Bumper as an air tank - Would it work??

robert

Expedition Leader
Viair makes several sizes or air tanks that you may find works for you. They also have pressure relief valve and all the fittings you may need.
 

R_Lefebvre

Expedition Leader
I witnessed an extremely rectangular "tank" with 1/4" walls try really, really hard to become round at what ever a Thomas 12 VDC compressor can put out at max. They abandoned the idea after that.

For real? What were the dimensions of the tank? I find that incredible. I've never attempted this myself but, it just doesn't jive with my instincts.

To me, 125psi of internal pressure on say... a 2" square 1/8"wall tube is a very small effect.
 

ntsqd

Heretic Car Camper
They were primarily running board/rocker-knockers on a Dura-Max Extended cab truck. The truck was sold over a year ago, but what I recall is that the tube used was 2 x 8 and they could have been 2 x 10. The fabricator thought that they might bulge so he put in a string of 1" round holes down the center of the wide face and welded in some 1" round tubing. I don't recall what the center distance was, but a guess of 12"
Max bulge between the 1" tubes was about an additional inch total. It was never measured as the visual was enough to cool any further interest. If you know where to look the bulging should still be visible.
 

R_Lefebvre

Expedition Leader
Ok, on a 10" wide section, I guess I could see it. But with 1/4" wall? Wow. Still, I'd think on a typical 2x2, I'm not doubting it would bulge, but probably would need to be measured with calipers.
 

Remote

Observer
To me, 125psi of internal pressure on say... a 2" square 1/8"wall tube is a very small effect.

You are correct, a small tube like that should be fine. Just keep in mind that 125 psi means just that. Every single sq in is "holding back" 125 lbs. As the area of a flat surface increases, it does not take much before tremendous loads accumulate. Picture a 6" x 6" square plate; put 125 psi behind it and it is trying to resist 4500 lbs! It is an incidence thing. That's why round or cylinder shapes are used. The loads then become a tensile thing. The force is trying to "stretch" as opposed to "bend" or "deflect" a flat surface. Also the stress is uniform across the surface of the round and not accentuated at corners and such.
 

ntsqd

Heretic Car Camper
I think that the part of a square or rectangular pressure vessel that bothers me the most is the welds holding the flat end caps in place. They're getting hammered! :Wow1:
 

R_Lefebvre

Expedition Leader
Aren't the forces on the end caps relatively much the same as those on a similarly sized tube?

I just have trouble with the concept that a 2x2x.125" square tube has that much trouble with the same pressure being handled by my cheap air pig that is like maybe 12" diameter and made of... 22ga?
 

w squared

Observer
The amount of time it would take to rust out a bumper from internal condensation would, in most cases, be longer than the useful life of the truck. It's no different than the tank on an air compressor. And in Phoenix, where the OP lives, the problem would be pretty insignificant. I live in an area with a very damp climate, and my 40 year old air compressor tank has yet to rust through.

Agreed...but I bet that you probably bleed down your tank with a valve on the bottom when you're done with it, right? That will let most of that moisture out. That may or may not be viable on a bumper. I know that I want the bottom of my bumper to be both smooth and capable of withstanding some serious abuse (it actually blends into my front skidplate)
 

Grim Reaper

Expedition Leader
ran rock sliders made out of 4x4 box 66 inches long with 3/16 walls for years. They weighed a metric butt load.

I busted a rather large chunk off the ledge at fains ford in Tellico with them. Had a blow off valve rated at 140psi. At 140psi I could raise 4 BFG KM's from 14psi up to 20 psi. It was enough to help get to a gas station. I was able to reseat a bead with them but only had one shot.
 

ntsqd

Heretic Car Camper
Aren't the forces on the end caps relatively much the same as those on a similarly sized tube?

I just have trouble with the concept that a 2x2x.125" square tube has that much trouble with the same pressure being handled by my cheap air pig that is like maybe 12" diameter and made of... 22ga?
The end caps will be wanting to take on a hemispherical shape, so the welds around their perimeter will have all sorts of bending and shear stress' on them. They'll be getting pulled 6 ways from Sunday just by the air pressure.
I'll venture that it's thicker than 22 gauge, but it's all Hoop Stress when round. Not so much when it has corners.
 

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