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Old 08-09-2014, 10:24 PM   #1
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My solution to fresh water syphon

Like many, I installed a valve on the fresh water vent line that sticks through the belly pan. Today, I went to fill the fresh water tank as I'm going to do a dry camp test next week.

When the tank was full, a second vent line, between the hot and cold drains, started to run. It ran for several minutes wasting several gallons of water.

I pulled the basement wall down and found that the top drain was also punched down through the belly pan. Since the hose was lower than the tank and water seeks its own level, naturally it was going to drain until they reached the same level.

I located the unused vent, next to the fresh water fill, pulled the pipe up and attached it using a pipe clamp. I'm not sure what the engineers were thinking. The only downside is that if I overfill, the water will run down into the convenience center and into the garage. A little caulk prevents the water running into the garage and forces the water out the cable/hose cap.

Ken
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File Type: jpg fill and vent.jpg (63.0 KB, 17 views)
File Type: jpg tank fill and over flow.jpg (90.0 KB, 15 views)
File Type: jpg vent unused.jpg (38.0 KB, 15 views)
File Type: jpg overflow attached to vent.jpg (76.8 KB, 15 views)
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Old 08-10-2014, 12:59 PM   #2
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Overfill seeping under the connector panel and into the basement was probably what they were thinking of...
Factory fix is to put a loop in the vent line.
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Old 08-10-2014, 03:09 PM   #3
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Good idea! When I called Redwood, they advised me not to put a valve on the 2nd vent, no explaination given. Nor did suggest a loop on the top vent. Oh well.
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Old 08-10-2014, 04:53 PM   #4
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Those who have installed the valve...leave it open while towing to allow the tank to breath [expand/contract].

Got a good look at the fresh water tank on a rig being built at the factory, there are five ports on the tank...
Fill hose [largest hose on tank, at top corner of FW tank]
Overflow [small white tube located next to fill hose]that exits the coach where the hot/cold low point drains are]
Water pump hose [white hose located at lower rear corner of tank]
Breathing tube??? [blue pex line, comes from the top of the tank, turns down at edge]
Low point drain [blue pex line,located at lower edge of tank, protrudes through the pan under the coach with a valve on it]

The connection that seems to cause people problems is the blue lex line without the valve. I never got a real good answer at to its function but was told to make sure it is open when towing AND while filling.
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Old 08-10-2014, 05:12 PM   #5
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hmmm, wonder why the blue unexplained line starts shooting water well in advance of the other white overflow if they are both out the top?

I do open the valve when filling, but have been closing it when traveling. I suppose I could try to open it, but was afraid it would start running water.

Venting I can certainly understand, these are wide shallow tanks and the tanks flex on top and bottom. The waste tanks have roof vents, but the fresh water does not. I imagine that road travel could certainly cause some action in there that could start damaging things if not allowed to vent. Sounds like instead of the valve, it needs to be elevated or looped. Does the factory understand our issues with it? It starts drain then siphons about 1/3 off the tank before it stops.
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Old 08-10-2014, 05:51 PM   #6
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Fill hose cap left off provides venting too. Makes no sense to me.
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Old 08-10-2014, 08:02 PM   #7
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I talked with Randy the service tech at the RW service center and he indicated that the siphon can happen when the top sags. The factory fix is what we've done placing a valve on the blue line.

At the service center they filled by tank to full with no siphon issue with just the valve on the blue line closed.
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Old 08-13-2014, 02:04 AM   #8
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So quick follow up on my siphon issue. After the service before the rally I decided to test the "siphon" issue that that they couldn't recreate and as the tank filled up in fact water still got siphoned coming out the white hose.

Back in service today for some a/c work and we again addressed it. Turns out that the white hose that comes out under the coach is actually the hose that should get connected to the air vent next to the fill hole. With the hose coming out below the tank a siphon can occur but when its attached to the vent near the fill hole it is above the tank.

Bottom line, with the white hose connected to the vent on top and the blue line closed with the value, no loss of water on a complete fill.

Very happy with the fix now as every camper I've ever used I've always filled the fresh water until it spits out the vent near the fill hole to let me know its full, and now even my RW does that.
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Old 08-13-2014, 02:28 AM   #9
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Ken,

Most Redwoods have that white hose exiting the coach where the hot & cold low point drains are, are you saying they are all done improperly???
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Old 08-13-2014, 02:38 AM   #10
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Well all I can tell you is that there was no hose connected to the vent next to the fill hole. Every RV I've ever used has the fresh water vent connected to the little screened hole next to the fill hole and that is normally where the overflow water comes when I fill it completely up.

Randy in service said RW does run the vent line out the bottom which places it below the tank and therefor can cause a syphon.
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