First Trip, Fresh Water Tank Issue

[guest2]

I’m perplexed by all this “siphoning” from the tank vent stuff. I’ve had numerous rv’s with and without gravity fills and never had more than a gallon or so slosh out during travel. The tank vent should be near the top of the tank. If any siphoning were to occur, as soon as the water level was below the vent it would stop siphoning. There must be some kind of underlying issue here.
Also, sealing up the water tank is a good way to promote algae and mold.
Rich

[Cate&Rob]

guest2 See the first post of this thread https://gdrvowners.com/forum/operati...problem-solved Basically, water filling the overflow tube, which is longer than the height of the tank, can create enough vacuum to draw in the top and even lift the bottom of the tank, thus reducing the volume of the tank and keeping the connection to the overflow submerged. Hard to believe . . . but, this was my theory . . . subsequently proven through bench testing at Grand Design. This is what led to the twin overflow pipes to break this vacuum.

Rob

[TedS]

It could also be solved with oversized overflow tubes that will not flow full to not create the suction. And putting the vent port on the top of the tank instead of high on the side.

[Cate&Rob]

TedS There could certainly be other solutions. Even running the overflow tube down on an angle could allow air to break the vacuum. From a production perspective, Grand Design was interested in a fix that required a minimum number of parts already in the plant and that did not require specific installation instructions like angling the pipe down at a prescribed angle.

Rob