Need Photos of fresh water tank vent connection

[SouthTX]

In the marine "vented loop", water pressure closes the vent and absence of water pressure allows the vent to open. This allows you to pump fluid through the loop, but breaks the vacuum that could cause a siphon if there is no pumping pressure. This is the same way that the vacuum break on the black tank flush works. The problem is that the vent loop would see "tank slosh pumping" as a pumping pressure that would close the vent and allow the water to be "pumped" out by driving maneuvers.

Rob

I have to disagree with you Rob. IF there was a siphon action, a vented loop like this would break the flow. The sloshing could be mitigated by an elevated loop.

Now, with all that said, this morning I drained my fresh water tank and filled it to overflowing. (59 gallons in a 60 gallon tank). I waited for the overflowing to stop then turned the water on, again. The overflow started immediately - telling me that there was no siphon action continuing to drain the tank. Next time I go out I'll check at my destination to see if I've lost any water from sloshing, but that hasn't been a problem in the past.

Keep in mind that this is a sample size of one 337RLS and its setting level. It is possible that a siphon action might start when hitched up slightly nose high, but this is one way to determine if the problem is due to siphoning or sloshing. Once you know what the problem is, a solution can be crafted - siphon break or elevated loop.

Just thinking out loud - if a problem is found to exist, I wonder if it could be eliminated by attaching a loop to the existing overflow tube that projects through the coroplast? The tops of the tanks appear to be 6 or 8 inches below the floor level so it might be possible to get enough elevation to eliminate the pumping action (or siphoning if that is determined to be the problem). The loop could be attached outboard of the frame in the open area. If more elevation was necessary, there's no reason the line couldn't be extended forward to the basement and put the loop in the basement. That would eliminate dropping the belly and trying to fab a new overflow fitting. Water doesn't sense horizontal distance, only verticle.

Another thought - there is a YT video of cleaning a simulated (clear) black tank with ice. It demonstrates how little sloshing occurs in the black tank so I have to wonder how much occurs in a FW tank.

[DougW9876]

I don't know as the problem is actually siphoning. For a siphon to work the intake end of the hose has to be below the surface of the water. If the vent line is on the side of the tank some siphoning could happen but I don't think you are going to get as much out as some folks are experiencing just through siphoning. Something else is likely going on.

[Harold Graham]

I was told by a Grand Design tech to, fill the tank using the lights on the fresh water gauge, secondly I got conflicting answers from two different techs as to if the fresh water tank is vented to another outside vent other than the overflow hose? One said yes, and another said no. The technician that said it was vented said it was vented through to the roof, is there anybody out there knows if that’s true? I see that there is a round brown vent and round white vent on our 327 RST.
I was wondering if those were vents are for the black and the gray tanks? Also, the over flow pipe must be on the side of the tank for siphoning to occur. The tanks are only 7 inches deep, and span enough distance to where they can be secured between the frame. I would imagine that a slide out could go over the top of the tank, especially if the overflow hose was on the side of the tank.
I no longer carry extra water, as I to use a valve on the overflow tube, knowing that the valve must be open when filling the tank and open when using large amounts of water, like at your campsite.
So far so good and arriving at my destination with a full tank of water instead of a third of a tank water is a good feeling.
Also I must agree with the gentleman who stated that the attitude, nose high, of the fifth wheel could have something to do with the siphoning from the freshwater tank. Note: we have the Nautilus system.

[SouthTX]

I don't know as the problem is actually siphoning. For a siphon to work the intake end of the hose has to be below the surface of the water. If the vent line is on the side of the tank some siphoning could happen but I don't think you are going to get as much out as some folks are experiencing just through siphoning. Something else is likely going on.

I agree, but there have been reports that the overflow tube may be inserted to far or something. This does seem unlikely if they use a bulkhead fitting, but several people have reported less than the rated tank capacity and there have been other reports of the overflow continuing to run and draining a significant amount of water once it starts draining. That's why I wanted to test mine, just to see if there was a siphoning problem and it seems like a good first step for anyone having a problem with water loss. Once you know what the problem isn't, it is easier to find a solution.

[powerscol]

Harold Grham and John - you are both on to something. I have a valve now on the vent line and as correctly stated air still needs to get in on out of the tank to work properly. The tank is under the main floor over the axles. For and air /vac to work properly it must be above the tank. An air/vac works the same as a vented loop allowing air in and out, but not water. MY worry is I will forget to open the valve on the vent line and either over pressurize or collapse the tank. I am beginning to think all I need to do is run the vent line forward to the basement area where I can install the air/vac or vented loop higher than the tank. This could occur above the docking station near the upper floor without having to mess with the tank fittings. I'm guessing that will put the high point of the vent line roughly 2' above the tank and solve the problem of being sure the vent valve is open or closed. The air/vac would also be accessible for maintenance. This will work whether it is siphon or surge flow. When I get my trailer back (waiting on parts), I'll get some measurements done and move forward with the solution. If I am thinking correctly this will be an easy and fairly inexpensive fix no matter which model we have.

