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Siphon Action Draining Water Tank - Problem Solved!

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  • #31
    I guess I still don't understand why Rob's solution fixes this issue, or why we even have this problem--unfortunately my own experience knows that all the water really does just go away. I'm not very enthusiastic about pulling the underbelly cover off until I understand this better... maybe some folks here can answer these questions... (I have a 2021 220MK)... I did fill the tank at a RV park on our last trip, to overflowing, then watched 6 gals flow out of the overflow hose. I had to get the water hauling jug out to collect it, it was making a mess at the campsite. 60 gals, - 6 gals, right? By the time we arrived at our next site, 450 miles away, the tank was < 10 gals, and the pump was not working efficiently. I had to haul 24 gals and fill through the gravity feed.
    1. During normal operation, what is venting the tank? Is it just the overflow line? If the tank is vented, why is installing a value on the overflow tank a problem?
    2. How is the gravity feed plumbed? Does it vent the tank with the vent screen? Will if vent the tank if you leave the cap off? Based on what is happening it would appear the gravity fill vent is not really hooked up, but that leaving the gravity feed cap open should serve the same purpose of the parallel overflow hose.
    3. Why don't both tubes in Rob's solution fill with water and flow out?
    4. If its just introducing air into the upper part of the plumbed overflow, could you just fish a length of aquarium air hose up the existing line until it reaches the top, and the route the free end back up high somewhere?
    - Eric P. (2021 Transcend XPLOR 200MK)

    Comment


    • #32
      epearce Welcome to the family and the forum!

      I can't provide an intelligent answer to your questions about the water tank overflow issue, but there are several threads that cover multiple explanations and complete breakdowns as to the why and how. Cate&Rob will probably stop by with a concise answer. He is the instigator for this subject.

      When you have time, the moderators have taken the time to create a Welcome Letter to help new members have the best possible experience on the forum including posting tips, how to set up a signature line and searching the forums. You can find the letter at https://gdrvowners.com/forum/main-fo...to-new-members.
      Jerry and Kelly Powell, with Halo, Nash, Reid, Cleo, Rosie, and the two newest additions Shaggy and Bella..
      Nash County, NC
      2020 Solitude 390RK-R​

      Comment


      • #33
        epearce

        Welcome to our owners technical forum. When you have a chance, have a look at our welcome post. https://gdrvowners.com/forum/main-fo...to-new-members . This will help you set up your signature and navigate the forum.

        The premise of the siphon action draining water from the tank is that because the overflow/vent tube is longer than the tank is deep (to take overflow water outside the coroplast underbelly) a column of water in this tube creates enough vacuum in the shallow flat tank to deform (suck in) the tank such that the overflow connection at the top of the tank remains submerged. A parallel second overflow tube provides a source of air to break the siphon pull in the first tube. The single outlet from the tank cannot supply enough water to keep both tubes full, so one becomes a vent for the other.

        For the siphon action to continue, the tank volume has to be decreasing (by way of the bottom and top being sucked in) to keep the vent connection submerged. It is unlikely that your tank was deformed to the point that it contained only 10 gallons. I suspect that water is getting out of your tank by some other path while you are travelling.

        For the siphon action to deform the tank, it must be completely sealed from any other source of air. Leaving the gravity fill open or providing another vent line as you mention, should accomplish the same thing. Reflections and larger Grand Design products do not have the gravity fill feature, so this is not an option. The parallel drain/vent tube is a simple way of breaking the siphon action on these models.

        Rob
        Cate & Rob
        (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
        2015 Reflection 303RLS
        2022 F350 Diesel CC SB SRW Lariat
        Bayham, Ontario, Canada

        Comment


        • #34
          The water tanks are generally long, wide, and not very tall. Losing 1 inch of water would be about 5 gallons. The vent port at 1 1/2 down from the top could drain nearly 7.5 gallons as the vent tube burped air back in to the tank. More, if the tank collapses some.
          Ted
          2021 Reflection 310RLS
          2020 F350 PS,CC,LB,SRW

          Comment


          • #35
            Thank you Cate&Rob ! "Leaving the gravity fill open or providing another vent line as you mention, should accomplish the same thing. " Simple fix for my 17mke.
            Russell and Kathy Stamets (and Lola the St Bernard)
            2021 Imagine XLS 17mke
            2015 F150 XLT 5L 4 x 4

