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Alta Sierra · 07-03-2014, 12:11 PM

Hello! I dealt with this problem back in late 2012, and I thought that I had it solved. Nope...it has 'reared its ugly head again!

The problem: the fresh water tank on this motor home lies on top of the frame rails and is rectangular in shape with its height being only about 7". Just above the tank is the underside of the motor home's floor.

The overflow/vent line begins with a 1/2" NPT 90-degree elbow at the top of the tank , which connects to a short piece of 1/2" PEX tube, a 90-degree PEX elbow and then drops down through the floor of the compartment , terminating with a 'bug screen' just below the compartment's floor to the road surface.

I was losing a lot of my fresh water from the tank when driving down the road, especially when making right turns. In addition, if I filled the tank all the way up, about one-third of the water would immediately siphon out of the tank, through the overflow/vent line.

I cut in a 1/2" brass check valve just downstream from the elbow at the top of the tank, and then looped 4' of tubing from there over the top of the tank, bringing the end of that tubing back over the tubing that exits the elbow at the top of the tank. The another 90-degree elbow continued the line down through the lower compartment and through the floor.

Prior to installing the swing-type check valve, I tested it to make sure that it would still allow air to vent in its static (unloaded) position. The system seemed to work fine for the first year. In October of 2013, I was filling the tank before leaving Jackson, WY, and I heard a 'pop'... I immediately shut off the incoming water. The top of the tank had stretched (due to trapped air) and was up against the floor of the motorhome. Obviously there was an issue with the check valve. which I just removed (yesterday).

As I removed the check valve yesterday, I heard air pressure escaping from the tank as I loosened the union nut on the upstream side of the check valve.

I have been on the Internet this morning, trying to find a solution to this obvious manufacturer's design error. The only thing that seems to have worked is to re-install the 4-foot loop of tubing on top of the tank, and secure it where it crosses above the line exiting the fitting at the top of the tank. From there, connect a 90-degree elbow (pointing down), and add short piece of tubing (and attach the 'bug screen there) terminating into a 1-1/2"PVC 'dry standpipe' that will direct any vented water down though the bottom of the compartment's floor. The dry standpipe will be slotted at it's top to accept and cradle the tubing and fitting near the top of the tank, allowing the standpipe to sit flush against the inside of the 'roof' of the compartment.

By raising the bottom of the overflow/vent line to very near the top of the tank, that should greatly decrease the siphoning, especially if I drill a 1/8" hole into the top portion 90-degree elbow as a vacuum breaker.

I would appreciate anyone's thoughts on this before I perform the modifications.

mel s · 07-03-2014, 02:19 PM

Quote:

Originally Posted by Alta Sierra

Hello! I dealt with this problem back in late 2012, and I thought that I had it solved. Nope...it has 'reared its ugly head again!

The problem: the fresh water tank on this motor home lies on top of the frame rails and is rectangular in shape with its height being only about 7". Just above the tank is the underside of the motor home's floor.

The overflow/vent line begins with a 1/2" NPT 90-degree elbow at the top of the tank , which connects to a short piece of 1/2" PEX tube, a 90-degree PEX elbow and then drops down through the floor of the compartment , terminating with a 'bug screen' just below the compartment's floor to the road surface.

I was losing a lot of my fresh water from the tank when driving down the road, especially when making right turns. In addition, if I filled the tank all the way up, about one-third of the water would immediately siphon out of the tank, through the overflow/vent line.

I cut in a 1/2" brass check valve just downstream from the elbow at the top of the tank, and then looped 4' of tubing from there over the top of the tank, bringing the end of that tubing back over the tubing that exits the elbow at the top of the tank. The another 90-degree elbow continued the line down through the lower compartment and through the floor.

Prior to installing the swing-type check valve, I tested it to make sure that it would still allow air to vent in its static (unloaded) position. The system seemed to work fine for the first year. In October of 2013, I was filling the tank before leaving Jackson, WY, and I heard a 'pop'... I immediately shut off the incoming water. The top of the tank had stretched (due to trapped air) and was up against the floor of the motorhome. Obviously there was an issue with the check valve. which I just removed (yesterday).

