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Old 12-02-2021, 07:35 AM   #1
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Water dumps when filling fresh tank

Like many of you I my 07 National Pacifica uses this panel for water control. I put the lever to fill the fresh water tank and begin to fill it. If I allow it to go past about 3/4 full, it begins to dump the tank. I cannot stop this dump by controlling any of the levers and then when the tank is EMPTY it stops and I can begin to fill.

What is going on????
What can I do to completely fill the tank and stop the overflow drain?
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Old 12-02-2021, 08:14 AM   #2
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Is the 3/4 mark actually the full level of the tank? Sounds like it starts overflowing thru the vent line when it reaches that level. Can you see where the water is dumping out from the tank and/or the level of the fill/vent line into tank?
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Old 12-02-2021, 10:24 AM   #3
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Is the 3/4 mark actually the full level of the tank? Sounds like it starts overflowing thru the vent line when it reaches that level. Can you see where the water is dumping out from the tank and/or the level of the fill/vent line into tank?
This^^, is your starting point.

Unless you visually see the water level of the tank, the level gauges inside the coach should not be trusted. I suspect your tank is full when the gauge reads 3/4 full.

An overflow vent/line should not siphon water down to a low level in the tank as the vent is usually connected to the top and does not have a hose extended into the water. If you are actually losing all the water and the flow does not stop until the tank is empty, the siphon is from another line that is connected to the system or tank and you need to hunt down exactly from where the water is flowing. Once you find the source, you can either cap the end, or trace the line to find why it is siphoning from the fresh tank.

Here's one possible suspect, the winterizing valve and line. The winterizing line is tapped into the line that exits the tank, near the bottom, and just before the pump. That line, which is used to draw in antifreeze, could be routed upward toward the top of the tank before it exits near the access area by the water bay. Filling the tank will fill that line, and if the winterizing valve is OPEN, the line will fill and eventually a siphon will be created drawing the water out.

Once again, it is important to find exactly where the water is exiting.
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Old 12-02-2021, 10:31 AM   #4
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Originally Posted by SC182 View Post
Is the 3/4 mark actually the full level of the tank? Sounds like it starts overflowing thru the vent line when it reaches that level. Can you see where the water is dumping out from the tank and/or the level of the fill/vent line into tank?
This^^, is your starting point.

Unless you visually see the water level of the tank, the level gauges inside the coach should not be trusted. I suspect your tank is full when the gauge reads 3/4 full.

An overflow vent/line should not siphon water down to a low level in the tank as the vent is usually connected to the top and does not have a hose extended into the water. If you are actually losing all the water and the flow does not stop until the tank is empty, the siphon is from another line that is connected to the system and you need to hunt down exactly from where the water is flowing. Once you find the source, you can either cap the end, or trace the line to find why it is siphoning from the fresh tank.
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Old 12-02-2021, 12:05 PM   #5
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Originally Posted by PacificaDen View Post
Like many of you I my 07 National Pacifica uses this panel for water control. I put the lever to fill the fresh water tank and begin to fill it. If I allow it to go past about 3/4 full, it begins to dump the tank. I cannot stop this dump by controlling any of the levers and then when the tank is EMPTY it stops and I can begin to fill.

What is going on????
What can I do to completely fill the tank and stop the overflow drain?
What you're experiencing is the overflow mechanism. It's designed to extract a given amount. Once it sees or, the amount in the tank exceeds a safe amount, the overflow takes over. And, once it starts flowing, you have ZERO ability to stop the flow, until the level is below the point that the overflow pick-up, will not pick up any more water. It's no big deal.

I trust my water level gauges explicitly. They work flawlessly in telling me the levels, in ALL my tanks.
Scott
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Old 12-02-2021, 04:45 PM   #6
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What you're experiencing is the overflow mechanism. It's designed to extract a given amount. Once it sees or, the amount in the tank exceeds a safe amount, the overflow takes over. And, once it starts flowing, you have ZERO ability to stop the flow, until the level is below the point that the overflow pick-up, will not pick up any more water. It's no big deal.

I trust my water level gauges explicitly. They work flawlessly in telling me the levels, in ALL my tanks.
Scott
If the post from the OP is accurate, he is losing all the water in his tank. I donít believe any overflow mechanism is designed to drain all the contents once the overflow is triggered.

One suspect is the winterizing valve and hose. They tap into the line from the bottom of the tank, just before the pump. If the valve is open and the hose is routed upward to about the 3/4 tank level before it drops down to the wet bay, filling the tank will fill the hose until a siphon is created. It will continue until the water empties the tank.

