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Open Roads Forum  >  Tech Issues

 > fresh water tank overflow syphoning tank dry

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Goostoff

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Posted: 09/05/19 10:05pm Link  |  Quote  |  Print  |  Notify Moderator

Let me start by stating that my overflow in a tube sticking out the bottom of the underbelly of the trailer. I have always just filled my tank untill water starts to flow out of the tube. It would always drain off the little bit that got in before I could pull the hose. For some odd reason this year when i do this the water will sit there and keep running out and will syphon the tank nearly dry before it stops running. Anyone have any idea what is going on. I'm thinking about installing a valve on the end but I fear that I would forget to open it and make even more problems


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EV2

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Posted: 09/05/19 10:22pm Link  |  Quote  |  Print  |  Notify Moderator

It can only siphon to the level of the opening inside of the tank. It sounds as though the tube is no longer at the top of the tank, but is now at the bottom.

shoprma

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Posted: 09/06/19 03:55am Link  |  Quote  |  Print  |  Notify Moderator

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Lantley

Ellicott City, Maryland

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Posted: 09/06/19 04:47am Link  |  Quote  |  Print  |  Notify Moderator

I have the same issue and I have valves on the ends of my vent and overflow pipes.
Yes you must remember to open valves.
Just make opening valves part of your setup routine


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DutchmenSport

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Posted: 09/06/19 07:01am Link  |  Quote  |  Print  |  Notify Moderator

Normally, isn't the overflow pipe also the vent pipe? If you close off the vent pipe with a valve, wouldn't that cause a vacuum in the tank and then nothing would pump out with the on-board pump.

Most tanks have a drain valve and an over-flow/vent. The end of the over-flow/vent is usually placed higher than the top of the tank, and installed in such a way that the direction is always upward, never down. Down could cause a vacuum in the tank.

Even if your tank is siphoning, there has to be a secondary opening somewhere to prevent the tank from vacuuming up, unless when you disconnect the water hose and the air is coming from there. Now, if you fill is gravity fill, then it does have the secondary opening to allow siphoning to occur.

So, I guess what I'm asking, are you sure that tube UNDER the trailer is not the drain valve and the vent is somewhere else? I've never heard of having the vent tube 'below' the object it's venting, only above it.

drsteve

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Posted: 09/06/19 07:27am Link  |  Quote  |  Print  |  Notify Moderator

DutchmenSport wrote:

Normally, isn't the overflow pipe also the vent pipe? If you close off the vent pipe with a valve, wouldn't that cause a vacuum in the tank and then nothing would pump out with the on-board pump.

Most tanks have a drain valve and an over-flow/vent. The end of the over-flow/vent is usually placed higher than the top of the tank, and installed in such a way that the direction is always upward, never down. Down could cause a vacuum in the tank.

Even if your tank is siphoning, there has to be a secondary opening somewhere to prevent the tank from vacuuming up, unless when you disconnect the water hose and the air is coming from there. Now, if you fill is gravity fill, then it does have the secondary opening to allow siphoning to occur.

So, I guess what I'm asking, are you sure that tube UNDER the trailer is not the drain valve and the vent is somewhere else? I've never heard of having the vent tube 'below' the object it's venting, only above it.


What he said.


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Bobbo

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Posted: 09/06/19 07:50am Link  |  Quote  |  Print  |  Notify Moderator

Goostoff wrote:

Let me start by stating that my overflow in a tube sticking out the bottom of the underbelly of the trailer.

I have never seen an overflow (actually vent) tube anywhere except right beside the gravity fill port. If you have a fancy trailer with levers to flip rather than a gravity fill port, I have no idea.


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Posted: 09/06/19 07:54am Link  |  Quote  |  Print  |  Notify Moderator

drsteve wrote:

DutchmenSport wrote:



So, I guess what I'm asking, are you sure that tube UNDER the trailer is not the drain valve and the vent is somewhere else? I've never heard of having the vent tube 'below' the object it's venting, only above it.


What he said.


What they said





Lynnmor

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Posted: 09/06/19 08:02am Link  |  Quote  |  Print  |  Notify Moderator

Do you have a gravity fill where you just stick in a garden hose? Does it have a vent next to it? Are you sure that the pipe expelling water is a vent? Is the trailer sitting level? Do you have a means of pressure filling the tank with a garden hose attached?





Lynnmor

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Posted: 09/06/19 08:06am Link  |  Quote  |  Print  |  Notify Moderator

DutchmenSport wrote:



So, I guess what I'm asking, are you sure that tube UNDER the trailer is not the drain valve and the vent is somewhere else? I've never heard of having the vent tube 'below' the object it's venting, only above it.


Tens of thousands of RVs were/are produced with a pipe attached to the top corner of the water tank and then run out thru the bottom. No, they don't work, it is just a cheap way to get them out the door.

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