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Open Roads Forum  >  Tech Issues

 > fresh water tank overflow syphoning tank dry

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opnspaces

San Diego Ca

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Joined: 12/22/2004

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Posted: 09/11/19 11:50am Link  |  Quote  |  Print  |  Notify Moderator

MURPHY55347 wrote:

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.

The way it appears now the tank is somehow pressurized.


Sounds like Winnebago doesn't understand a siphon. With a siphon it doesn't matter if they run a loop up high if the exit end is lower than the surface of the water. However if Winnebago had taken an extra step to cut or poke a small hole in the tubing at the top of the loop, then a siphon would be impossible. If worried about bugs glue a small piece of mosquito netting over the hole.

Based on your experience at the campground I would say the tank is somehow pressurizing. It would have been interesting to know if the flow would have stopped if you removed the fill cap to relieve any possible pressure.


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1986 Coleman Columbia Popup.

FLY 4 FUN

Alberta

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Posted: 09/12/19 01:41pm Link  |  Quote  |  Print  |  Notify Moderator

I find this thread interesting. Our fifth wheel also has a pressure fill and valves to determine city water/system use/winterize etc. Last year I started noticing that when I fill the tank to capacity it would drain WAY longer than it used to when tap shut off at house. I would get to campsite and notice my "idiot light" was showing 2/3 tank. Not trusting it I ignored it. Now I show up at a campsite and find I can add 1 or 2 6 gallon jerry cans to what I believed was a full tank. In addition our family following us on road trips notes that we lose water on left turns and not just a little...looked like smoke coming off the tires. The last time I topped off the tank I noted water coming out overflow but when I got under the rig there is actually two red "overflow" tubes with one coming out hard/fast and the other trickling out. I wonder why there is two tubes? Is one an overflow and the other the breather tube? I would really like to understand them and may have to pull the coroplast to see whats changed as it used to just drain off a gallon or two as the tank was full and somewhat pressurized.


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Lynnmor

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Posted: 09/12/19 02:31pm Link  |  Quote  |  Print  |  Notify Moderator

FLY 4 FUN wrote:

I find this thread interesting. Our fifth wheel also has a pressure fill and valves to determine city water/system use/winterize etc. Last year I started noticing that when I fill the tank to capacity it would drain WAY longer than it used to when tap shut off at house. I would get to campsite and notice my "idiot light" was showing 2/3 tank. Not trusting it I ignored it. Now I show up at a campsite and find I can add 1 or 2 6 gallon jerry cans to what I believed was a full tank. In addition our family following us on road trips notes that we lose water on left turns and not just a little...looked like smoke coming off the tires. The last time I topped off the tank I noted water coming out overflow but when I got under the rig there is actually two red "overflow" tubes with one coming out hard/fast and the other trickling out. I wonder why there is two tubes? Is one an overflow and the other the breather tube? I would really like to understand them and may have to pull the coroplast to see whats changed as it used to just drain off a gallon or two as the tank was full and somewhat pressurized.


There are two VENT tubes to prevent pressurizing the fresh water tank. With a connection to city water, the incoming pressure can be quite high and the RV manufacturer does not supply a regulator. Two vents give greater capacity for out flowing air and also adds redundancy in case of one becoming restricted. NEVER add valves to these vents, if you ever forget to open them when filling, the tank will expand causing considerable damage. If you pump water from an unvented tank it will collapse and possibly dislodge from the supports. If your check valve in the water pump or the fill valve leaks, that too will fill the tank when connected to city water so the vents need to work always.

The fact that you didn't see the water spilling out in the past was just a matter of chance, straight roads cause less spilling.

The answer is to run the vents up and out of the coach well above the water level.

I added a gravity fill port of the hatch type. The elbows at the top are the required vents. The small holes in the door act as an insect screen and allows venting with the door closed and locked. The fill hose was attached to the tank by spin welding a hose barb to it.

[image]





Lantley

Ellicott City, Maryland

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Posted: 09/12/19 04:18pm Link  |  Quote  |  Print  |  Notify Moderator

Lynnmor wrote:

FLY 4 FUN wrote:

I find this thread interesting. Our fifth wheel also has a pressure fill and valves to determine city water/system use/winterize etc. Last year I started noticing that when I fill the tank to capacity it would drain WAY longer than it used to when tap shut off at house. I would get to campsite and notice my "idiot light" was showing 2/3 tank. Not trusting it I ignored it. Now I show up at a campsite and find I can add 1 or 2 6 gallon jerry cans to what I believed was a full tank. In addition our family following us on road trips notes that we lose water on left turns and not just a little...looked like smoke coming off the tires. The last time I topped off the tank I noted water coming out overflow but when I got under the rig there is actually two red "overflow" tubes with one coming out hard/fast and the other trickling out. I wonder why there is two tubes? Is one an overflow and the other the breather tube? I would really like to understand them and may have to pull the coroplast to see whats changed as it used to just drain off a gallon or two as the tank was full and somewhat pressurized.


There are two VENT tubes to prevent pressurizing the fresh water tank. With a connection to city water, the incoming pressure can be quite high and the RV manufacturer does not supply a regulator. Two vents give greater capacity for out flowing air and also adds redundancy in case of one becoming restricted. NEVER add valves to these vents, if you ever forget to open them when filling, the tank will expand causing considerable damage. If you pump water from an unvented tank it will collapse and possibly dislodge from the supports. If your check valve in the water pump or the fill valve leaks, that too will fill the tank when connected to city water so the vents need to work always.

The fact that you didn't see the water spilling out in the past was just a matter of chance, straight roads cause less spilling.

The answer is to run the vents up and out of the coach well above the water level.

I added a gravity fill port of the hatch type. The elbows at the top are the required vents. The small holes in the door act as an insect screen and allows venting with the door closed and locked. The fill hose was attached to the tank by spin welding a hose barb to it.

[image]

I don't disagree that running the vents up and out is a good solution. However accessing the tanks to accomplish this is not a simple task.
Putting on valves is very easy. Tie a string to your faucet/finger or whatever it takes to remember to open the valves!


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