Tank plumbing mysteries solved! Mostly...

[Camper_bob]

Okay, so after thinking about it for a long time, I decided to just figure all this out once and for all.

For reference, my trailer is a 2014 Jay Flight 28 BHBE. My trailer has 86 gallons fresh water capacity (2-40 gal tanks, and the HWH). Since my trailer is completely open on the bottom, everything is relatively easy to see and trace.

The tanks are plumbed as follows: Each tank has a drain in the absolute bottom of the tank that flows to two 1/2 turn plastic valves labeled on the outside skirting of the trailer as a "Low Point Drain". Teed into the drain line from the rearward tank is the water pump pickup. This is all on the curb-side of the trailer.

On the street-side of the tanks, there is a 1.5" (?) equalization hose that is tapped into the side of each tank. This hose simply runs from one tank to the other and is there so that the tanks will fill "equally".

At the top of the tanks on the street side, there are two 1/2" (?) hoses to equalize air between the tanks; they also just run from one tank to another. At the top of the forward tank only are two air vent hoses that route behind the steps and allow air to enter and escape as the tank is filled or emptied.

Sorry about the low-light conditions of the pictures, I did this at about 9:00 at night after loading out my trailer for a trip.


This is from the street-side, looking at the rearward tank. You can see where the tank drain is tapped on the far left, and the line you see that looks like it's going into the propane block (teed between the tank drain and the tee for the drain valve) is the water pump pickup line, it goes straight up to the pump which is under the sink. You can see the rearward drain valve in the upper right foreground.


Here you can see the forward tank drain, and the forward tank drain valve.


This is the water equalization hose on the street side of the tanks.


These are the air equalization hoses (also on the street side) between the two tanks.


This is back on the curb-side from under the stairs. These are the two air vent hoses tapped into the top of the forward tank.


The fresh water gravity fill is up on the curb-side of the trailer above all this and goes into the top of the tank like normal, with it's standard vent line.

So, there you have it. Mystery solved, sort of. This is how it's plumbed on my trailer, as they say, YMMV.

The one big question I STILL have is this: Because of the location of the pump pickup line (teed into the primary tank's drain line), the pump should always be able to pick up water if there is water in the tanks that can be drained.

However, this is not the case. The pump will stop pulling water LONG before the tanks stop draining. And not just one drain, but both drains, and more importantly, the rearward drain where the pump pickup line is plumbed. How can this be?

The only thing I can figure is that there is not enough pressure? The pump is pulling more water than can be drained?

I have some mod ideas brewing here to make all this better ...

[mike837go]

Once the pump draw's air from the lower level tank, it's all over. The prime will be lost and you'll have a mix of air and water from the faucets.


Correct me if I'm wrong, but it looks like 1/2" PEX was used to link the tanks, drain and pump.


Seems oversimplified. Water can't move from the forward to rearward tank fast enough during filling and when below 1/4 tank, air is going to be a real issue!


Would you consider valves to control which tank is drawn from by the pump? That'll solve the air issue when low. Then upgrade to 1" or 1.5" for the link between the tanks?

[RVhiker]

Thanks for posting those pictures; I've never been able to figure out the plumbing of my two fresh water tanks (and I even got Jayco to send me the schematics, which did not seem to match up with what I was seeing under my trailer). My tanks are covered by the bottom coroplast on the trailer.

But I still have questions.

1) In the next to last picture, there are two "air equalization hoses" that seem to run just from the top of one tank to the other, and no place else. Is that correct?

2) In the last picture, there are two "air vent hoses" that are tapped into the top of the forward tank. Do these two also function as the two "overflow" hoses? Does one of these two hoses some how connect to the rear tank? If not, does the rear tank not have an overflow hose dedicated to it, and if overfilled it just runs through the larger equalization hose into the front tank and would then lose overflow water out of the two air vent hoses tapped into the forward tank?

[DEM]

My 2012 25RKS is piped almost identically.

[Camper_bob]

Originally Posted by mike837go

Once the pump draw's air from the lower level tank, it's all over. The prime will be lost and you'll have a mix of air and water from the faucets.

Correct me if I'm wrong, but it looks like 1/2" PEX was used to link the tanks, drain and pump.

Seems oversimplified. Water can't move from the forward to rearward tank fast enough during filling and when below 1/4 tank, air is going to be a real issue!

Would you consider valves to control which tank is drawn from by the pump? That'll solve the air issue when low. Then upgrade to 1" or 1.5" for the link between the tanks?

You are correct. I think the best solution at this point for tandem tanks like this (at least for me) is to isolate the second tank using some kind of valve in the water equalization hose. Then I can just fill the primary tank when I need it, and I can open the valve to use the other tank if I need to (which is rare). I also think the whole thing would benefit from larger drain/pickup hoses in that entire area. It seems like this would help solve the pump picking up air in the vortex issue; there would be more water coming into where the pump needs to pick up. I would also need to plumb a valve into the drain side.

Originally Posted by RVhiker

Thanks for posting those pictures; I've never been able to figure out the plumbing of my two fresh water tanks (and I even got Jayco to send me the schematics, which did not seem to match up with what I was seeing under my trailer). My tanks are covered by the bottom coroplast on the trailer.

But I still have questions.

1) In the next to last picture, there are two "air equalization hoses" that seem to run just from the top of one tank to the other, and no place else. Is that correct?

2) In the last picture, there are two "air vent hoses" that are tapped into the top of the forward tank. Do these two also function as the two "overflow" hoses? Does one of these two hoses some how connect to the rear tank? If not, does the rear tank not have an overflow hose dedicated to it, and if overfilled it just runs through the larger equalization hose into the front tank and would then lose overflow water out of the two air vent hoses tapped into the forward tank?

1) That's correct, two air equalization hoses that only go from top of tank 1 to top of tank 2.

2) Also correct, there is no dedicated overflow hose plumbed into the rearward tank (primary tank); only 2 plumbed to the top of the forward (secondary) tank.