As I removed the check valve yesterday, I heard air pressure escaping from the tank as I loosened the union nut on the upstream side of the check valve.

I have been on the Internet this morning, trying to find a solution to this obvious manufacturer's design error. The only thing that seems to have worked is to re-install the 4-foot loop of tubing on top of the tank, and secure it where it crosses above the line exiting the fitting at the top of the tank. From there, connect a 90-degree elbow (pointing down), and add short piece of tubing (and attach the 'bug screen there) terminating into a 1-1/2"PVC 'dry standpipe' that will direct any vented water down though the bottom of the compartment's floor. The dry standpipe will be slotted at it's top to accept and cradle the tubing and fitting near the top of the tank, allowing the standpipe to sit flush against the inside of the 'roof' of the compartment.

By raising the bottom of the overflow/vent line to very near the top of the tank, that should greatly decrease the siphoning, especially if I drill a 1/8" hole into the top portion 90-degree elbow as a vacuum breaker.

I would appreciate anyone's thoughts on this before I perform the modifications.

Alta Sierra
My only comment is that that vent line/hose, (on my coach), is a "2 way vent".
It serves 2 purposes:
1st to allow air OUT/escape when filling the tank with pressurized city/campground.
2nd to allow "makeup air" IN when water is being drawn out of the tank by the water pump.
Most, (all?), plastic RV water tanks are neither a pressure or a vacuum vessel........ undo tank flexing will evenualy result in tank failure.
A check valve, (or a shut off valve), in the vent line/hose....can/will cause tank flex.....either outward when filling...or inward when using water via the 12V pump.
Mel
'96 Safari

zman-az · 07-05-2014, 10:12 AM

Does that vent line come out the side at the top of your tank or actually on the top? I have delt with this on my vista and fixed the design flaw. Mine vent was on the side of the tank at the top and suspect that is where yours is too.

corjaguar · 07-05-2014, 11:27 AM

On our trip now in progress, I must have overfilled the fresh water tank.....I heard a pop and looked to see what it was, I found a slender filter looking object on the ground and water funning out. I couldn't figure out if this slender filter object was inside the tube hanging down through a hole or what.....I decided to just find something to be inserted inside this white flex hose and clamped it tight.
I checked a couple of RV repair facilities and they couldn't identify the slender filter like object.

I was wondering if it should just be reinserted back into the hose and hope the water doesn't run out

mel s · 07-05-2014, 11:46 AM

Quote:

Originally Posted by corjaguar

On our trip now in progress, I must have overfilled the fresh water tank.....I heard a pop and looked to see what it was, I found a slender filter looking object on the ground and water funning out. I couldn't figure out if this slender filter object was inside the tube hanging down through a hole or what.....I decided to just find something to be inserted inside this white flex hose and clamped it tight.
I checked a couple of RV repair facilities and they couldn't identify the slender filter like object.
I was wondering if it should just be reinserted back into the hose and hope the water doesn't run out

corjaguar
Can you post a pic of the "slender filter like object"?
Mel
'96 Safari

corjaguar · 07-05-2014, 05:30 PM

I don't know how to send a photo from this forum....I could send you and email picture.......

Alta Sierra · 07-06-2014, 09:48 PM

Corjaugar: That slender filter -like object is a bug filter that connects to the bottom of the vent line, below the compartment. It is there to prevent insects from entering the line and continuing on into the water tank in search of a water source.

The overflow/vent outlet on my 2011 Itasca's water tank is at the top, very near to the corner...not on the side wall of the tank at all. The fitting is a 1'2" NPT double-male threaded 90-degree fitting that is threaded vertically into the tank, and exits with a horizontal 1/2" NPT male pipe thread.

I am still working on a solution to the siphoning issue.. and I think that I may have a solution figured out. I will post more information as I progress.

