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Old 10-14-2017, 03:02 PM   #1
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Bladder tanks?

Does anyone have any experience using these sort of transportable water bladders in a skoolie/RV context?



I'm intrigued for a couple of reasons. One, I'm hoping to be able to do long periods of off grid camping, and water is likely to be the limiting factor. Two I'm having trouble finding large capacity tanks in the right form factor to work under our bus (may need reinforcement, but our main storage bin is roughly 110" long, 96" wide, 12" tall under the frame, 22" tall on the sides) particularly for any reasonable price. Bladders are already in a reasonable form factor, and by nature can conform to the volume given to some degree. Third, I've got this wacky idea that by using bladders you could stack the grey water on top of the fresh water and effectively get both tanks to fit in the volume a single traditional tank would take up. For example, if you have a 100 gallon fresh and 100 gallon grey, that's 200 gallons of space taken up, but there's usually never more than 100 gallons of water between the two.

In my head I'm thinking of building a "tank" that would not have to be water tight, it's primary job would be to keep the bladders in place and contain and drain any leaks. The fresh water bladder would need to be on the bottom, since the grey water is gravity filled so it needs to be on top. As you use water it's pumped out of the lower bladder, and drains back into the top bladder. When the fresh tank is empty, the grey tank is full unless you've been taking outdoor showers or something.

As the grey bladder fills, the lower bladder will have a lot of weight on it. Using one of the examples below a 150 gallons of grey water would weigh about 1200 lbs. If spread evenly over the 60"x60" area, that's 1200 lbs over 3600 square inches or 0.33psi. Of course at that point the lower bladder would be empty and not really care. The load will not be completely evenly distributed due to the pillow shape and sloshing, but it would seem that they should push against each other and arrive at some sort of equilibrium so long as they are sufficiently restrained so as not to bunch up or roll around. That doesn't seem like too extreme a case, and could even allow for the lower tank to be refilled from a pressurized source if the grey tank was only partially filled. The bladders are not normally pressurized in use, but I have seen stress tests where one type were filled to double their rated volume by pressurizing.

Here are a few examples I've come across:

Potable Water Bladder Tanks

AQUATANK2 Water Storage Bladder (150 Gallon) https://www.amazon.com/dp/B009ONFDE2..._j8L4zbSSC40DD

Any thoughts?



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Old 10-14-2017, 03:03 PM   #2
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We call those "water beds" where I'm from.

No reason I can think of you couldn't use that, properly constrained.
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Old 10-14-2017, 04:39 PM   #3
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It's an attractive idea that will probably not work.

You are effectively pressurizing your fresh-water system, and while that might be okay if the pex and the joints can take it, filling the system, even with the empty grey-water bladder on top, is going to be problematic.

Why can't simply install two regular water tanks under the bed, or sofa, and join them at the bottom with 1 1/2" pipe. They would fill to the same level naturally and give you the capacity you want. Then add your grey water tank under the bus.
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Old 10-14-2017, 06:30 PM   #4
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That actually is a workable concept of check valves in the water lines are added and backwater valves in the grey water lines to the tank are added considering that the grey water tank lines are either graded/sloped or pumped to the grey water bladder.
The only other concern with bladder tanks full of liquid is in contains not them? The forward motion of braking/shifting the water forward is going to take a damn good restraint and bladder material.
I would also want a real good sheet of soft rubber or something to that effect underneath the bladder setting on the floor to help with abrasion.
Without finding my old notes? There are several companies out there that custom build plastic tanks for a decent price.
The only one that comes to mind is plastic oddities but I don't think that's the one for tanks? There once was an agri-supply company that would make anything you wanted.
Your system with bladder tanks is feasible but will require more inlets and outlets that they are showing and if they did have the taps needed would be hard to do and maintain in the situation you have described.
Each tank has to be vented to allow air out as filled and air in as drained. The bladder tank you are looking at should/might have a BS two way valve built into but you are planning on containing it it so all of that will have to transfer over in your containment unit that if each tank is not vented separately then you have your have your freshwater tank in the same space as your grey water space then your grey water expels gas and your drinking water tank sucks that air in? I think that is my easiest way to explain it? There are other ways to accomplish your idea! You seem very engineer smart.
Good luck
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Old 10-14-2017, 07:17 PM   #5
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Those are good questions, Jolly and Twigg. From reading my understanding is the bladders don't require air vents when filling, because there is very little air in them to displace, they lie completely flat when empty. That seems suspect to me, but I've seen it noted in several places.

I've also seen it said they can be filled either unpressurized through the top port, or pressurized through the drain port.

