Water Siphoning from Full Fresh Water Tank

[Cate&Rob]

Jlawles2

Just wondering what observation you have of the water tank flexing inward when draining through the gate valve? I have not seen or heard any evidence of this through many tank draining cycles. I have an extension pipe fitted to mine, so the potential for a vortex opening up the center of the flow is not likely.

Rob

[Yoda]

My head hurts I just got my cup of coffee and started reading this. Who would have thought that this discussion would delve so deep into fluid mechanics and property of materials. When I had the belly open I discovered my 220RK tank actually has a center hole in it (could get my hand in) giving support to the top and bottom. Tank was held in place by edge channels. I could get maybe 1/2" of movement sideways and an inch or so vertical (no tie down strapping)

I filled it while it was open and it expanded about an inch overall. Full it would not budge. When I emptied it the walls sucked in about the same amount, but no air sucking. Unfortunately I did not have the back side exposed so I cold not see what the overflow was doing. To me this looked perfectly normal. Like when you fill a plastic 5gal gas can. It bows out a bit when full and returns to normal. Over time it stays slightly expanded - I can get close to 6 gallons in my 10 year old 5 gallon diesel cans now.

TucsonJim Anyway - great discussion. Maybe when the folks go back to GD they could get them to do a live test on a tank in the chassis with factory plumbing and video the siphon action when filling. Would make for a great experiment and maybe the engineers could learn something form us........well its a thought anyway.

Yep back to my corner

Keith

[Cate&Rob]

[QUOTE=Yoda;n45836]Who would have thought that this discussion would delve so deep into fluid mechanics and property of materials. [QUOTE]

It never ceases to amaze me how a bunch of engineers can very often turn a simple question into a 93 post discussion . . .

Rob

[Jlawles2]

Cate&Rob Rob what did you expect? its fluid mechanics and plumbing. Amongst engineers that like people who talk religion and politics.

[Guest]

Sometimes the theory leads to a properly performed bench test to provide verification. This would certainly solve the mystery.

I do not have a gate valve and have installed a ball valve on the overflow tube. A tee before the ball valve will be connected to the unused vent on the gravity fill that is above the water level of the tank. Since the tank drain on my Imagine is so small and flows so little, I do not see this issue at all.

For the gate valve use, there may be some collapsing of the top of the tank that traps the surface from allowing air to enter from the overflow tube. Once the vacuum increases in the tank, the top may spring up and allow air to enter the tank. No gurgling, just flow from the gate valve and outflow on the overflow which would stop and begin to let air in. Its plausible but not proof. I'm headed over to Keith's corner and will bring the beer.

Jim

[Jlawles2]

Jlawles2

Just wondering what observation you have of the water tank flexing inward when draining through the gate valve? I have not seen or heard any evidence of this through many tank draining cycles. I have an extension pipe fitted to mine, so the potential for a vortex opening up the center of the flow is not likely.

Rob

Cate&Rob Rob, My observation was in draining the 2/3rds tank that the dealer had put in the other day to do the sanitation. When opnened the gate valve I noticed (audible) that the drain was sucking air in as expected. After about 20 seconds or so I wondered how well the vent was working, so I closed the gate valve, thats when it hit me as the vent continued to pull air in for another 10 seconds. So I tried again, open listen, close and it continued. Just like a fuel can, if you pour enough out, the sides will suck in. So I then decided to only partially open the valve which helped (audible measurement only here) with the sucking of air into the vent. Patience got to me and I started opening the valve fully for a few seconds, then close back down. When the level of the water got low enough (my best guess) when i fully opened the valve the flow was different. It reminded me of a drain vortex in the bathtub (not one of those modern lift stopper ones) once the vortex center gets large enough air flows up through the center.

Someone else may try this to confirm. Unfortunately it would be detrimental to stick a camera up the vent tube, but would be interesting to see what's going on in there. I know from 1st had experience if you let a 55 gallon plastic drum drain through a garden hose with the other bung closed it will suck the drum in on itself like a crushed beer can. That was with about 3' of water vacuum.

[Jim-Dot]

I'm a new owner of a RLS303 and I just read about the water siphoning problem from the fresh water tank. My unit was built early May 2021. Does it have the modification talked about in the above posts?
Thanks

[howson]

I'm a new owner of a RLS303 and I just read about the water siphoning problem from the fresh water tank. My unit was built early May 2021. Does it have the modification talked about in the above posts?
Thanks

Cate&Rob ?

