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Old 04-19-2015, 12:46 AM   #29
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Had the siphoning problem on both our Dutch Stars. Solution was to re-route the overfill drain up higher then back down.
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Old 04-19-2015, 09:49 AM   #30
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Reading through these posts shows how lazy and/or ignorant the average RV manufacturer really is.

Pressure fill systems teamed with too-small diameter vents will cause real damage to tanks and hangers and any part of the structure above or below the tank.
Vent pipes pushed down into the tank with outlet below the top of the tank are guaranteed to at least partly empty the tank.
Vent pipes pushed onto spigots welded into the tank and with outlet lower then the top of the tank are guaranteed to start syphoning which collapses the tank and can lose up to 30% of the water.
Vent pipes installed with dips and rises won't function properly either.

etc etc etc

and the builders keep pumping them out with the same faults and owners keep wondering what is wrong with their fresh water tank system.

And then it seems that RV service people and dealers don't read these forums either, otherwise they wouldn't need to mess around finding a solution.
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Old 04-19-2015, 10:04 AM   #31
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A syphon is a simple thing, it happens when the column of water trapped in a hose is longer (and heavier) on the drain side than the other side. It can be stopped by introducing air into the top of the loop, withdrawing the hose from the tank so the hose doesn't allow the column of water to develop, etc.

Just raising the height of the loop will not prevent a syphoning effect, air must be introduced at the top of the loop. (try it with a garden hose)

All of this doesn't answer the Still Bill's question though, how does he gain access to the top of the water tank?
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Old 04-19-2015, 11:26 PM   #32
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fresh water tank

Quote:
Originally Posted by Still Bill View Post
I have a 2013 Itasca Sunstar 30T with the syphoning issue. After completely filling the fresh water tank (or anywhere near it), the action of the water sloshing while driving will make me lose 1/3 to 1/2 tank of water.

Does anyone know how to access the vent hose at the top of the fresh water tank so I can inspect the installation?

Bill

I can access the top of the fresh water tank by removing the metal plate with the exterior shower, pump switches and so in the bay where the sewer drains are. The overflow pipe comes off of the top of the tank on the drivers side front part of the tank. there is about 1 1/4" between the top of the tank and the bottom of the floor, not much room there. I tried to raise the overflow pipe but it never worked for me. looping the longer length of pipe on the top of the tank was the solution for me. Hope this helps you.
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Old 04-19-2015, 11:41 PM   #33
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Quote:
Originally Posted by BFlinn181 View Post


A syphon is a simple thing, it happens when the column of water trapped in a hose is longer (and heavier) on the drain side than the other side. It can be stopped by introducing air into the top of the loop, withdrawing the hose from the tank so the hose doesn't allow the column of water to develop, etc.

Just raising the height of the loop will not prevent a syphoning effect, air must be introduced at the top of the loop. (try it with a garden hose)

All of this doesn't answer the Still Bill's question though, how does he gain access to the top of the water tank?
Actually it does since the water never got up high enough to start the siphon after I raised it.
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Old 04-20-2015, 01:02 AM   #34
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Quote:
Actually it does since the water never got up high enough to start the siphon after I raised it.
Sometimes, or in fact, usually, when the tank is being filled, the signal to turn off the faucet is water running out on the ground from the vent tube. Trouble is, then the syphon has already started and can continue from that point on.

One way to break the syphon is to turn on the outside shower, or the tank drain for a few seconds. However, that won't stop it starting again when you are moving, so raising the loop height will help there.

Don't get too enthusiastic about raising vent outlet levels too high because every 2' means 1psi pressure inside the tank and 1psi over the whole top and bottom area of the tank is a lot of destructive force.
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Old 04-21-2015, 01:05 AM   #35
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I was shown the view behind the fill panel and will come up with a higher loop similar to Winnebago's solution done for ghutch. Still thinking about it. LOL

Thanks all.

Bill
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Old 04-21-2015, 01:11 AM   #36
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Quote:
Originally Posted by Flaco View Post
I can access the top of the fresh water tank by removing the metal plate with the exterior shower, pump switches and so in the bay where the sewer drains are. The overflow pipe comes off of the top of the tank on the drivers side front part of the tank. there is about 1 1/4" between the top of the tank and the bottom of the floor, not much room there. I tried to raise the overflow pipe but it never worked for me. looping the longer length of pipe on the top of the tank was the solution for me. Hope this helps you.
It confirms Gary's solution. Thanks. Bill
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