Containment would definitely seem to be key. Still working that out in my head. For sure I would be planning to build a box around them with roughly the same volume as the bladders. I like the thought of using the ones with straps or handles that could be attached to the containment box to help keep them in place. I'd also be tempted to put some sort of rigid divider in between the two that would raise and low with the level of the lower bladder and help keep the weight of the upper bladder evenly distributed and keep it from wanting to get down along side the lower bladder. Maybe even something on rails of some sort so it can only move up and down parallel to the floor...

Still lots to think about. It's intriguing to me primarily because we're going to be a family of 5 plus pets on the road full time, and are looking at interior layouts that have very little "wasted" space where folks might normally stash their fresh water tanks. For example we're currently looking at the rear bed being raised up to the level of the rear doghouse creating a play space under the bed. The bunks forward of that would all have integrated clothing storage drawers.


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Old 10-14-2017, 07:52 PM   #6
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Quote:
Originally Posted by miscrms View Post

Still lots to think about. It's intriguing to me primarily because we're going to be a family of 5 plus pets on the road full time,
Shoot dawg, 5 pets? That's an ark.

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Old 10-14-2017, 08:01 PM   #7
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Sorry, lost a comma ;)
Family of 5, plus pets

Not sure, might be worse...


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Old 12-01-2017, 01:52 AM   #8
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Bladder tanks?

Well, found a pretty good deal on the 150 gallon AquaTank2 bladders and decided I'd give it a try. Still thinking it over in my head, but my current thought is to buy a cheap used IBC tote and modify it to contain the bladders. The bladders are 48"x72"x12" filled, and the 275 gallon totes seem to be about 40"x48"x46". Here's a rough sketch of the modification, basically cut in half with one end opened on each half.







The metal cage would then be welded back together, and likely anchored up onto the frame above the belly storage box for added support. The plastic liner would have the edges curled over and/or melted back together to protect the bladder from the cage. I'll probably leave some access open to be able to see the levels and get the hoses in and out. The liner doesn't need to be water tight, just protect the bladder.

Thinking about a nylon strap webbing between the two to help keep them separated. Loose enough to let them expand, but hopefully tight enough to keep them from trying to shift next to one another. Seems like the sag or bulge of the webbing if itís attached halfway up the cage around the perimeter should fit the shape of the bladders pretty well as they fill. Maybe a rubberized webbing to help reduce sliding and rubbing?
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Old 12-01-2017, 10:58 AM   #9
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In your first post you say that the size and shape of your underfloor storage bay does not lend itself well to being used for water tanks. Why use it for that at all? I prefer to keep as much of my underfloor storage for storage, so I put all four of my tanks and everything else (house batteries, propane, auxiliary electric compressor, generator, spare tire, vented storage for spare lubricants etc.) elsewhere. With five people on board you will need every possible storage space, believe me! I don't know how your bus is configured, but I put two 110-gallon water tanks on either side of my fuel tank, the 115-gallon grey tank is under the frame rails just ahead of the rear axle, the 65-gallon poo tank is on the left just ahead of the rear wheels, and everything else is tucked into any other available space. This keeps my precious underfloor storage bay's space almost completely free for Stuff. (I did however put my water heater and solar equipment in there, but it's hanging under the floor above so I can still use the space under it.) Like you, I want to be able to boondock for extended periods, so carrying lots of everything is important, especially fresh water.

One thing that always makes me slightly nervous is when I see RVs with their grey and black tanks next to their fresh water tank, and with their fill and drain valves in the same area. To me, that is a cross-contamination accident waiting to happen. That's one reason my fresh system is separated by the 8'-long storage bay from the waste system. making it completely impossible to have any risk of cross-contamination if anything were to leak or malfunction.

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Old 12-01-2017, 01:06 PM   #10
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Thanks John, appreciate the input. The good/bad news is our bus has a ton of enclosed under storage.



That's really cool, but leaves very little open space underneath. The main box (rear two doors) is almost 10' long and goes all the way through. The front boxes stop at the frame, and the 100 gallon fuel tank is in between. Ahead of that are the air tanks, and then the spare tire. There is another air tank behind the main box in front of the rear axle, and another in the space opposite the stairwell on the drivers side. There is a small space behind each front wheel, I'm hoping the outside units for the mini-splits will fit there. There is a bit longer space behind the driver side rear opposite the battery box, though the transmission cooler and auxiliary heater are in that area.

There is a mostly wasted space between the frame rails above the big box, as the box drops down under the frame and goes straight across. Still thinking about ways to reclaim that space.

If you have pictures of how your tanks are mounted I'd love to see.

Rob
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