Water siphon discussed ad nauseum. No info direct from Grand design?

[Dan P]

2021 Momentum 25G, manufacturing date 02/03/21.. I'm sorry to bring this up again but I haven't received an answer from Grand Designs. I've seen a posting on Facebook about a factory service note on the siphon issue calling for a modification to the overflow lines adding a loop to those lines. Before I brought my unit home I had my salesman call to see it my unit needed to have this procedure performed. An area rep indicated that "this issue was taken care of some time ago". Of course the first time I fill and tow down the highway it starts the siphon. I let Grand designs know that it happened and ask if the engineering change had been made to mine or if I need the modification made. The response to paraphrase was "don't overfill". But there was no mention as to when the engineering change was made, if at all! Has Grand Designs made a statement on the issue? How can I find out if the modification has been applied to my unit? I've seen all the home brew solutions but want to know if and when the problem was addressed.. Thank you.

[RobWNY]

I'm interested to learn more about this issue as well. Your tank will be empty in no time with that much water flow! When you heard not to overfill the tank, did they give a suggestion on how much water in the tank would they consider to be "over filled"

[Guest]

Overfilling the tank has little to do with this issue since tank slosh over the road will still result in a loss of water. A proper vent system and possibly a baffled tank would cure the problem.

Jim

[TedS]

Please you post the factory service note here. Curious minds want to know.

[Country Campers]

This is a known issue forever with any fresh tank, GD is no execption.
I have just returned from a Summit with GD this past week and had proposed this question to them with the following results.

The proper way to fill the tank is to fill until the tank gage inside on the convenience panel reads full. This does leave a pocket of air in the tank and slows the syphoning effect , they also said it does not stop the syphoning effect and it also does not stop the sloshing effect.
There also was know mention of a fix for this issue that was implemented at any time. They are however in the works for a fix , our very own Cate&Rob is helping with suggestions but until they are tested will not be posted here until GD gives the go ahead if owners want to modify to the new system.

The only way that owners have found to stop the syphoning and sloshing effect that causes loss of water is to either place a valve on the overflow pipe or create another overflow pipe configuration. Grand Design does not approve the use of the valve or any other type of new piping configuration, trust me on this I told them that I have been using a valve and they did not like that at all.

Hopefully when they get a new system figured out they will share so we owners can change ours to a new system that does not require us to remember to open or close a valve. The damage caused by forgetting to either open or close the valve could be very catastrophic.

Dan P

If you would please send me a PM with your VIN and the Dealer and the GD sales rep that gave you this information , please do not post it here.

Brian

[TedS]

It is not syphoning, it is draining.
GD would just need to add a gravity fill and vent arrangement. A gravity fill would be welcomed by boondockers.

[flyfshrockies]

Second that. Never had an issue with old style fresh fill with adjacent vent. Every unit I have had with the separate vent from tank had the syphon issue. Our 2600B has gravity fill but has the separate vent. While we love our GD a simple fix not implemented is a real head scratcher.

Dave

[Guest]

It is not syphoning, it is draining.
GD would just need to add a gravity fill and vent arrangement. A gravity fill would be welcomed by boondockers.

X3. I have a gravity fill and will be making the connections soon.

Jim

[Guest]

Second that. Never had an issue with old style fresh fill with adjacent vent. Every unit I have had with the separate vent from tank had the syphon issue. Our 2600B has gravity fill but has the separate vent. While we love our GD a simple fix not implemented is a real head scratcher.

Dave

Dave,

Look under your kitchen cabinet at the gravity fill. Mine is not connected but soon will be. I've installed a tee on the overflow to route a vent to the gravity fill. Below the tee is a valve that I can shut off of travel.

