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Old 05-30-2020, 03:58 PM   #1
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Losing water while driving on the highway

How do you stop water from siphoning from a full water tank ?
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Old 05-30-2020, 04:06 PM   #2
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Put a petcock on it or a ball valve if easily accessible. Just remember to open when set up or you could collapse the tank.
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Old 05-30-2020, 08:21 PM   #3
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Put a petcock on it or a ball valve if easily accessible. Just remember to open when set up or you could collapse the tank.


I did that . Now water comes out of the vent pipe
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Old 05-30-2020, 08:26 PM   #4
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That's where I said to put one. On the vent or if you can access the tank where the vent put one there. The vent goes too deep into the tank and that causes the problem. I moved mine to stop it.
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Old 05-30-2020, 08:35 PM   #5
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Put a petcock on it or a ball valve if easily accessible. Just remember to open when set up or you could collapse the tank.
It is not easily accessible. But if I put a shut off on the vent and leave it closed , will the overflow pipe relieve this pressure ?
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Old 05-30-2020, 08:36 PM   #6
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Should. But I would keep an eye on it just in case.
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Old 05-30-2020, 09:14 PM   #7
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It is not easily accessible. But if I put a shut off on the vent and leave it closed , will the overflow pipe relieve this pressure ?

The 'vent' and 'overflow pipe' are the same 'pipe'. The shut off valve (newly installed?) on the 'vent/over flow pipe' will not allow air flow into the tank if the valve is closed.
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Old 05-30-2020, 09:23 PM   #8
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This happens to me if I fill my fw tank approaching 3/4 full or more and then drive.

99% of the time I carry only slightly more than needed to get to my destination.

Not a boon docker.

Chris
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Old 05-30-2020, 10:00 PM   #9
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How do you stop water from siphoning from a full water tank ?
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Originally Posted by parise View Post
This happens to me if I fill my fw tank approaching 3/4 full or more and then drive.

99% of the time I carry only slightly more than needed to get to my destination.

Not a boon docker.

Chris

Once the suction action starts at the overflow pipe it can go on until the tank is almost empty... The suction action must be 'broken' to stop the flow. Drill a small hole at the top of the tank on the top of the overflow pipe. This will allow air into the pipe and break the suction action. If the tank needs to overflow, no problem, water will run out. If water is not being forced out by too much water, the water will stop flowing because the small hole will allow air into the pipe and 'burp' the over flow pipe system. Once air is in the overflow pipe and it 'burps' there is no more suction within the pipe and water is not able to be pulled out of the tank.
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Old 05-31-2020, 06:44 AM   #10
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We had this issue with our Hemisphere. We had two overflow lines. The solution was to remove the overflow line on the curb side. If that didnt work I was going to loop the remaining overflow so it went above the tank and then to the ground.
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Old 05-31-2020, 01:56 PM   #11
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Once the suction action starts at the overflow pipe it can go on until the tank is almost empty... The suction action must be 'broken' to stop the flow. Drill a small hole at the top of the tank on the top of the overflow pipe. This will allow air into the pipe and break the suction action. If the tank needs to overflow, no problem, water will run out. If water is not being forced out by too much water, the water will stop flowing because the small hole will allow air into the pipe and 'burp' the over flow pipe system. Once air is in the overflow pipe and it 'burps' there is no more suction within the pipe and water is not able to be pulled out of the tank.
I agree that a hole at the top of the overflow pipe will cure the siphoning action but it would be better to install a reducer "tee" at the top of the pipe and attach a separate vent hose that's routed to a higher location and protected from road splash. I believe most overflow/vent pipes (when pipe is used) are 1/2" size. A 1/2-1/14-1/2 "tee" would allow for a 1/4" tube to be routed to a high point.

An open hole in the overflow pipe is a possible entry point for contamination.
To protect the open end of he 1/4" vent tube something simple lile a small engine inline fuel filter could be used. It will let in enough air to break the siphon effect but keep out bugs, dust, etc.
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