fresh water tank fill

[Mike Labath]

I have a 397TH with auxiliary tank. When I fill the fresh water tank per manual,, The rear overflow spills and I stop. I go inside to check onecontrol and It only reads 1/3 . I tried to fill from the auxiliary water fill. and again, only the rear overflow went. It filled for another 10 min. I went inside and now shows 2/3. How do I get the forward tank to overflow and get the fresh water to read full. What am i doing wrong?

[Country Campers]

d2reid

Can you help this owner?

Other 397TH owners have any input?

Brian

[JBill9694]

Not a 397TH owner, but do have the auxiliary water tank, so will pitch in here. First to make sure we start off on the same page, the two tanks are connected by a small diameter line (I haven't actually looked at this line so some supposition here). Probably about 1/2" diameter and hopefully running level between the two tanks. As the primary tank fills, some water flows into the auxiliary tank, usually not as quick the primary tank is filling so the primary tank overflows before the auxiliary tank is completely full. If allowed to sit, the water level in the two tanks will equalize, or the auxiliary tank fill can be used to top of the auxiliary tank.

When water in the tanks is withdrawn via the water pump, it is pulled from the primary tank. Water in the auxiliary tank will then flow into the primary tank through the restricted connection to equalize the water level in both tanks. BTW, it is possible to drain the primary tank and still have water in the auxiliary tank, just wait until the auxiliary tank has time to recharge the primary tank.

Now here is the weird part. I too have had the auxiliary tank overflow start passing water before the primary tank overflow does, while filling the primary tank. This has happened after I have used some of the water out of the primary tank and am topping the water off for the next two to three days. (I have not had this happen when starting with both tanks drained.) For this too happen, the water level in the auxiliary tank has to be higher than that in the primary tank, which is not impossible, and there has to be pressure in the primary tank that is forcing water into the auxiliary tank so that it fills before the primary tank. Since the overflow should also be acting as an air vent, this should not be possible, but it is happening.

This might be related to the dreaded siphoning effect that others have reported, but even then the primary tank would have to be pressurized to start the siphoning. And on my tanks, at least, there is not an excessive amount of water from the overflow so I don't think it is really siphoning.

So in response to Mike Labath : Beats the S___ out of me. Let me know what you find out.

[Country Campers]

GDRV-Megan

Is there anything that you could add to the question in post #1.

How does the fresh water tank system work?

Brian

[Canyonlight]

I have a 397TH with auxiliary tank. When I fill the fresh water tank per manual,, The rear overflow spills and I stop. I go inside to check onecontrol and It only reads 1/3 . I tried to fill from the auxiliary water fill. and again, only the rear overflow went. It filled for another 10 min. I went inside and now shows 2/3. How do I get the forward tank to overflow and get the fresh water to read full. What am i doing wrong?

bob - has a 397 and possibly he may chime in and have some feedback. Thanks, in advance Bob !

Dan

[d2reid]

d2reid

Can you help this owner?

Brian

Sorry, single fresh water tank.

[JBill9694]

After I hit Post on #3 it occurred to me that the overflow inlet on the auxiliary tank may be mounted lower than the overflow inlet on the primary tank. If that is the case then the following scenarios are possible:

Starting with both tanks empty and using the primary tank fill; The primary tank will fill faster than the auxiliary tank and so water flow out of the primary tank overflow first.

Starting with both tanks full to just below the overflow inlet lip on the auxiliary tank and using the primary tank fill; The primary tank will still fill faster than the auxiliary tank, but if the auxiliary tank water level is right at the lip (invert) of its overflow inlet water can flow out of the auxiliary tank overflow before it flows out of the primary tank overflow.

Starting with both tanks holding water, but with the water level well below the auxiliary tank overflow lip and using the primary tank fill; The primary tank will still fill faster than the auxiliary tank and water will flow out of the primary tank overflow first.

What all this means is that regardless of which overflow the water first flows out, the tanks will drain until their water level is equal and even with the lip of the lowest overflow intake.

[howson]

rickcwagner -- moved your question to it's own thread. See https://gdrvowners.com/forum/operati...s-on-panel-why

[flyfshrockies]

In my mind I wonder how much effect is caused by the leveling of the r.v.?

Dave

[JBill9694]

I think there are several factors that could be influenced the water level reading and the overflows, flyfshrockies , the leveling of the RV is certainly one of them. The location of the overflows, height wise, to each other, the size and routing of the line connecting the two tanks, and if one of the overflows is plugged are other factors as well as the actual installation of the sensors (still haven't ruled out that the sensors are not properly installed and functioning. But at the end of the day, the two tanks should level out to the same atmospheric water level.