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Open Roads Forum  >  Tech Issues

 > fresh water tank overflow syphoning tank dry

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Lynnmor

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Posted: 09/09/19 08:11am Link  |  Quote  |  Print  |  Notify Moderator

Lantley wrote:

Lynnmor wrote:

I have been thru this too many times before. The reason that things never change is that too many have no idea how things work.


Is it up to the buyer to understand how to correctly pipe a fresh tank?
Do I need to submit my own drawings at time of purchase?


Unfortunately that is the case. The manufacturers will take the least expensive route every time. Tens of thousands of RVs have been produced with this flawed design and precious few owners have a clue.

Here is my original tank, the blue pipes are the vents (cut short) where the water sloshes out.

[image]





steved28

Bellingham,MA,USA

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Posted: 09/10/19 12:13pm Link  |  Quote  |  Print  |  Notify Moderator

Lantley wrote:

My set up does not gravity fill. You can fill via a pressurized water hose or via a bucket using the on board pump. Filling is not a problem. I have a 80 gallon fresh tank,filling via gravity would be a PIA.
My overflow and vent tube both exit beneath the fresh tank.If you overfill the fresh tank a siphon will/can start. Once started the siphon can dump a lot of water on the ground.
iIhave resolved this issue by installing valves on my drain and siphon lines


This doesn't make any sense. If it allows a siphon, no matter how, it is no longer a vent, it is now a drain. Any vent should be above the water level, regardless of where the vent pipe may lead after that. Who on Earth would put a vent below the waterline???


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maillemaker

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Posted: 09/10/19 12:21pm Link  |  Quote  |  Print  |  Notify Moderator

Water might slosh out of a top-plumbed, bottom-drain vent line, but it's not going to siphon.

Once the water level is below the mouth of the vent tube, it cannot siphon.


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Lantley

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Posted: 09/10/19 04:26pm Link  |  Quote  |  Print  |  Notify Moderator

I guarantee you it's a siphon. As I said the water will continue to flow long after I disconnect the fresh tank fill hose. All it takes is for the vent or drain hose to fall into the tank a bit and a siphon is possible!
Granted the entire system could have been designed and constructed better but this is the RV world where proper design and construction is low on the priority list.


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drsteve

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Posted: 09/10/19 07:40pm Link  |  Quote  |  Print  |  Notify Moderator

Lantley wrote:

...this is the RV world where proper design and construction is low on the priority list.


Which is behind many if not most RV related problems.


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MURPHY55347

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Posted: 09/10/19 09:02pm Link  |  Quote  |  Print  |  Notify Moderator

So we have a Winnebago Motorhome purchased last year. Worked great all last year and most of this. My normal routine is to fill fresh water tank till it flows out the vent. It will run out for a bit then stop. Drive to campground and all is fine. Now get to campground back into my spot and water is running out the overflow. How can this be? There is no tube in the tank, just a 90 degree fitting off the top of the tank, a 4” piece of hose that goes horizontal to the tank and another 90 degree fitting with a hose going down under the coach. How can siphoning occur without a hose in the tank? Even if siphoning did start once water sloshed to the other side of the tank the vacuum would be broken. Was at the Winnebago factory yesterday and today and guess what. They don’t understand it either. Yesterday they put a loop of tubing in the vent line that went above the tank then down. Gave me the coach back and said all would be good. No way it could siphon with a loop above the tank. Nope! 70 miles down the road stopping at a wayside got out to look and sure enough it is running out the overflow. Turned around and went back. Today the change the angle of the 4” piece of tubing and raised it about an inch. Drove home and it appears to have worked. Will want to test more before any cheering. What I am still questioning is what part the gravity fill port might have to do with this. Never had one before this one. If that lets air in and siphoning starts it could contribute to the problem. If no gravity fill port, no air could get into the system and eventually there would be negative pressure in the tank stopping any siphoning. The way it appears now the tank is somehow pressurized.

Lynnmor

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Posted: 09/11/19 07:04am Link  |  Quote  |  Print  |  Notify Moderator

MURPHY55347 wrote:


Today the change the angle of the 4” piece of tubing and raised it about an inch. Drove home and it appears to have worked. Will want to test more before any cheering. What I am still questioning is what part the gravity fill port might have to do with this.


The spill will continue till the water level drops to the vent port. Running the vent up hill by 1" will reduce spillage a bit. If the trailer leans to the side where the vent is connected, the spill will start, if leaning the opposite way there will be no spill.

A gravity fill system has a vent and fill pipe well above water level and that is why they work. A pressure fill system needs to have vents well above water level, but that would cost a few dollars that the manufacturers will not spend.

The manufacturer that I fought with changed back to gravity fill to fix the problem, but they still have no clue why water only runs downhill.

If you think that your problem is fixed, have a car follow close behind on a curvy mountain road so they can record the spillage. Yes, I did that.

Lantley

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Posted: 09/11/19 07:19am Link  |  Quote  |  Print  |  Notify Moderator

Lynnmor wrote:

MURPHY55347 wrote:


Today the change the angle of the 4” piece of tubing and raised it about an inch. Drove home and it appears to have worked. Will want to test more before any cheering. What I am still questioning is what part the gravity fill port might have to do with this.


The spill will continue till the water level drops to the vent port. Running the vent up hill by 1" will reduce spillage a bit. If the trailer leans to the side where the vent is connected, the spill will start, if leaning the opposite way there will be no spill.

A gravity fill system has a vent and fill pipe well above water level and that is why they work. A pressure fill system needs to have vents well above water level, but that would cost a few dollars that the manufacturers will not spend.

The manufacturer that I fought with changed back to gravity fill to fix the problem, but they still have no clue why water only runs downhill.

If you think that your problem is fixed, have a car follow close behind on a curvy mountain road so they can record the spillage. Yes, I did that.

I feel your pain. However I did not try to figure out what was causing the siphon. I really have no desire to remove the underbelly to get to the root of the problem. I am not located near the factory.
I simply put shark bite valves on the vent and overflow lines to stop the water loss. Yes I have to remember to open the lines when I get to the CG. Kind of a crude solution but it works for me.

steved28

Bellingham,MA,USA

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Posted: 09/11/19 07:28am Link  |  Quote  |  Print  |  Notify Moderator

MURPHY55347 wrote:

So we have a Winnebago Motorhome purchased last year. (snip)


I was surprised to hear it was a Winnebago. As they are one of the few manufacturers who actually fabricate their own tanks, specific to the model of the RV. I'm curious to hear what you have, since I purchased a new class A from them last year. I still think the only logical explanation of a siphon would be if the drain/overflow pipe somehow dropped into the tank, or was not installed correctly to begin with, and sits under the water level in the tank.

BTW, I have both a gravity and a pressure feed to fill the tank.No issues here (yet)

MURPHY55347

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Posted: 09/11/19 08:47am Link  |  Quote  |  Print  |  Notify Moderator

We have a Vista LX 27N. Winnebago assures me there is no pipe on the vent that extends into the tank. If you look at their plumbing diagrams you will see that on the overfill pipe the use 1/2” tubing. Then to prevent siphoning they slip a larger diameter pipe over this and attach it with a screw. The theory is that the space created between these 2 different diameter pipes is supposed to let air in to prevent siphoning. Seems to be hit and miss wether it works or not.

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