Jim

[flyfshrockies]

Guest Huh, guess I did not look close enough when I was peeking under the cabinet at the fill line. I put a valve on the overfill by the axel, as I did on two other units and as you have done. Did not even consider putting a second vent in the fresh gravity fill line. Am I correct in thinking that is what you are going to do or are you tapping into the pex overfill nearby? A pic, if you could get one, would clear my thinking. If you are doing what I think it leaves me feeling dense for not coming to that conclusion on my own.
Thanks

Dave

[Guest]

Guest Huh, guess I did not look close enough when I was peeking under the cabinet at the fill line. I put a valve on the overfill by the axel, as I did on two other units and as you have done. Did not even consider putting a second vent in the fresh gravity fill line. Am I correct in thinking that is what you are going to do or are you tapping into the pex overfill nearby? A pic, if you could get one, would clear my thinking. If you are doing what I think it leaves me feeling dense for not coming to that conclusion on my own.
Thanks

Dave

Dave,

I installed a Tee on the overflow that I intend on routing up through the floor, as high as I can get it and back down to the gravity fill. Below this Tee is the valve that I can open for filling and close for travel. The vent will allow for normal operation where I will not need to open the valve again until I fill to observe the overflow. Also below is a link to the locking gravity fill I intend on installing. Thinking if water does purge a bit it should not be much and with the vent protected by the cap of the locking model, the vent will remain clean. The check valve is another consideration where I hope to not need it where I would like air to move in both directions on the vent line. I'm open to all suggestions where all I really would need to do if this fails is to silicone up the 1/2" hole in the floor.

https://www.amazon.com/UKSAT-Locking...a-850101719941

https://www.usplastic.com/catalog/it...SABEgIfFvD_BwE

[flyfshrockies]

Guest Thanks Jim. I am going to review the items in your links and look around the 6 inch hole where I can see where the fresh fill drops through the floor into the tank. A great work around would be excellent as the water leaving a FULL tank is quite the irritant as we quite often need that water for extended stays and boon docking as well as prolonged road trips without camps or hook ups. Keep us posted as for progress and hoped success. Now that you stirred my pot I was actually thinking of just tapping the fill line to add a vent that reached higher than needed and letting it vent behind the cabinets. I am thinking it would require a lot of slosh to force water 2 feet above the tank in that vent line? Maybe a one way valve that intakes air only would improve that idea. I have never had the water from a full tank come out of the vent that was provided next to the fresh fill with any other units. Just thinking that a locking fill cap might be required gives me the willies thinking of that implication.

Dave

[ncitro]

I was able to run my overflow rearward and up and mounted the vent on the back wall (well above the tank). This allows for gravity to keep the overflow clear of water, and its difficult for sloshing to establish a siphon since it is uphill. It has been about eight months and has been flawless so far. I used a holding tank roof vent to mount it.

[Guest]

Guest Thanks Jim. I am going to review the items in your links and look around the 6 inch hole where I can see where the fresh fill drops through the floor into the tank. A great work around would be excellent as the water leaving a FULL tank is quite the irritant as we quite often need that water for extended stays and boon docking as well as prolonged road trips without camps or hook ups. Keep us posted as for progress and hoped success. Now that you stirred my pot I was actually thinking of just tapping the fill line to add a vent that reached higher than needed and letting it vent behind the cabinets. I am thinking it would require a lot of slosh to force water 2 feet above the tank in that vent line? Maybe a one way valve that intakes air only would improve that idea. I have never had the water from a full tank come out of the vent that was provided next to the fresh fill with any other units. Just thinking that a locking fill cap might be required gives me the willies thinking of that implication.

Dave

Dave,

I didn't notice the hole for the fill line was that large. Thank you where I can pull the insulation and add in the vent hose along side and re-insulate. I would not recommend leaving an open vent line inside the rig since enough hydraulic pressure from sloshing may end up with water on the floor. The check valve installed to allow air in and prevent water from exiting would work, but we would need to be sure to not fill the tank too much since there should be some space for expansion. I am starting with the vent line attached to the locking gravity fill vent to see how this works.

The locking gravity fill will primarily be used due to the vent being protected from road debris, rain and so on. The secondary benefit is to protect our water supply.

Jim

[Jlawles2]

Guest Jim, Why not take one of the high point vacuum breakers (vented loop) like in the other post and just route the line back to where it came from? Put one of the AAV vents on the top of the breaker. https://www.homedepot.com/p/STUDOR-R...0353/203111264 is a one way valve. Lets air in but not air or water back out.

https://www.amazon.com/Five-Oceans-O...86078675&psc=1

It looks like they have the AAV built into the top of a few of them.