[Cate&Rob]

Jim-Dot

Grand Design reported in late April that they would begin rolling out the twin drain/vent tube design across all models. See https://gdrvowners.com/forum/operati...problem-solved No one has yet reported on this forum, about receiving a trailer with this modification. If your trailer has this change, it will have twin blue drain tubes beside the underbelly water tank drain valve. I doubt that an early May build would have this.

Rob

[OffToHavasu]

I'll volunteer my trailer to have the mod done to it and will report back. LOL

[Ray&KatinCR]

We just purchased a new 2022 Reflection 260RD and have taken it out only once where there was no water hookups. after filling the tank at home when we arrived at our camp we were down by at least a third of our water.
Somebody posted earlier about using a solenoid valve but the questions were NO/NC? and where to wire it to. suggestions included wiring it to the brake lights, using a switch that you would have to activate.
Now my memory is as bad as any on here and I know for a fact that at some point I would forget.
Our 260RD has a backup camera wired to the running lights. If I install a NO solenoid valve and wire it to the running lights, It would close when I turn on my lights so I can use the backup camera and automaticly open when I turn them off. I would install it as high as I can reach without opening up any panels so I would lose a small amount of water from the lines from sloshing etc but not a third of my full tank.

Does any one see any issues from doing this?

[mpking]

If I install a NO solenoid valve and wire it to the running lights, It would close when I turn on my lights and automaticly open when I turn them off.
Does any one see any issues from doing this?

My only comment is, I have on many occasions Dry-Camped where there is a common water fill point, and I drive up with the camper. I usually leave the truck running with the hazards on. You would need to ensure you turn the lights off when you are filling up.

I guess my point is. The NO is a cool idea, and would work in some of the cases, but not all of the use cases.

[Guest]

To prevent sloshing and to avoid damaging the tank due to over expansion (closed overflow + heating of cold water) or a collapsed tank (due to usage with closed overflow) the system must be fitted with a vent. Interesting observation while camping of a coachman with the vent connected to the gravity fill was to see water occasional spewing from the vent that was connected while he was parking on a steep grade. The vent on the gravity fill of my Imagine is not connected. To try and overcome this issue, I will run the vent line from a Tee on the overflow and before the overflow shutoff and as high as possible (underside the kitchen countertop) and back down to the vent. Some water may still make it to the vent due to sloshing but its unlikely that I will loose any real quantity of water.

I will eventually make this connection where relocating has kept with DW and I plenty busy.

Also there are methods to create a tank to prevent sloshing (baffles molded in) and with the dual vent line that Rob has come up with to prevent siphoning, this issue would be history. But the RV industry is slow to make improvements and will keep the same failure in production for years.

Jim

[Ray&KatinCR]

My only comment is, I have on many occasions Dry-Camped where there is a common water fill point, and I drive up with the camper. I usually leave the truck running with the hazards on. You would need to ensure you turn the lights off when you are filling up.

I guess my point is. The NO is a cool idea, and would work in some of the cases, but not all of the use cases.

This is my 3rd 5thwheel, first two had gravity fill ports which were a pain in the *** to add water after it was parked (I hate moving it and setting up all over again) at least half of our trips involve no water hookups. Adding water if needed seems to be pretty easy with this 260RD using the pump to draw it in. While I could stop on the way into our camp spot and top it off that would not be an issue if I don't loose 1/3 of my water just getting up there and if I need to add water I can make trips to the water fill using 5 gal jugs (Thinking of getting a bigger collapsible tank) To address your comment, the flashers/brake lights are a different circuit than the running lights so I could still use the flashers as long as I remember to turn off the park/running lights.
Ray

[Jlawles2]

Ray&KatinCR Ray, to fill my tank on the previous units that had the external fill port, I used a drum and a garden hose. Hose hooked to a boiler drain valve (because it had internal and external threads) with a draw tube to the bottom. Once the siphon was started (either suck the hose or use the tire stem in the opposing bung) I would let the drum fill the tank. If In a hurry, I would hook up the 12v air pump and let it push the water through the hose. A lot faster and only seemed to build about 5 psi in the plastic drum. Did it this way for 7 years. Now I have to figure out how to do it all over with the GD nautilus panel.