            Comment


            • #36
              Rob, all of your pics and drawings show the overflow tube about 2" higher than the tank. On my Reflection 29rls the tank is tight against the flooring hence I could not mount my dual tubes any higher than the original position. I think this will still do the trick. It was not fun installing the tubes in the tight space. I used a dremel tool to cut the pex crimper and there was just enough space to get my crimper onto the pen fitting. I had originally installed a valve on the overflow tube but can't count the times we forgot to open the valve when we set up camp. Fortunately we always opened it before we damaged the tank. This install will give us great peace of mind and a full water tank.
              Dick and Jodi
              2020 Silverado Duramax
              2017 Reflection 27RL

              Comment


              • #37
                Originally posted by rpkramer View Post
                Rob, all of your pics and drawings show the overflow tube about 2" higher than the tank. On my Reflection 29rls the tank is tight against the flooring hence I could not mount my dual tubes any higher than the original position. I think this will still do the trick. It was not fun installing the tubes in the tight space. I used a dremel tool to cut the pex crimper and there was just enough space to get my crimper onto the pen fitting. I had originally installed a valve on the overflow tube but can't count the times we forgot to open the valve when we set up camp. Fortunately we always opened it before we damaged the tank. This install will give us great peace of mind and a full water tank.
                Did you take pics of the install , I have a 29RS as well. Have you traveled yet with the new set up to see that it does work?

                I too have installed a valve on the overflow and also have forgotten to open it.

                Brian
                Brian & Michelle
                2018 Reflection 29RS
                2022 Chevy 3500HD

                Comment


                • #38
                  Originally posted by Country Campers View Post

                  Did you take pics of the install , I have a 29RS as well. Have you traveled yet with the new set up to see that it does work?

                  I too have installed a valve on the overflow and also have forgotten to open it.

                  Brian
                  Brian I just had a thought. Right above your shut off valve on the overflow line, install a T and add a simple check valve withe flow direction reversed. Water can not get out, but air can get it. IE flow arrow towards the vent line. I don't know why I did not think of this before. It provides a path for air to enter if you forget to open the valve. The suction would need to overcome the water column, but it would not need to be that much. This would have been a simpler solution to my piping run to the front bay and I may just change that out.
                  Cate&Rob Rob - thoughts on this?

                  Keith
                  2018 Reflection 150 Series 220RK 5th whee, Star White 2022 F350 King Ranch CC Long bed (HAL) (CCC 4062lbs), B&W 25K OEM Companion,. SteadyFast system, Trailer reverse lights, rear receiver spare tire holder, storage tube, sumo springs, Victron MultiPlus 12/120/3000, Solar, Custom 6K axles upgrade, and other modifications.

                  Comment


                  • #39
                    You would need a very low cracking pressure check valve. My guess would be 1 psi or less.
                    Ted
                    2021 Reflection 310RLS
                    2020 F350 PS,CC,LB,SRW

                    Comment


                    • #40
                      Originally posted by Yoda View Post

                      Brian I just had a thought. Right above your shut off valve on the overflow line, install a T and add a simple check valve withe flow direction reversed. Water can not get out, but air can get it. IE flow arrow towards the vent line. I don't know why I did not think of this before. It provides a path for air to enter if you forget to open the valve. The suction would need to overcome the water column, but it would not need to be that much. This would have been a simpler solution to my piping run to the front bay and I may just change that out.
                      Cate&Rob Rob - thoughts on this?

                      Keith
                      Keith,

                      Like this one? I plan to connect the T to the gravity fill vent. No check valve needed.

                      Jim
                      Attached Files

                      Comment


                      • #41
                        Originally posted by Country Campers View Post

                        Did you take pics of the install , I have a 29RS as well. Have you traveled yet with the new set up to see that it does work?

                        I too have installed a valve on the overflow and also have forgotten to open it.

                        Brian
                        The picture of the double vent/drain line, included in the original description, was taken by Grand Design of their first production installation. I believe this is a Solitude tank . . . but, I am not sure of that. Grand Design confirmed the design concept by way of their bench testing. I have not installed this to try it, because we never travel with more than a few gallons of water in the tank.

