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

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.

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.

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.

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.

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.

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.

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

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.

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??????

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.