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Old 10-20-2012, 10:03 AM   #1
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Default Gravity feed potable water holding tank

Potable water holding tanks seem to always be found beneath the truck. This means using a pump to move the water around to where you need it. I'm wondering about using gravity instead. Does anybody have any experience with a water tank mounted high in the box? Will it supply adequate pressure?

For my thought experiment, I placed four load locks into the upper rails (at the forward part of the box). This resulting in a 2' deep platform the width of the box. Since I go 260 pounds and can easily hang from one load lock without any worries about it giving way I figure four of them supporting a holding tank (with the bottom being about 7' from the floor) might work out nicely. Especially because this is otherwise dead space above a toilet and shower stall.

I'm thinking 95 gallons is a sizeable potable water holding tank. This works out close enough to 800 pounds to call it. Add in for the mass of the holding tank itself and some plywood and we're at 850-900 pounds. Yes, this is a lot of mass mounted high and I may use a cable system to restrain it further but nevertheless, I don't think it will mass enough when full to present a significant roll over risk. Thoughts?

This 95 gal tank seems suitable. if you know of other, perhaps less expensive sources I would very much welcome your input. S-W2095 | 95 Gallon Rv Water Tank

Meanwhile, I've also investigated corner shower stalls from Lowes and learned 34" and 38" radii are typical. Installed beneath the four load locks leaves plenty of clearance (without feeling cramped).

Does anyone have an opinion on whether gravity supplies enough pressure when the tank is only 1/4 full? I can always install a pump but my being a KISS kind of guy by nature means I'd much rather eliminate it.
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Old 10-20-2012, 10:49 AM   #2
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General rule of thumb in a vehicle is to keep the weight as low as possible, 95 gallons of water at 8.4 pounds per gallon is 798 pounds plus the weight of the tank and supporting structure. Granted in a truck this is not a huge amount of weight, but far more that I would want mounted that high above the axles, and it is enough to have some affect on the overturning ratio of the vehicle. Water in a tank is considered a dynamic load rather than a static or dead load, once the tank becomes less than full you have the water weight moving side to side and that will shift the center of gravity to the out side of a corner. probably would not feel it too much in everyday driving, but could be a factor in an avoidance situation contributing to a roll over.

Assuming the tank is mounted at 7' giving an average of 8' to the top of the water, the static pressure at floor level will be 8 feet *0.43 psi per foot or around 3.4 psi. will be less at faucet height. While this will allow water to flow from the faucet it will not be much, filling a toilet, taking a shower and such would not be satisfactory. Standard house pressures are 30-60 psi. Sure flow RV water pumps have a shut off pressure of 45psi. and a running pressure around 30 depending on fixture being used and pipe size. With RV plumbing and fixtures having a smaller size, you will get around 3 gallons per minute with one of these pumps.

For my two cents I would mount the tank at floor level, with Sure-Flow on demand water pump.

Dave
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Old 10-20-2012, 11:44 PM   #3
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the pump will be cheaper than cost to support 95 gallons overhead.
good luck

-blizz
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Old 10-21-2012, 01:32 AM   #4
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Default water tank

If you are planning to feed a shower with the overhead tank, your press will be very little. Have you ever used a camp shower (a plastic water bag you hang from a tree) ? You can get wet and it is better than no shower but not much press. Are you going to need 95 gal? Are you going to heat water. You might think about removing the drop axle and put a tank under the truck. Just a thought. Good luck Kenn
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Old 10-21-2012, 09:02 AM   #5
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I agree with all these guys. With most things that move you want the weight low ... except probably a woman and then high is optimum.

It appears you're mounting the tank in the front of the box. More weight on the front axle. By moving the water taken further back (even behind the rear axle), you'll have much better weight and balance when you're done.
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Old 10-21-2012, 12:05 PM   #6
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Yes, locating the water tank above the shower is largely driven by consideration of the reduced 'basement' cube available in my particular truck (due to an auxiliary axle).

While an obvious concern centers on the 1000 pounds of mass (95 gallons plus tank and structure) mounted high, e.g. posing an increased roll over risk, this is offset by the simple fact the 22,400 pound truck is a) designed to carry 30,000 pounds of cargo, and b) it's not a sports car anyway. Regardless, I'm sanguine about this risk and on balance (pun intended) don't think it's a deciding consideration.

Adding a pump makes good sense since the camp shower analogy is valid. I had just hoped maybe it wouldn't be necessary. In any case, in the event I don't have electricity, I doubt an impeller reduces the flow in any significant manner and a camp style shower is better than none!

As for why 95 gallons? It's because a 110 gallon container costs $120 more. However, just becasue I can fill it doesn't mean I always have to. Maybe I just fill it 1/3 full, e.g. for a two day event. I think it's nice to have the capability of toting a fair bit of potable water as I cannot foresee all circumstances and too much is better than not enough.

Meanwhile, since I have an auxilliary axle, I believe I can take advantage of it. For example, I can lower it onto stacked 2x12 boards to, in effect, raise the drive wheels. This means it's a built in jack to facilitate changing a flat. Add a 5T bottle jack and I can do the deed for the steer tires also - without a service call. Moreover, I figure routing an air line (the truck is in essence a huge air compressor) into and around the box means I can carry an impact wrench for the times I need to change a tire.