We need to know exactly from where the water is draining, and if the OP can operate his system just using the pump.
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Old 12-02-2021, 07:59 PM   #7
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If the post from the OP is accurate, he is losing all the water in his tank. I donít believe any overflow mechanism is designed to drain all the contents once the overflow is triggered.
Itís the siphon effect. Happens in my coach too. Once the overflow starts, thereís no stopping it until the water tank is empty.

Unless you can modify youíre water fill/drain plumbing, it will keep happening.
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Old 12-02-2021, 08:11 PM   #8
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Itís the siphon effect. Happens in my coach too. Once the overflow starts, thereís no stopping it until the water tank is empty.

Unless you can modify youíre water fill/drain plumbing, it will keep happening.
Does that mean your tank has an overflow tube all the way to the bottom? I donít question your post, but I cannot picture an overflow where the tube extends down so far. Why would it be built that way? Are some systems plumbed with the fill tube at the bottom and overflow somehow connected to that?
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Old 12-02-2021, 09:00 PM   #9
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I don't understand it either, but I used to own an Open Range 5th wheel that did the same thing. Other OR owners had the same issue.
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Old 12-02-2021, 10:00 PM   #10
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I don't understand it either, but I used to own an Open Range 5th wheel that did the same thing. Other OR owners had the same issue.
Bingo! I donít know the plumbing specifics, but I know that it happens ó for a lot of people.
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Old 12-02-2021, 10:27 PM   #11
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This one is definitely a little crazy, I have over filled my fresh tank a few times and never has it completely emptied itself. I tend to agree with Ljwt330 that it is an open weatherizing valve. It is possible that the overflow hose is connected to a fitting that has a dip tube in the tank by accident or design flaw. Design flaw sounds like the problem with the Open Roads units, though it is possible the tank supplier shipped a batch of tanks that was incorrectly fitted with dip tubes in the overflow location.
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Old 12-03-2021, 12:27 AM   #12
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Design flaw sounds like the problem with the Open Roads units, though it is possible the tank supplier shipped a batch of tanks that was incorrectly fitted with dip tubes in the overflow location.
Both the OP and myself own National RV units. Apparently, siphoning can be a ďthingĒ with them as Iíve heard similar stories from National RV owners.
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Old 12-03-2021, 10:49 AM   #13
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I never said that the OP's overflow mechanism (plumbing) emptied HIS WHOLE TANK. I said, it will empty what it will, until the water level is reached, where the overflow plumbing, CANNOT reach any more water. And therefore, you will have a full tank, but BELOW the overflow plumbing.

Now, if you, or anyone in any RV have or has an overflow system, that will COMPLETELY empty your tank, once it starts flowing, then there is some seriously flawed construction techniques applied when the tank and plumbing were built. THAT IS NOT NORMAL, by any means. NORMALLY, the tube that picks up the water as it approaches the ceiling of the tank, is around 1" to 1 1/2" below the ceiling of the tank. This is so that when filling, you don't run the risk of damaging the tank due to inattentiveness while filling and the water begins to run out the overflow, just prior to hitting the ceiling of the tank.

But, because the tip of the suction side of that overflow plumbing is as stated in length, and any form siphoning is taking place, the tip of that suction side will soon not be able to grab any more water and the siphon will be broken and the flow of water will be stopped.

If there's other plumbing issues associated with the OP's tank, well then that's a different matter.
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Old 12-03-2021, 10:52 AM   #14
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I think we have agreement that the draining is caused by a siphon.

What can't be explained is why the siphon appears to drain the tank completely when the overflow port is at the top of the tank, with no dip tube extending into the water.

I think I may have a likely answer to this oddity.

After looking at pictures of various fresh tanks that are found in different rvs, I noticed that some tanks had the fill port/line and overflow port/line at the top of the tank, on the side. Both ports/lines were 1/2" and were fairly close together.


Here is an example of this:





You will note in the picture that the fill line has a check valve installed.


Here's the key. The fill line from city water often had a dip tube going to the bottom or near the bottom of the tank, much like a typical water heater. This was to keep the water from splashing and making noise as it was filled. The overflow/vent port did not.

What may have happened on select rvs is the assembler or installer of the tank connected the fill hose and overflow hose to the wrong ports. This error could account for exactly what the OP and others have described. If the overflow hose is connected to the fill port, once the tank is filled the siphon starts and continues until the water level drops below the end of the dip tube.

The incorrectly attached fill hose has a check valve installed at the hose connection, so filling the tank completely would not lead to a siphon from the hose connection. Further, once water is used from the tank, the water level will drop below the port opening and the siphon will break.

To me, the above seems to be the least complicated explanation of this mystery. Anyone with a tank that has the fill port and overflow ports reversed could experience the siphon draining of their fresh tank once it is fully filled.
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