Vent System and Overflow Valve to Prevent Water Loss

[Guest]

I finally have gotten around to finish up the vent system with overflow in hopes of preventing water loss due to sloshing. First I wanted a locking water gravity fill so that was installed a couple months ago. An adapter had to be used since anything coming in from across the pond is not standardized. In this case the gravity fill is 1 1/2 inch and the fill line is 1 3/8. Go figure.

The modified overflow has been in place for a couple years. Yes things move slow it seems.

The modified overflow with ball valve has been tee'd into an overflow that connects to the gravity fill. I have no issue closing the ball valve during travel, but forgetting to open it once we are camping could be devastating to the tank due to collapse. The vent will prevent that issue. So consider this an old age tank damage preventive device.

I will be testing this tomorrow to see how much water is lost since I expect some may slosh out of the small vent line. This can be improved by extending the vent as far under the kitchen cabinet as possible, and back down to the gravity fill. Since the drawer slides are like razor blades, I decided to take the easy route as an initial test and connected it directly.

Jim

[Guest]

Update: After a 60 mile run with 15 in city traffic, I've lost no water through the vent line. It figures since the vent line is 3/8" and terminated at the gravity fill through a 1/4" hole and my tank was full so sloshing cannot really happen through an opening this small and with the overflow lines full of water with ball valve closed. The side of the rig was dry when I arrived.

I put a piece of paper towel close to the vent and it was wet once I arrived where only enough water was able to escape to make it wet. Near nothing.

For those that travel with 10 gallons or so, nothing is needed. For those that want to haul a full tank and not be concerned about forgetting to open the overflow ball valve and damaging their tank, this works.

Ideally the vent could have been looped up to the very top drawer support under the kitchen counter and back down to the gravity fill, but I will not be making any changes.

Having forgotten to open my overflow ball valve one time after about 6 gallons of use, I knew I needed to make this change since it only takes once to really damage the tank with significant usage and no venting.

So why does GDRV not use the vent and get rid of the overflow line? To prevent over pressuring the tank most likely when filling. Filling with a water hose could overwhelm the small vent at the gravity fill and damage the tank. The original overflow without the ball valve prevents damage but will allow 1/3 of your water to disappear over the road due to sloshing without a modification. This method prevents sloshing as well as damage with a dedicated vent.

Jim

[TedS]

As long as the vent end is above the tank there will be little to no water coming out.

Nice job. I agree, gdrv should do something similar and forget the overflow.

[Cate&Rob]

The problem is that many Grand Design products do not have a gravity fill provision for the fresh water tank . . . and the included vent connection.

The twin vent/overflow design has been implemented on most models https://gdrvowners.com/forum/operati...problem-solved and has solved the siphon action that was being initiated by sloshing. Some amount of water can still slosh out but this is very minor compared to the siphon problem.

Rob

[Guest]

Rob,

Your twin tube idea is a great solution to inexpensively stop the siphon action. But slosh will still take place unless the overflow location at the tank is changed. Running the clear line down along side the tank from the gravity fill to the overflow line below the rig was much easier than I originally thought it would be. And it solves all issues for me. Siphon by closing the ball valve after filling, and no water loss while traveling. And no damage to the tank if I forget to open the ball valve. Not a perfect solution since the real issue is currently not allowing air to enter the top/mid section of the tank.

Mdot in = Mdot out in engineering gobbldy goop.

If a larger vent was used on all models and placed on the side of the rig and above the top of the tank, I believe all issues would be solved with respect to siphon, overpressure or collapse. Below is such a vent used on marine fresh water and fuel tanks.

https://www.westmarine.com/buy/perko...l-vent--281360

Jim

[TedS]

The problem could have also been solved with a single vent line run uphill and terminating above the fresh water tank. And no overflow loss.

[Jlawles2]

On the 303 which is a similar floor plan as my last 5er, there is enough room to put a gravity fill or vent line at the street side rear of the unit. This will require punching through the floor and using the space behind the receptacle for a wall penetration. On my pervious 5er, the gravity fill for the tank and power inlet location was in this area. they could even shorten the depth of the cabinet if needed for extra room.

[ncitro]

The problem could have also been solved with a single vent line run uphill and terminating above the fresh water tank. And no overflow loss.

Thats what I did with mine. Ran it up and onto the rear wall of the rig. None lost from sloshing or siphon.

[Guest]

Wherever you run the vent, it must be higher than the tank and able to drain back into the tank or looped high to drain both ways to avoid water sitting in the line.

Jim