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Old 07-05-2020, 01:50 PM   #1
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Question 14 gallons unuseable...

Just got back from our July 4th outing, and had the opportunity to run the fresh water tank dry again.


But, this time I was able to measure how much water we put back in to the tank... which turned out to be 34 gallons to overflowing out the gravity fill port. We have a 48 gallon fresh water tank. That means we have 14 gallons of unuseable water in our FW tank.



I've always felt like we were never able to get all the water out of our FW tank, and now I've confirmed it.


I've got an idea how to help fix this situation, but wondering if anyone has any ideas as well.



There are 3 support bars that the FW tank sits on in the camper frame. The tank sags down between these bars, and sags down at the ends. The supply line from the FW tank to the pump comes out of the FW tank roughly in the center of the tank...


I'll try to get some pics later that show what's going on.
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Old 07-05-2020, 02:17 PM   #2
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you also have 6 to 10 gallons in your water heater...
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Old 07-05-2020, 04:08 PM   #3
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Quote:
Originally Posted by formerFR View Post
you also have 6 to 10 gallons in your water heater...

Those are already accounted for, since they have been filled since de-winterization.
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Old 07-05-2020, 04:16 PM   #4
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Quote:
Originally Posted by BriaBeck View Post
We have a 48 gallon fresh water tank. That means we have 14 gallons of unuseable water in our FW tank.

Can I ask where you got the numbers from? The reason for this is that the current brochure for your RV states a 38 gallon fresh water tank.....but I may be looking at a wrong model.


https://primetimerv.com/files/brochu...erbrochure.pdf


EDIT: I used the wayback machine to check out the 2018 specific models and you are correct that it's supposed to have a 48 gallon freshwater tank, according to their brochure:


https://web.archive.org/web/20190518...erbrochure.pdf
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Old 07-05-2020, 04:43 PM   #5
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I put in support bars to get rid of the sag on mine. Another thing people do is use the drain port as the port that delivers water to the pump and either have a tee there so it also serves as the drain or just move the drain to the side port.
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Old 07-05-2020, 06:21 PM   #6
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Here's some pics of my FW tank...


There's not much water in it right now, so there's not much sag... but it looks a lot worse in real life than in the pictures.
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Old 07-05-2020, 06:37 PM   #7
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So both of yours are on the bottom which is good. When the pump starts running out of water, can you push up on the tank and feel how much water is pushing downwards?
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Old 07-05-2020, 07:05 PM   #8
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Basically, when the tank is down to the level where the pump is sucking air, the water is in the "sag bubbles" at either end. That's why I shoved that 2x4 up in there, just to see how much flex the tank had, to try to "flatten out" the sag at the ends, and maybe cause the water to pool to the sides. I know the 2x4 is a little too much, but now I know what I'm dealing with.


As the tank sits from the factory, the drain and the supply ports are the highest spots in the floor of the tank because of the sag at the ends.


I'm thinking of getting some 1/8"x4 steel strap, and cutting it to the width of the inside of the frame rails, and then welding some stops at the two outer supports, so that the strap is "trapped" and cannot bow down under the weight of the tank. I'll put one of these straps at the front 1/3 of the tank, and another at the rear third of the tank. I'll also weld some spacers at each end of the strap on the bottom side of the strap where it would lay on the frame rails, which would make the ends higher than the middle, and should cause the tank to sag to the center, rather than sag at the ends, and cause the water to pool in the center of the tank.


At least, that's my idea right now. If anyone has a better solution, I'm all ears!
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Old 07-05-2020, 07:17 PM   #9
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I'm just thinking, I've also got some 1 1/2" square tubing out in my shop... I could just use that between the frame rails and the support bar on either side, and let the tank sag to the center as well.


Looks like I've got a few options...
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Old 07-05-2020, 07:33 PM   #10
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Here's another fresh water tank support thread that motivated me to make some upgrades. Maybe worth a look to see what others did.

https://www.forestriverforums.com/fo...de-129346.html
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Old 07-05-2020, 07:36 PM   #11
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Originally Posted by BriaBeck View Post
I'm just thinking, I've also got some 1 1/2" square tubing out in my shop... I could just use that between the frame rails and the support bar on either side, and let the tank sag to the center as well.


Looks like I've got a few options...
Mine looks a little different than yours and doesn't really sag much. That said I have considered using some C-Channel or Unistrut to hold up what sag there is. (Unistrut is called "Super Strut at Home Depot).

If I place two pieces of unistrut from side to side I can merely use a J-Bolt to hook over the outside of the frame flange and tighten it up.

As an alternative to a J-Bolt a piece of flat laying on top of the strut and drilled for a machine bolt could clamp the strut in place.

This would also be part of my plan to run a piece of conduit underneath the trailer for some future wiring mods.
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Old 07-05-2020, 07:52 PM   #12
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Originally Posted by TitanMike View Post
Mine looks a little different than yours and doesn't really sag much. That said I have considered using some C-Channel or Unistrut to hold up what sag there is. (Unistrut is called "Super Strut at Home Depot).

If I place two pieces of unistrut from side to side I can merely use a J-Bolt to hook over the outside of the frame flange and tighten it up.

As an alternative to a J-Bolt a piece of flat laying on top of the strut and drilled for a machine bolt could clamp the strut in place.

This would also be part of my plan to run a piece of conduit underneath the trailer for some future wiring mods.

Hmmmmmmm.....


I'll have to see if I can get something over the top of the frame rails...
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Old 07-05-2020, 08:07 PM   #13
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I used large C chanel









This is the size difference to what was on it originally.


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Old 07-05-2020, 09:02 PM   #14
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Originally Posted by BriaBeck View Post
Hmmmmmmm.....


I'll have to see if I can get something over the top of the frame rails...
All you need to "get over" is the lower flange and just clamp. A large square plate washer may be all you need to clamp in the flange. No drilling required.
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Old 07-05-2020, 09:04 PM   #15
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I used large C chanel









This is the size difference to what was on it originally.


Certainly stout enough. Out of curiosity, how heavy is one piece of that C-Channel?
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Old 07-05-2020, 09:22 PM   #16
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Certainly stout enough. Out of curiosity, how heavy is one piece of that C-Channel?
Heavy and I didn't need to use that big. 2 pieces added around 70#
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Old 07-05-2020, 09:26 PM   #17
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Old 07-05-2020, 10:19 PM   #18
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Levelness also affects usable water space in your tank. This is why the tank may indicate "full" even though it is not and it can indicate 2/3 even when it is full (can't take more water).

How it is plumbed also effects when the overflow pipe "overflows" before the tank is full. Attempting to push water into the tank after the water is coming out of the overflow can pressurize the tank, rupturing it or bellying it out and breaking the supports.

Here are some photos and the service manual that explain the concepts.
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