Fresh Water Tank Overflow - Revisited

[howson]

Reading through the threads it looks like the valves added to the end of the overflow valves are being closed while water is still running out of them...

I can only say what I do--I turn off the water then close the valve. If there's water going in (or out) of the water tank the valve is open. The only reason it's closed is to keep from losing water (a common problem) while towing. I rarely fill my water tank all the way, but if I do I'll stop at 40 gallons so I don't have to mess with "burping" the tank.

My question is that if the water supply is shut off when water starts flowing out of the overflow, and the valve on the overflow is left open until water stops flowing out the overflow...

That's the problem, Bill. The water doesn't stop flowing because equalization (that's what stops a siphon) doesn't happen until the tank is significantly collapsed. What Jim describes in post 1 happened to me at a campground once (before I installed the valve) and couldn't figure out how to get the water to stop flowing. Since I've done a LOT of work on my system I understand how it works, thus was able to figure out a solution to get air in the tank without adding another vent. The owner must have a Nautilus-equipped trailer, obviously. Not sure how to break the siphon on an Imagine or similarly equipped trailer.

[steve&renee]

(The red "V?" is a reminder to check the overflow valve and ensure it's open. I have a sticker at the Convenience Center pump switch, too.)

Howard

Here's my red "V?". (Courtesy of some guy who used to work on jets.)

[TucsonJim]

We're heading out tomorrow for a weekend jaunt, so I decided to fill up the water tank to see if I could repeat the results. Cause we engineers know that repeatable results are easier to deal with... So I told myself to "get a couple of five gallon buckets so you can measure how much drains out". [I like to boss myself around like that].

I filled the tank until there was a good stream of water flowing out of the overflow tube. I shut off the water supply, and slid a bucket under the tube and started measuring. "What The Hey!!!" only 1/2 gallon of water spilled out, and then it completely stopped. .. I filled it exactly the same way as I did the last time, in exactly the same spot, with exactly the same hose. Maybe the molecular density of the water was affected by the Coriolus effect and geothermal resonance. In other words, I'm clueless.

Okay, so next, I tried pushing in on the little check valve button thingy in the water connection like Howard suggested. I could hear gurgling that sounded like like some of my buddies after eating the six day old chili and drinking warm Bud Light.

I will get to the bottom of this, but now it's time for some chili and beer.

Jim

[Canyonlight]

We're heading out tomorrow for a weekend jaunt, so I decided to fill up the water tank to see if I could repeat the results. Cause we engineers know that repeatable results are easier to deal with... So I told myself to "get a couple of five gallon buckets so you can measure how much drains out". [I like to boss myself around like that].

I filled the tank until there was a good stream of water flowing out of the overflow tube. I shut off the water supply, and slid a bucket under the tube and started measuring. "What The Hey!!!" only 1/2 gallon of water spilled out, and then it completely stopped. .. I filled it exactly the same way as I did the last time, in exactly the same spot, with exactly the same hose. Maybe the molecular density of the water was affected by the Coriolus effect and geothermal resonance. In other words, I'm clueless.

Okay, so next, I tried pushing in on the little check valve button thingy in the water connection like Howard suggested. I could hear gurgling that sounded like like some of my buddies after eating the six day old chili and drinking warm Bud Light.

I will get to the bottom of this, but now it's time for some chili and beer.

Jim

And remember.....Bud Light is not beer !

Dan

[TucsonJim]

And remember.....Bud Light is not beer !

Dan

I try to tell some of my low-life friends this, but they'll never change. I'll be drowning this one with Deschutes Royal Fresh IPA...

Jim

[Yoda]

...This tells me that the tank is collapsing and no air can enter the tank until it finally gets low enough on water for the suction to stop. Next week, I'm planning on dropping the coroplast for some other work and I'll work on developing a method for proper tank venting if I can. In the mean time, I need to make sure to leave an air space at the top of the tank while filling.

