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 7/8/2010 12:41 AM
 

I have 2 vents on my fresh water tank. One under chassis suspect from top of tank. The other one is at the filler opening where I can pour in water. My question is may I plugged the one under the chassis? I loose plenty of water when drivng down the road. We do a lot of dry camping. I think the vent at the fill spout will do. Any ideas or suggestion welcome. I think I could hold more water if it was plugged because after I fill it and turn off the water it continues to drain. Thanks in advance..


Stutz Pasco, Wa
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 7/8/2010 6:17 AM
 

I've been wrong before but I've never heard of an open vent directly on a water tank. Perhaps this should actually be attached to a vent pipe that exits through your roof. Its sounds like either this was never glued or was poorly done and has become detached. The filler vent is not large enough to allow proper operation. When you put the cap on your filler opening, it should close that vent which is really just there to allow proper filling.


Libby and John and RV the CAT Ford F 150 towing a 2017 Forest River Vibe 277 RLS Click here to see our current location
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 7/8/2010 8:31 AM
 

stiltz49 - The line running from the top of your fresh water tank and exiting under the chassis isn't a "vent", it's the tank's overflow line and it wouldn't be a good idea to block it. The reason you're losing water is because you're filling it to the top and once the water starts flowing through that line it starts a siphon and continues flowing until the water in the tank gets low enough to break the siphon. Depending on how much the top of your tank sags as it empties, this could result in losing almost a third of the water. This is a common plumbing problem and can be easily corrected by creating an air break in the line at a point above the tank. Good luck. - Dave

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 7/9/2010 1:32 AM
 

stiltz49

Great post. I agree with RVA; it's your freshwater overflow. Surely you know how to create an air break in the line above the tank, right?

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 7/9/2010 2:24 AM
 
 Modified By RVA  on 7/9/2010 1:57:39 AM

Tex - Thanks, I may have assumed too much. Below is the "air break" I installed on my MH to stop the fresh water from siphoning out.

1) The gray pipe is the tank overflow line, and originally it was one piece that ran from the top of the tank and exited under the coach. This arrangement allowed the water to be siphoned from the tank whenever the tank was filled to overflowing.

2) I cut the gray pipe and connected it to an elbow and a short piece (3") of the pipe I cut off.

3) The portion of the original gray pipe that went under the coach was replaced with a section of PVC piping (The inside diameter of the PVC must be bigger than the outside diameter of the gray overflow pipe.). It was easy to install, since it fit through the hole already in the flooring for the original piping.

4) Position the PVC pipe so it's as high above the top of the tank as possible, and insert the small section of gray pipe connected to the elbow. The connection should be loose, so secure the lines so it won't pop out.

This "air break" arrangement will provide overflow protection while making a siphon impossible.

Good luck. - Dave

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 7/9/2010 4:36 PM
 

This in a Motor Home and I can not gain access to the overflow/vent out let. I have no choice I guess is to forget it or plug it and take the gravity cap off when filling it and then hope the vent at the gravity cap lets air in the drain tank. Thanks again for all comments and ideas.


Stutz Pasco, Wa
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 7/12/2010 11:47 AM
 

The instructions that came with my coach are to always remove the gravity fill cap when filling the fresh water tank via the city water hookup and the diverter valve. RVA is correct in that you are dealing with a tank overflow line and a siphon problem, but taking off the gravity fill cap and not filling the tank to 100% should stop the problem.


Dutch '07 Allegro Bay 34' '09 Honda Fit Sport Whatever hits the fan will not be distributed evenly
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