side 'pulling' the water up the hose and out of the tank. The way to to this is to poke a small hole in the top side of the hose at the top of the loop. This prevents siphoning because the air is drawn in and stops the water from flowing. Unless you seriously allow the tank to overflow, water will not come out of the hole but instead will flow past and down to the end.
BFlinn181

Great suggestion!

In marine, (aka: boat), applications they use a "duck bill valve" at the highest point of the loop of hose.
A "duck bill valve" does not leak under pressure but allows air in to prevent siphoning.

Mel
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Old 12-18-2013, 12:25 PM   #9
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That duck bill valve, soft rubber lips that press together under ordinary conditions, sounds good. Later WRV plumbing schematics show a tall inverted U for this anti siphon feature, but no fitting at the top. I'm guessing that U is behind the shower. A simple tee @ top of theU with the leg facing up with the duck bill, a cap with small hole or similar would be a nice addition if anyone has to take the shower out for any other reason.
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Old 12-18-2013, 07:59 PM   #10
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Mike have youheard of any problems with generator slides not working mine only goes in and out 1/8-1/4 inch turning switch of an on unhooked worm from motor and turns just fine cant see anything that would make it stop unless motor with aload is no good any ideas Robert Slocum 37ft
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Old 12-18-2013, 08:55 PM   #11
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Mike have youheard of any problems with generator slides not working mine only goes in and out 1/8-1/4 inch turning switch of an on unhooked worm from motor and turns just fine cant see anything that would make it stop unless motor with aload is no good any ideas Robert Slocum 37ft
Check for a pin or a bolt in the slide to prevent accidental deployment of the generator when you don't want it out.
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Old 12-24-2013, 09:41 AM   #12
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Short update on my water tank.

I got on touch with Carolyn at Aubrey's and she has a water tank but it is longer than mine by about 10 inches. I have ordered some Marinetex Flex Set and will try that when I get it. If that doesn't work then I will see if the longer tank will fit somehow. Probably won't have more news until the new year!

Everyone have a Merry Christmas

Geoff
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Old 12-24-2013, 12:45 PM   #13
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There's a company in (michigan I think) called Trionics, that builds poly tanks for the Marine Industry in about any configuration you can think of. Very heavy duty, I've had one on my boat for years. Excellent product. Google it and see what they can do.
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Old 12-25-2013, 02:31 AM   #14
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You are not the only one to blow a water tank trying to prevent siphoning. If there is only one vent, which is what I would expect, air has to flow both ways so no check valve (and a duck bill is a check valve) should be installed. A manual valve is not a good idea either because you will forget to open it. On my 07 34FDDS the water tank is bolted up to and under the floor so I don't see how the tank is vented. If I overfill it, water runs out of one of those drains that go through the compartment floor but it is part of a rat's nest of plumbing. If the vent was attached to the top of the tank, siphoning would be impossible. What you may observe is just splash from a full tank. Could not be more than a few gallons.
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