When I had my belly open I noticed my water tank had a round void cast through the the middle. I did not measure it but probably 4" dia. I an guessing this is to prevent tank collapse or reduce sloshing. However with my vent set up I have not had your sucking air issue. Now you have me thinking after using the pump for a day I should open the drain and see if I get the sucking sound as the water in the line may be more than the tank can draw back to vent. I'm winterized so cant try and duplicate this. Plus is cold.

There was someone that posted getting the same sound - he was trying to stop water loss while traveling, but he claimed none of the ideas worked for him. I think it was posted in my original thread on my solution. Might be here or at the other place.

There is one other thing to think about. In howson Howard's picture I cant tell how the tank is oriented when installed, but the tank looks pretty long. My thought is if the tank is off level, a heck of a lot of water can run out until it gets to below the vent outlet which appears to be about an inch below the top. Now if I do my math correctly (water is 7.48 Gallons per CUFT) assuming the tank is 4' by 6' that's 14.96 gallon per inch, If the tank collapse another inch that's 28 gallons . So Jim if you were justly slightly out of level when set up a lot of water might need to exit the tank to get the overflow fitting uncovered. Depending on the room above the tank, a T and the air/vac above the tank should work - but it does spit water as it cycles so some way to drain out will be needed.

Makes me think folks need to use about 10 gallons of water or more before opening the valve if it keeps draining.

[Yoda]

TucsonJim & Others. I have fought this issue from day one on my 28BH. I went through several permutations, I started with the valve on the overflow, it worked fine, but my memory did not. I attempted to move the valve rearward so I could access it easier with the slide out (for when I inevitably forgot to open it two days into camping) but that caused the described issue with water in the vent pipe not allowing air to flow. I solved this by using my Dewalt leaf blower to push the air into the tank so it could breath effectively, still not ideal. My next revision was the solution described in the other place with the vent run forward to the propane compartment, and a vacuum relief valve and a low point drain. I had limited results with this as well. I determined as mentioned above that the tank was simply too flexible to have enough suction to pull pretty much any water in the vent line back into the tank. Instead it was just "easier" for the tank to collapse on itself. I am sure I did not do this any favors by forgetting to open the valve. I dropped my coroplast looking for a solution, and actually removed my fresh tank. It was the flimsiest thing I had ever seen in my life. Even when full I could compress it by hand with very little effort. In my rig it was supported by steel straps underneath, and between each strap a belly formed with only a very small amount of water, which got worse as I added water. I shortened the straps hoping that might help, but it did not do much.

The vent line comes off the side of the tank towards the top as Howard shows, but it then immediately goes into two elbows to get it pointed down to the ground. What I finally did was remove the existing vent entirely, and run it at the top of the underside rearward. I then elbowed up and onto the back wall where I installed a roof vent (with a piece of screen inside to keep bugs out). Now it runs uphill from the tank all the way to the vent. I fill until water comes out, and when it stops as I use water gravity drains the water in the vent line back into the tank and it breaths normally. Not the most beautiful solution, but it works awesome and is totally automated. I have done three weeks in the rig with it, with no issues so far.

I will be back at the rig this afternoon and will take a photo of the vent on the back, but it pretty much looks as you would expect.

Neil - did you change the fitting location to the top, or just the way the vent pipe ran? I think I know what you did, but just cant picture it.
Thanks
Keith

[ncitro]

Neil - did you change the fitting location to the top, or just the way the vent pipe ran? I think I know what you did, but just cant picture it.
Thanks
Keith

Kept the fitting in the same spot, it sits up against the under side of the floor so no way to move it to the top of the tank. I came out of the vent fitting and immediately started running it uphill towards the rear of the rig with no valleys. Sorry didn’t make it over for a picture today, should be there tomorrow.

[JBill9694]

I can only say what I do--I turn off the water then close the valve. If there's water going in (or out) of the water tank the valve is open. The only reason it's closed is to keep from losing water (a common problem) while towing. I rarely fill my water tank all the way, but if I do I'll stop at 40 gallons so I don't have to mess with "burping" the tank.