However, thinking laterally, placing boards beneath just the low side makes it easy to level the box side-to-side, which is less expensive than installing leveling jacks (and probablty 90% as useful when you consider my truck is equipped with a squat option, which lowers the back of the box as much as 6 inches). Anyway, this is why I am loathe to remove the auxiliary axle altogether to sell it off to make room for potable and black water storage tanks - not when there may be another way.

Finally, with respect to balancing the truck, I understand what you're saying about front loading bias and agree 100%. However, I don't expect the gross weight to exceed 26,000 pounds in any case (though I'll weigh it when I'm done). Naturally I'm shooting for as even a distribution as I can reasonably achieve.

For example, offsetting the shower, toilet, and potable water in the forward part of the box is the 700 pound Harley in the very back (aft of the axle). I don't expect a lightly built interior wall and door to go much over 100 pounds. Added to it, a refrigerator and microwave combine for another 100 pounds also forward of the axle. However, my Honda ES6500 generator is about 350 pounds, plus 40 gallons of gasoline and a tank with mounting brackets amount to about 300 more pounds (650 total) of which both mounted aft of the axle.

Furthermore, the workbenches (two) will be aft of the axle (though they only weigh 100 pounds each it adds up). Meanhile, a Murphy bed mechanism (plus mattress) amount to maybe 200 pounds give or take, mounted forward of the drive axle. However, all in all, I don't think balance will be a huge issue.

In closing, after adding everything up, this leaves about 2500 pounds before I get to 26,000 pounds for things like a retractible awning, steps, a television, plus a few other items I'm forgetting at the moment.
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Old 10-21-2012, 12:34 PM   #7
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Personally I would never trust a tag axle for supporting a loaded truck to remove a tire. I am not sure what type of axle it is and how it operates, but all the ones I have used on the big rigs were air bags, and meant to supplement the main axles(s) not replace them. I have seen several of these axles blow an air bag when they had too much pressure in them and the truck went over a rise such as a railroad crossing. Makes for a hell of a bang, and would not want to be anywhere near it when it went. If you do go that way make sure you place a jack stand or something under the frame before working on or under the rig. Have not seen too many air suspensions that will maintain air pressure for too long with the engine off. With your truck being only partially loaded to capacity you probably would not have an sudden collapse issue, but I would not be putting my head down there to take a tire off. Bottle jacks are pretty cheap (I use a couple of them on my current moterhome for a poor man's leveling system) Running air lines is a great idea, never hurts to have a source of air for inflating tires, beach toys, and running air tools.

I would defiantly leave the tag axle under the rig at least until you have reached the point where you have most of the weight installed, then you can run down to a scale and see what ea axle weighs. If it is forward of the rear axle and you end up with a bit much weight on the front axle, it may help lighten the front end. Its almost always the front axle that gets overloaded on the conversions.

Good luck with your project.
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Old 10-21-2012, 12:53 PM   #8
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You're 100% right . . . my fat ass won't be under there without a jack stand!

Anyway, you're make my point, I can always decide to remove it later - but for now - building and planning around it (especially considering how lightly loaded the truck will be) makes leaving it seem like a no brainer.
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Old 10-21-2012, 06:05 PM   #9
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Quote:
Originally Posted by jbeech View Post
Finally, with respect to balancing the truck, I understand what you're saying about front loading bias and agree 100%. However, I don't expect the gross weight to exceed 26,000 pounds in any case (though I'll weigh it when I'm done). Naturally I'm shooting for as even a distribution as I can reasonably achieve.

For example, offsetting the shower, toilet, and potable water in the forward part of the box is the 700 pound Harley in the very back (aft of the axle). I don't expect a lightly built interior wall and door to go much over 100 pounds. Added to it, a refrigerator and microwave combine for another 100 pounds also forward of the axle. However, my Honda ES6500 generator is about 350 pounds, plus 40 gallons of gasoline and a tank with mounting brackets amount to about 300 more pounds (650 total) of which both mounted aft of the axle.

Furthermore, the workbenches (two) will be aft of the axle (though they only weigh 100 pounds each it adds up). Meanhile, a Murphy bed mechanism (plus mattress) amount to maybe 200 pounds give or take, mounted forward of the drive axle. However, all in all, I don't think balance will be a huge issue.

In closing, after adding everything up, this leaves about 2500 pounds before I get to 26,000 pounds for things like a retractible awning, steps, a television, plus a few other items I'm forgetting at the moment.
What is the "ideal" front/rear balance range for a truck? I suspect that the truck engineers can provide with a range to work with.
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Old 10-21-2012, 07:00 PM   #10
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be VERY careful of the front axle weight, the door sticker will tell you how much you can put on that axle. that is your number, you cannot exceed it. If you do, you may be lucky and never be scaled nor get in trouble for it. BUT! if you were to blow a front tire and someone gets hurt, all bets are off and you as the upfitter will be liable. If you ever want to sell it, the buyer will want to see the scale tickets and I'd hate to see you loose thsale over a overweight front axle. Rear axle shouldn't be a problem, 26,000 or under great, overload the front axle-bad, very bad.
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