Pictures of the vent fitting at the tank would still be appreciated to confirm whether there is another vent on the fresh water tank.

[SouthTX]

Harold Grham and John - you are both on to something. I have a valve now on the vent line and as correctly stated air still needs to get in on out of the tank to work properly. The tank is under the main floor over the axles. For and air /vac to work properly it must be above the tank. An air/vac works the same as a vented loop allowing air in and out, but not water. MY worry is I will forget to open the valve on the vent line and either over pressurize or collapse the tank. I am beginning to think all I need to do is run the vent line forward to the basement area where I can install the air/vac or vented loop higher than the tank. This could occur above the docking station near the upper floor without having to mess with the tank fittings. I'm guessing that will put the high point of the vent line roughly 2' above the tank and solve the problem of being sure the vent valve is open or closed. The air/vac would also be accessible for maintenance. This will work whether it is siphon or surge flow. When I get my trailer back (waiting on parts), I'll get some measurements done and move forward with the solution. If I am thinking correctly this will be an easy and fairly inexpensive fix no matter which model we have.

Pictures of the vent fitting at the tank would still be appreciated to confirm whether there is another vent on the fresh water tank.

I like the way you think - keep it simple.

I was in the hellhole (I cringe when I see all those wires) of my basement the other day and dropped something down the cutout around one of the vent pipes. I was very surprised at how much space there is above the tanks and under the floor. It might be possible to 90 off the existing overflow then another 90 up alongside the frame.

While we're (kind of) on the subject, after I got a good look at the tank arrangement, I think it might be possible to drill a 4 inch hole through the floor over the black tank then a 1 inch hole in the top of the tank and insert a capacitance type probe. Alternatively, it might be possible to access the side of the tank through a hole in the floor to apply the stick-on type sensors to the black tank. Anything is better than fighting the coroplast battle.

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[Txfivver]

~sigh~ all you engineers are keeping me busy lol. I added the shark valve on the water tank vent hose like we were all talking about last month. Now I'm
worried about the tank not venting at all when full and towing. What's the consensus on this now? I will be filling it and towing 200 miles next weekend.

[Cate&Rob]

Harold Grham and John - you are both on to something. I have a valve now on the vent line and as correctly stated air still needs to get in on out of the tank to work properly. The tank is under the main floor over the axles. For and air /vac to work properly it must be above the tank. An air/vac works the same as a vented loop allowing air in and out, but not water. MY worry is I will forget to open the valve on the vent line and either over pressurize or collapse the tank. I am beginning to think all I need to do is run the vent line forward to the basement area where I can install the air/vac or vented loop higher than the tank. This could occur above the docking station near the upper floor without having to mess with the tank fittings. I'm guessing that will put the high point of the vent line roughly 2' above the tank and solve the problem of being sure the vent valve is open or closed. The air/vac would also be accessible for maintenance. This will work whether it is siphon or surge flow. When I get my trailer back (waiting on parts), I'll get some measurements done and move forward with the solution. If I am thinking correctly this will be an easy and fairly inexpensive fix no matter which model we have.

Pictures of the vent fitting at the tank would still be appreciated to confirm whether there is another vent on the fresh water tank.

Keith - I think you are on to something here. Bringing the vent line forward to the water panel area and as high as possible. This would mean that each tank surge "pumping" action would have to supply enough water to fill that extended length of vent hose and lift it to the high point. Ideally, the vent hose extension should have a downward slope all the way back to the tank so that water pumped into it will drain back into the tank. This might be the difficult part to configure. A black tank flush vacuum break could work to vent the high point of the line to make sure a siphon flow can't be started (same as a marine vented loop) . . . but if the line is filled with water being pushed by tank surge, the vent will close and allow the water to pass. This is the same as would happen with tank fill overflow when the tank is completely filled.

Rob

[TucsonJim]

Rob, couldn't you just leave the shut off valve on the bottom of the OEM drain tube that some of us have installed? Then install a tee fitting higher up on the drain tube so that you can run it forward into the panel area. When you're filling the tank, you can open the valve, and run until you see water coming out of the original discharge pipe. Then, close the valve and take your trip. Even if you don't open it right away, there will still be venting at the high point and altitude changes or usage can't hurt anything. When you get to your final destination, you could open the valve which would drain any water that sloshed out and was in the hose.

Like this:



Jim

[klenger]

Lots of great ideas. I think we'll find a fix here.