Cause of Fresh Water Puking

[JRD]

Much has been written on this forum about fresh water puking from the vent/overflow hose(s) during fill up and the various fixes used. I've read most of them - thank you all - but haven't been able to answer the fundamental question:

What is the cause of the siphoning problem from the fresh water tank?

1. Why does water siphon from the tank when the vent/overflow hose is arched (curled) above the level of the tank and down through the underside? Assuming the hose doesn't extend down into the tank, this seems to defy the laws of physics.

2. Why is the screened vent hole next to the filler tube opening plugged at the factory and not being used as the vent? This is the case on my WH 24RKS but may not be true of all. Our former TT used this system instead of an arched hose with no problems.

JRD

[dewey02]

Originally Posted by JRD

What is the cause of the siphoning problem from the fresh water tank?

1. Why does water siphon from the tank when the vent/overflow hose is arched (curled) above the level of the tank and down through the underside? Assuming the hose doesn't extend down into the tank, this seems to defy the laws of physics.

2. Why is the screened vent hole next to the filler tube opening plugged at the factory and not being used as the vent? This is the case on my WH 24RKS but may not be true of all. Our former TT used this system instead of an arched hose with no problems. JRD

These are topics for "Heavy Mystery Time"

https://www.youtube.com/watch?v=thEy0ZtNe8s

[JRD]

Fundamental questions, as I said.

[DanNJanice]

Originally Posted by JRD

Much has been written on this forum about fresh water puking from the vent/overflow hose(s) during fill up and the various fixes used. I've read most of them - thank you all - but haven't been able to answer the fundamental question:

What is the cause of the siphoning problem from the fresh water tank?

1. Why does water siphon from the tank when the vent/overflow hose is arched (curled) above the level of the tank and down through the underside? Assuming the hose doesn't extend down into the tank, this seems to defy the laws of physics.

2. Why is the screened vent hole next to the filler tube opening plugged at the factory and not being used as the vent? This is the case on my WH 24RKS but may not be true of all. Our former TT used this system instead of an arched hose with no problems.

JRD

Some have argued that the siphoning does not exist, that it has to be something else. Usually, these are the people who do not have the issue or who always use full hookups.

1) How do you know that the hose is arched above the tank and does not extend down into the tank? A lot of the trailers that have this issue are ordered with the "elite" package (like mine) so the underbelly is closed and I have no idea what the plumbing looks like.
2) I think it has to do with the larger water capacity option, which is actually two tanks and so the second tank would not be vented unless they came out the bottom.

I admit, both of these hypothesis are weak at best.
Someday, when I have nothing better to do, I will take off the underbelly cover on my trailer and all the mysteries will be solved.

[Levinehikeski]

So, why don't you unplug the screened vent hole, plug or take out the hose in question and your system would work like your previous one?

[JRD]

"1) How do you know that the hose is arched above the tank and does not extend down into the tank? A lot of the trailers that have this issue are ordered with the "elite" package (like mine) so the underbelly is closed and I have no idea what the plumbing looks like.
2) I think it has to do with the larger water capacity option, which is actually two tanks and so the second tank would not be vented unless they came out the bottom."


Luckily, I can see the pump and connections to the top of the tank in the space under a dinette seat. The overflow is arched about 4-6" above the tank but lower than the fill tube. It's a single 42 gallon tank with one overflow. Looks like it should work properly, but...

[JRD]

I'm with you, Levinehikeski. That's on my list of possible remedies. But again, I wonder why Jayco plugged the vent and didn't use it in the first place.

It's a new TT so ideally my dealer would fix this under warranty. Here are the possible solutions I'm considering:

1. Add a piece of hose to extend the arch of the vent/overflow 12" above the floor which would get the top of the arch just above the filler hose inlet. There's enough space under the dinette seat to do this.

2. Run the existing vent/overflow hose to the screened vent by the filler inlet instead of through the floor and underside.

3. Install a valve at the end of the vent/overflow as many on this forum have done.

I'm considering options 1 and 2 first because they maintain the principle of the original system and there is a big CAUTION box in my owners manual regarding closing off the vent tube. Both of these options assume that the vent/overflow hose doesn't extend down into the fresh water tank.

Of course, none of these fixes get to the root of the problem: why do our tanks siphon when the arched vent/overflow looks like it should work?

[DanNJanice]

Originally Posted by JRD

I'm with you, Levinehikeski. That's on my list of possible remedies. But again, I wonder why Jayco plugged the vent and didn't use it in the first place.

It's a new TT so ideally my dealer would fix this under warranty. Here are the possible solutions I'm considering:

1. Add a piece of hose to extend the arch of the vent/overflow 12" above the floor which would get the top of the arch just above the filler hose inlet. There's enough space under the dinette seat to do this.

2. Run the existing vent/overflow hose to the screened vent by the filler inlet instead of through the floor and underside.

3. Install a valve at the end of the vent/overflow as many on this forum have done.

I'm considering options 1 and 2 first because they maintain the principle of the original system and there is a big CAUTION box in my owners manual regarding closing off the vent tube. Both of these options assume that the vent/overflow hose doesn't extend down into the fresh water tank.

Of course, none of these fixes get to the root of the problem: why do our tanks siphon when the arched vent/overflow looks like it should work?

Is there any way you can watch the water level in the tank while it fills? If water starts coming out of the vent tube before the tank is filled, that will answer your question. I wish I had access to mine, I would probably re-route everything to make it work as it should.

[JRD]

Yes, I can see the top of the tank through the ~6" cut outs in the floor under the dinette seat. I will certainly monitor that as I fill and also check the electronic water level indicator.

I believe I'll start by draining whatever water remains in the tank through the fresh water drain noting how much was left in the tank after the water pump stopped drawing water, just as a reference point.

[JRD]

Only a quart of water or so came out of the fresh water drain, that's good. Tells me that the pump (inlet) take-up is set low enough to draw almost all of the water out of the tank.
I may have to put this project on hold for a few days due to other commitments, but will keep the forum posted.

[JRD]

I added a piece of 1/2 flexible tubing to extend the arch of the vent/overflow 12-13" above the floor. This put the top of the arch above the filler hose inlet. There was enough space under the dinette seat to do it.

After the fix, the tank filled until water began flowing from the filler inlet on the side of the trailer then stopped. During this time, about one gallon of water discharged from the vent/overflow at a moderate rate. This is similar to my old TT in which the vent/overflow hose was connected to the screened vent hole by the filler inlet instead of through the floor and underside.

Before the fix, the tank filled up and immediately gushed about 9-10 gallons of water out the vent/overflow tube, then probably more on the way to a campsite from the water spigot as many have noted on this forum.

I'm sure that installing a valve at the end of the vent/overflow as many have done would also work. I chose this option because I want to maintain the principle of the original system and there is a big caution box in my owners manual regarding closing off the vent tube.

Thanks all for the advice and comments.

JRD