That's the problem, Bill. The water doesn't stop flowing because equalization (that's what stops a siphon) doesn't happen until the tank is significantly collapsed. What Jim describes in post 1 happened to me at a campground once (before I installed the valve) and couldn't figure out how to get the water to stop flowing. Since I've done a LOT of work on my system I understand how it works, thus was able to figure out a solution to get air in the tank without adding another vent. The owner must have a Nautilus-equipped trailer, obviously. Not sure how to break the siphon on an Imagine or similarly equipped trailer.

Thanks for the clarifications, Howard. I think we and the others can agree that the main goal is to not fill the tank all the way full. Whether this is by measuring the water flowing into the tank or by shutting the flow off as soon as water starts coming out of the overflow is like most things a personal choice of the owner. I will note that I do have an auxiliary fresh water tank that is being filled at a slower rate at the same time I'm filling my main tank, which would complicate trying to measure the flow. It could be done, it would just be be a little more complicated. I think I'll stay with my method but will keep in mind the manual depression of the check valve at the water inlet if I do get too much flow from the overflow tube.

[howson]

I think I'll stay with my method but will keep in mind the manual depression of the check valve at the water inlet if I do get too much flow from the overflow tube.

Completely agree! There's no right or wrong method, just alternatives. (FYI, I'm going to stop filling at 40 gallons should I need to fill my tank.)

For those that are wondering why depressing the check valve works to equalize pressure when the Nautilus is set to PowerFill, the schematic below is how I believe the system works. Follow the blue "water" as it flows from the City Water connection all the way to the Potable Water tank. It's allows a pressure differential to dissipate between the outside of the tank and inside (bypasses the water pump).



All of the diagrams (Nautilus Panel settings) are in the Plumbing > Reference Material channel in post #5 of the Nautilus P1 Panel Information thread: https://gdrvowners.com/forum/operati...=4598#post4598

Howard

[Guest]

This is another thread where there will be many solution to this issue from a wonderful group of problem solvers.

For my rig I've planned for some time on adding a couple items to solve this issue. But traveling back and forth to Ohio to help my aging parents is consuming my spare time. Worth it I should add.

I've prepped this long ago and will at some time connect a tee from the overflow to a new locking gravity fill vent line. This way, I can use the overflow to fill, close it off and leave it off. The small air vent will handle all the water usage since {mdot In = mdot Out} (one for Rob) where the density of air is much lighter than water so the air vent can be much smaller than the overflow line that from Jim's discovery can be water trapped.

Plan for my 2600RB

1) Add a locking gravity fill with a protected vent. Many do not have a gravity fill where the vent can be ran elsewhere as long as its a clean location and high enough to protect from tank slosh.
2) Connect the Tee on the overflow to the gravity fill vent.

https://www.amazon.com/Gravity-Locka...148682423&th=1

There are many ways to skin a cat (catfish) where I believe this will work for me.

Jim

[ncitro]

Here are photos of the “roof vent” I placed on the rear of the rig. I was able to adapt up from the 3/4” vent line coming off the tank to vent fitting. I put some window screen between the vent and the cap to keep critters out, and it’s pitched in such a way that no rain or splashed water should get into it. I’m happy so far.

[TucsonJim]

Okee dokee. I'm back from a short camping trip this weekend. As I mentioned before, when I filled this time, the overflow pipe sucked air and I only lost a very small amount of water. I traveled with the add-on valve closed and when I got camp set up, I opened the valve and there was zero spillage.

The primary difference between this time and the last time (when it wouldn't vent) is when I shut off the water. A few weeks ago, the water ran out of the overflow for a good 30 seconds before I shut it off. This time it was shut off as soon as I saw the first little bit coming out.

Several of you have alluded to the fact that overflowing to the point of removing the air space can cause the suction/siphon issue. It sure looks that way.

Jim

[Guest]

Huntindog

Part of this issue is also the slosh that occurs while traveling. Similar to what you stated, I plan to connect a vent line to my installed Tee, go up through the floor and as high into the kitchen cabinet as possible then back down to the gravity fill vent. Once my overflow ball valve is closed, I will leave it closed until the next fill.

Excellent looking Brittany by the way. I miss my Brittany terribly.

Jim