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Old 08-09-2014, 11:24 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
Attached Images
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, 01:59 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, 04:09 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, 05:53 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, 06:12 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, 06:51 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, 09:02 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, 03:04 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, 03:28 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, 03:38 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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Old 08-13-2014, 03:40 AM   #11
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Gotta wonder why they continue to do that if they know it causes issues???
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Old 08-13-2014, 03:43 AM   #12
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yo no sÚ sÚnior
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Old 08-13-2014, 04:21 AM   #13
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My guess is RW ran the white vent hose out the bottom thinking it would be a better solution for the overflow water, rather than in the convenience center. What they did not factor in was the siphoning effect caused by venting that low.
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Old 08-13-2014, 05:50 AM   #14
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Ken,
Precisely! Exactly what I did in the photos.

Thanks for the conformation.

Ken
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Old 08-13-2014, 04:08 PM   #15
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Quote:
Originally Posted by sinder View Post
My guess is RW ran the white vent hose out the bottom thinking it would be a better solution for the overflow water, rather than in the convenience center. What they did not factor in was the siphoning effect caused by venting that low.
Exactly.

It makes sense to me why they didn't run it up to the fill, because the fill is inside a cabinet. My prior RVs had the vent line at the fill, but the fill was always on the exterior of the rig.

I have never had mine siphon out the white vent hose. Luck I guess.
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Old 08-13-2014, 04:49 PM   #16
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To confirm what others have said the white line is supposed to be connected to the vent on the top of the tank. With the valve on the blue "siphon" line under the coach I can now fill the tank completely until it flows out the white line. Subsequently due to the placement of the white line, when water flows out that the tank is absolutely full with little, if any, air in it. It's pretty obvious when you remove the basement wall and look at the fittings on the top of the fresh water tank.
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Old 08-14-2014, 03:53 AM   #17
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They didn't even run our lines thru the belly pan, just stuck them into the belly so if they siphon our belly pan will have water all over inside it.
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Old 08-14-2014, 04:23 PM   #18
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Tom,
Where did you find the line? (the one that is intended to be connect to the convenience center vent) I removed the side of bottom belly pan near convenience center and thought I would see mine there because it's not connected to the vent, but no luck. I didn't have time to look any further as we were getting ready to pull out for a 5 day trip.

Thanks,
Tim
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Old 08-14-2014, 04:40 PM   #19
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Tim, ifyou remove the basement wall you can see the top of the fresh water tank, it is the white hose next to the fill hose. You can follow the fill hose down from the back of the panel to the top of the tank. This is how it is on our 36RE would guess your MB is similar. I haven't pulled the belly pan so don't know for sure where the open end of the blue hose thet others have put the valve on is at. Hope this helps.
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Old 08-14-2014, 04:45 PM   #20
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Tim,
Tom is right. I just pulled the hose straight up and attached it to the vent using a small pipe clamp.

Ken
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