Can rough roads create a suction from the water tank vent?

[Pangaea_Ron]

I have been driving some windy and hilly roads on Highway 101 on the Oregon Coast with the MH, and it seems that I have lost water from the water tank. Can surging water in the tank leak out the vent tube and create a suction that would drain water from the tank? It seems to do that if I overfill the tank?

I noticed that a bit of water was dripping out the vent tube when I stopped at a view point.

[dewey02]

Don't know how this works for other RVs, but for Jayco & Starcraft, it is a well known problem. They have overflow tubes that extend below the tank and can easily lose 1/2 the volume of water on the way to a campground, and you don't even need to be on a bumpy road. Problem is solved by putting a valve on the overflow tubes. Pressure is not a problem because they also have a vent tube located up high adjacent to the fill tube. You just have to remember to keep the valve on the overflow tube open when filling. Once you get full and water starts coming out the overflow, close the tube. Don't have to open it again until next time you fill. Problem solved.

[rbturner]

We had a 2000 Holiday Rambler; Aluma-lite that would drain 3/4 of the water out via the overflow tube. The tube was installed into the tank within 3" of the bottom. Once you got the siphon started she would run down until it sucked air. Several times we left home with a full tank and got to the campsite with a quarter tank left.

I fixed it by getting rid of that pile of junk.

[tpi]

Pangaea Ron wrote:
Lynnmor

I agree about the check valve, thus my earlier question about pressurizing the tank. Upon thinking about it, even a plug should have a small hole to allow the tank to vent for expanding water, etc. I might (probably would) forget to remove it for use.

Re-routing the line seems to be the best option.

At least there has to be some kind of provision for venting pressure. Elevation changes come to mind and can create a considerable pressure or vacuum situation.

[kampinguru]

Beartoo wrote:
I installed a valve to close the over flow after I fill the tank.

Me too. I would lose 1/4 of my holding tank to this.

[Pangaea_Ron]

Lynnmor

I agree about the check valve, thus my earlier question about pressurizing the tank. Upon thinking about it, even a plug should have a small hole to allow the tank to vent for expanding water, etc. I might (probably would) forget to remove it for use.

Re-routing the line seems to be the best option.

[Lynnmor]

If you pressure the tank, DO NOT use a check valve, you may expand the tank. The vent must exit the coach well above the tank level. Many RV's of late are not installing the vents high enough or, even worse, under the coach.

[Pangaea_Ron]

I like the ideas about check valves and an extended vent line. I think that I'll try to extend the vent line to the side of the MH from its center location (so I can easily get to it) and provide a loop or high spot. I'll try a plug or valve it that doesn't solve the problem.

Thanks, Ron

[SeaDog_BRR]

I had this problem with the winnie when I was not parked on the level and water syphoned out the overflow/vent. My fix was to extend my vent pipe to the rear storage compartment up to the overhead of the compartment and then back down thru the floor. Solved the water problem and lets me fill the tanks full without loosing water while driving or when parked on an angle.

[path1]

I too have this problem and here is what I thought might work but never followed up on actually installing them. Was thinking about some type of check valve in fill tube and vent. For vent line I thought this would workhttp://www.tibesti.com/shop/SHURflo-340-001-In-Line-Check-Valve/7UDQTY999Y and for the filler tube (big hose) http://thespaworks.com/parts/cal-spa-parts/valve-parts/cal-spa-2-inch-flapper-pvc-water-check-valve
But don't know if these products are designed to work from gravity for incoming water or actual water pressure against the flapper part of valve. Would these check valves solve the problem?
Then I thought about putting in plastic ball valves, but don't like idea of getting under the table and lifting up seat to open and close valves when filling each time and thought check valve would be better??????

[Captain_Obvious]

Beartoo wrote:
I installed a valve to close the over flow after I fill the tank.

I did this mod too once I figured out that almost 1/3 of my water would slosh out on the drive. I always fill the tanks before heading out because we almost exclusively boondock.

[BruceMc]

Pangaea Ron wrote:

I like the idea of a plug or valve in the vent tube while underway. Are there any issues with pressurization while using the pump?

The main fill cap is not air-tight, so it lets in enough when pulling small amounts of water.

I changed the cap retainer so that it attaches to the cap via a nylon bolt through the cap, then double nutted. The bolt spins in the hole, but the double nuts hold the retainer strap. I did this primarily so it would provide and additional bit of an air inlet into the tank while the ventline was plugged yet would not allow much water to slosh out. It seeps a bit, but that's ok.

[Artum_Snowbird]

I had such a problem with this, I found a way to extend both the fill pipe, and the overflow pipe by putting in a hollow tube and then another tube down to a half gallon empty pop bottle for each tube.

In a 1/4 mile drive around the block, the main fill tube had overspilled through sloshing and almost filled the water bottle, and the overfill tube had spilled and filled about 1/4 of the water bottle.

After that, I plugged the fill tube (the main culprit) and extended the overfill tube much higher so it would not spill out of it and still release water when I pumped it out of the tank.

[tpi]

I get some slosh and spill from the vent with full tank. Other than some hard water spots I clean off now and then, it doesn't seem to lose a significant amount of water. It is more of a minor nuisance-a few square ft. of water spots which need to be cleaned occasionally.

[wa8yxm]

In a properly designed and built system the answer is NO.

However... if you fill up the water temp in the tank is generally approaching sixty degrees (normal tap water) and you may be... Well the outside temp is 81 here when I parked (Cooling off as it gets dark) Water expands when heated EXCEPT at the freezing point. (absolutely unique in that "Except" no other material exhibits that expanding when freezing).

Thus the tank, if filled, WILL overflow as it warms.