                        Rob
                        Cate & Rob
                        (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
                        2015 Reflection 303RLS
                        2022 F350 Diesel CC SB SRW Lariat
                        Bayham, Ontario, Canada

                        Comment


                        • #42
                          Originally posted by Yoda View Post

                          Brian I just had a thought. Right above your shut off valve on the overflow line, install a T and add a simple check valve withe flow direction reversed. Water can not get out, but air can get it. IE flow arrow towards the vent line. I don't know why I did not think of this before. It provides a path for air to enter if you forget to open the valve. The suction would need to overcome the water column, but it would not need to be that much. This would have been a simpler solution to my piping run to the front bay and I may just change that out.
                          Cate&Rob Rob - thoughts on this?

                          Keith
                          Remember that the overflow/vent line has to allow air flow in both directions. Air has to exit as the tank is filled and enter as water is used from the tank. In your plan, you would still have to remember to open the valve when filling the tank. Forgetting the valve when pressure filling could potentially cause the most damage, taking the tank to fill pressure of something like 40 psi.

                          Rob
                          Cate & Rob
                          (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
                          2015 Reflection 303RLS
                          2022 F350 Diesel CC SB SRW Lariat
                          Bayham, Ontario, Canada

                          Comment


                          • #43
                            Originally posted by rpkramer View Post
                            Rob, all of your pics and drawings show the overflow tube about 2" higher than the tank. On my Reflection 29rls the tank is tight against the flooring hence I could not mount my dual tubes any higher than the original position. I think this will still do the trick. It was not fun installing the tubes in the tight space. I used a dremel tool to cut the pex crimper and there was just enough space to get my crimper onto the pen fitting. I had originally installed a valve on the overflow tube but can't count the times we forgot to open the valve when we set up camp. Fortunately we always opened it before we damaged the tank. This install will give us great peace of mind and a full water tank.
                            You are the first to document accomplishing this as a retrofit . There will be many waiting for your report-back on how this works.

                            Rob
                            Cate & Rob
                            (with Border Collies Molly & Angel + Kitties Hazel & Elsie)
                            2015 Reflection 303RLS
                            2022 F350 Diesel CC SB SRW Lariat
                            Bayham, Ontario, Canada

                            Comment


                            • #44
                              HI all, I am one of those that have installed a shut off valve on our 2600RB at the end of the overflow tube, this works but is a pain and another item on the check list for set up/tear down. Should I ever need to dig into the area around the gravity fill tube I will remove the existing vent/overflow, install a vent line from the location of the existing overflow on the tank, run it next to the fill tube to the existing unused screened vent outlet that is by the gravity fill cap in the same existing exterior fitting. Other than being stubborn, on the part of GD, I see no reason to provide the overflow tube on any unit with the gravity fill cap system. Sloshing, without the shut off valve, while traveling, reduces the water supply to about 10 gallons by the end of a long travel day on anything other than flat highways, that is really irritating to say the least. Not one of 4 other travel trailers we have had over the years had the overflow vent tube such as our imagine has. We had no tank damage caused by filling until water came out the vent next to the fill cap after years of doing this. Even with using the power fill option the new/old vent system should not allow enough pressure in the tank to cause damage. A solution for other units with only the power fill option is tough and the solution worked up by Rob? does seem to do the job. It would be nice for future owners of gravity fillable units not to have have to deal with this. Sorry for the bit of a rant but for those of us with gravity fill availability this is an unneeded issue.

                              Dave
                              flyfshrockies, 2021 imagine 2600RB, Ford F-150, XLT supper crew 3.5 eco boost with max tow. Dave and Toni (and the awesome Aussie Bayley, he's the social one)

                              Comment


                              • #45
                                I share 's frustration. Seems to me there should have been a separate vent and overflow, especially if the tank is that fragile. The fix is not a reasonable owner-fix, due to the difficult access, and variation between models. Will Grand Design honor warrantee after you have pulled the coroplast and modified the tank plumbing? They whole thing is disappointing.
                                All that being said, why not just modify the gravity fill cap so its vented, and put a valve on the overflow drain. Is there a one-way value on the gravity fill that would prevent it from allowing air to vent from the tank?Shouldn't this resolve the water loss issue, and not allow the tank to be pressure damaged, even if the value is left closed?
                                - Eric P. (2021 Transcend XPLOR 200MK)

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