Itasca's engineers should be ashamed of themselves for designing such a problematic system.

Regards, Alta Sierra

mdpuff · 07-06-2014, 10:08 PM

I had the same problem with our old motor coach, fill the tank then drive to our destination to find I lost around a 1/4 tank of water. My solution was to put a simple ball valve in the overflow / vent tube that I would close after I filled the tank then open when reaching our destination. Worked great as long as you don't forget to open the valve when necessary. Used this system for 10 years without an issue.

charles tuit · 07-07-2014, 07:25 AM

After filling the water tank and before leaving run the outside shower hose for about 30 seconds. This breaks the vacuum caused from filling. Works for me.

bchcmpr · 07-07-2014, 10:23 AM

i had same problem with my 05 siteseerer i did the the same thing as mdpuff put a ball valve in the over flo line i only fill my tank with the gravty fill not the city water fill witch is pressurized good luck

zman-az · 07-10-2014, 07:59 PM

Alta Sierra,

Here is what was going on with my 2011 Vista with the side tank exit. When you fill the tank the tank expands from the weight of the water. When you top it off water comes out the overflow tube. This causes a siphon effect and it will continue to siphon the water out of the tank, air cannot get in the overflow tube to stop the siphon so it continues and the tank start to concave. At some point when it can no longer concave it then pulls in some air in from the overflow tube and the process stops. Because the tank concaves when air is drawn back in the tank will flex back out and that is why mine was almost 1/3 empty. To fix this I put a tee at the outlet of the tank (which also is the highest point of the overflow tube) and ran a tube about 6" higher than the tank to stop the siphoning and still retained the overflow tube. I used pex push on fittings to make the install easy. Watts makes a plastic version similar to the sharkbite fittings but cheaper.

I am wondering if the fitting on your tank sits a 1" or 2 inside the tank, if so you may be seeing the same thing I went thru. You could always fill your tank until it comes out the overflow tube and then watch to see if the process occurs. If you have access to the side and middle of the tank you might even be able to measure the expansion/contraction.

jcullipher · 07-10-2014, 09:37 PM

Following this as I have a 2013 Thor Challenger with the same issue. I will sometimes lose half tank of fresh water.

tderonne · 07-10-2014, 10:00 PM

My fix:

About $2.00 at Lowes. I was able to reuse the critter screen from the end of the old line inside the elbow. Did a test fill where I filled it (via the gravity fill) until water came out the overflow. About 2 quarts drained into a bucket and it stopped. If I did that before it would have drained more like 5 gallons. I consider it fixed.

1/2" PEX to 1/2" pipe adapter (yes should be a crimp ring on there, hose clamp in this non-pressurized fitting is fine) into a 1/2" pipe to 1 1/2" bushing, into 1 1/2" PVC elbow and pipe. If that isn't obvious. Had to drill a larger hole in the floor, simple in mine.

Alta Sierra · 07-11-2014, 09:08 AM

Hello,

My Thanks to everyone who has responded do far.

The siphoning issue is the minor problem... and that may be able to be prevented by filling the water tank only 3/4 full before 'hitting the road'.

The main issue is that after I fill the tank and hit the road, I lose a lot of water (from sloshing) out of the overflow/vent tube whenever I make right-hand turn, or stop at a red light/stop sign. That 'sloshing-loss' stops happening after I lose about half of the water from the tank. The overflow/vent line 90-degree fitting is near the front corner of the tank, on the driver's side of the coach.

With the water tank 1/2 full, there is only three inches of space from the top of the tank to the underside of the motorhome's floor. The 90-degree fitting takes up about 1-1/2 inches of that space. When the water tank reaches the top of the tank (at the sides of the tank), an air pocket (bubble) begins to develop in the center of the tank, far away from the overflow/vent fitting. As designed by Itasca, there is no way to 'gravity-fill' the water tank on this motorhome. Itasca built it with only with a city water pressure-fill connection for the fresh water tank.