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Old 12-23-2011, 09:58 PM   #11
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Re: another couple of water tank questions

I design above ground long term spent nuclear fuel rod storage buildings. Ask me a question.
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Old 12-26-2011, 02:42 PM   #12
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Re: another couple of water tank questions

Just fiddlin' around and actually calc'd the parts OP is using -

In inches and pounds, but, well, just call me an Ugly American - only the comparisons are needed and they can by anything, as long as they're the same -

Using 1-1/2"x1-1/2"x1/8" angle (don't know the thickness of OP's angle) and 24" lengths -
Bending stress on the iron is about 5300 psi. The strength of A36 steel - about the most common around, propbably similar to what OP has, is 36,000 psi - so there's about a 7 times safety factor. Seems like plenty, if you tank's getting more than this you'll probably be more worried about finding a doctor than about what happened to your tank.
Just for a 'quick check', NFPA 1192 specifies that propane tank mounts must be able to sustain a force of 8 times the full tanks weight in any direction, so we're comfortably in the safety ballpark.

Bolts OP is using have a yield strength of about 9000 lbs, supporting 100 pounds each - well in the 'safety zone'.

Deflection at the center of the bar will be about 0.001" with a full tank. About 1/3 the thickness of common typing paper.

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Old 12-28-2011, 11:19 AM   #13
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Re: another couple of water tank questions

Personally I would go with the 12mm bolt if possible. Look at the fuel tanks in most north american vehicles. They usually range from 80 to 130 litres, I have never seen one held in with 5/16" bolts. More often than not they are 7/16" (11mm) or larger. When you consider the thread depth on a 5/16 (8mm) bolt, is there even a 1/4" of steel left? Think about it, we use 1/2" grade 8 bolts to hold a 5000 lb hitch on your truck according to the math I'm seeing here, 5/16" bolts would be fine. We have to remember that tensile ratings are done in a lab with perfect conditions. They don't take into account the amount of corrosion a bolt will see (most bus seats are held down with 5/16" bolts, how many of those broke from being rusted thin?) Also if a bolt is over tightened when installed it will stretch, which also causes it to be thinner and weaker than spec. When it comes to hanging tanks, you can't go wrong using a bigger better bolt. Plus you have piece of mind...my 2cents
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Old 12-28-2011, 12:14 PM   #14
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Re: another couple of water tank questions

In every example you gave above the bolt is designed to resist failure in shear, not in tension.
Bolting a tank up tight between an angle bar and the truck frame puts the bolt almost completely in tension.
They're different.
Larger bolts are called for in every application that you mentioned, it's just that none of those applications are the same as OP's.

Quote:
When you consider the thread depth on a 5/16 (8mm) bolt, is there even a 1/4" of steel left?
The bolt strength is given for the size of bolt - you don't make 'adjustments' like that.

Just me, a bolt holding less than 10% of it's yield strength is fine with me, not sure how much more 'safety' you'd want than that - why not 3/4" bolts - lots 'safer'.

To each his own tho', just wanted to show OP the conditions and let him decide.

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Old 01-03-2012, 02:43 AM   #15
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Re: another couple of water tank questions

Have any of you looked at a 30 year old camp trailer??? One that's been used a lot with good sized holding tanks under it??? Pretty simple mounting under them... Just sayin'...
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Old 01-03-2012, 05:47 AM   #16
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Re: another couple of water tank questions

some of them have really large ones.... ive scrapped 5 for parts this last year and the 81 monico i am not quite done with has a 70 gal grey tank..
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Old 01-10-2012, 03:28 AM   #17
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Re: another couple of water tank questions

Thanks everyone, that's been very helpful. I thought I'd replied already but it's disappeared. Tom, that's great with those final calculations, cheers.

We decided to sandwich with ply and use the materials mentioned earlier.

I have another couple of questions

- I don't have any easy way to vent the greywater tank above the truck (no black water). Can I just put a small 1/2" vent in the top of the tank? The tank is a 200L plastic barrel, so I was just going to screw it in. The outlet hose for emptying is around 45mm diameter. I gather there are two issues here: smell, and equalising pressure for emptying. Does the vent need to be open when the tank is not being emptied (i.e. when tank is being 'filled' from kitchen or bathroom)? I'm using a hepvo valve under the sink and 45 then 50mm hose to the tank.

- does it matter where I put the water pump in relation to everything else? Closer to the tank or the kitchen tap? Closer to the califont? It's a sureflow 10L/m

- we're going to lag the freshwater pipes (12mm garden hose, it's not for drinking water), and before winter I will need to do something with the pump, but what about the fittings? I got told today that the small metal ball valve I was using needed frost protection (it has a plastic part inside). But will the other fittings be ok? They're a mix of brass and plastic. A hard frost here would be -10C (that's -14F?)
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Old 01-10-2012, 03:44 AM   #18
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Re: another couple of water tank questions

the grey water tank or tanks all need to be vented, but dont need large vents to function so 1/2 inch or 3/4 is overkill, but they have to always be vented and above the level of the tank by quite a bit. I have two of them (out of my 5) that have 1/4 inch vents.
the pump goes after the fresh water tank, and newer ones have a check valve built in. the pump can go just before the split for the hot water heaters and your cold supply for the shower, etc. its location doesn't matter a great deal as long as it constantly gets water from the bottom of the fresh tank. fresh water supplies should be inside the bus unless of course they are in an insulated compartment, and one can always have a small duct from the furnace to the compartment if desired.

you can look up the plumbing diagram in archives for proper fresh water diagram, just make sure you have a check valve either in or after the fresh water pump, and one in the city water hose connection for when you are hooked up to city water. The check valve at the pump is there not to allow the city water to fill your fresh water tanks and flood everything.
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Old 01-10-2012, 04:02 AM   #19
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Re: another couple of water tank questions

What's a check valve? The freshwater tank is outside. I'm not so worried about it and the frost (just the things that will break as opposed to freeze like the pump or the califont), but will probably look at some insulation at some point. The freshwater tank has a vent/overflow, and fills from the side of the tank. I don't have a system for using mains pressure water direct.

I'm pretty clear about the plumbing diagram, just wasn't sure if it mattered if the pump was at the tank end or the tap end. At the tank end would be better in my case in terms of access and noise. I'm thinking of building it into a small box. Any guidelines on how much insulation it needs? Does it need air around it inside a box or can I wrap it in insul blanket?

With the greywater, what happens if I have a short vent? How short is short?
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Old 01-10-2012, 10:14 AM   #20
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Re: another couple of water tank questions

a check valve only lets the water flow one way.. in the fresh water tank pump, it is designed to not let water flow back into the fresh water tank. The plumbing diagrams may or may not show this check valve in the system. So always install the pump in the direction of the water flow. I have 3 of them, and two of them have a arrow on the pump head.

the electric pumps are pretty quiet, and i don't see any need for additional sound insulation, but they need securely mounted. I use flexible line on each side also, and secure those back about 6 inches from the pump also. If water tank is undernieth the bus, then it should be well insulated, or heat tape.

Most vents that i have seen for fresh water go at least a couple of feet above the level of the bus, (or to the water inlet panel) They also serve as an indicator that the tank is full, so mounting these small tubes where you can observe the end is a good idea.
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