Pipe Bumper Air Tank

[OnlyCummins]

I can't see any sort of steel cylinder creating shrapnel. All the pics I've seen of ruptured cylinders just showed a longitudinal split, presumably along the weld. And the only missiles created by ruptured cylinders or sheared valves that I've read about are the cylinders themselves. Back in my SCUBA days I can remember seeing pics & reading about SCUBA cylinders with sheared off valves going thru the trunk or tailgate of the car they were NOT secured in -- DUH!. Think it would be a non-issue with a bumper since it's attached to the vehicle. Just think of a pipe bomb: the pipe itself isn't what does the damage (unless its been scored to weaken it), it's what's inside -- the shrapnel. Another story if cast iron is used instead.



As for rear-mounted propane tanks being a dumb idea, those things are so overbuilt that they would probably be the only thing whole in a serious accident. Besides they're equipped with pressure relief valves AND propane is far less volatile than gasoline. What's dumb is folks running around with unsecured plastic 5-gallon (on up) gasoline filled containers in their vehicles. Now that's DUMB!

 

[esdd]

From the pics posted I seriously doubt that the tubing used is sch 40, most likely thinwall steel, If it were sch 40 the weight of this bumper would be in the range 500-600 lb. Figuring the volume of the bumper is simple 3. 14 (pi) x r (1/2 diameter) squared x 12 = cu in per linear foot, knowing that there is 1728 sq in per cu ft it would take 11. 5 linear ft of 4" pipe for 1 cu ft of volume. Being that I am a certiged welder, Hayes GA, National Board J,R, and N (Nuclear) stamps, and a working pipefitter, I can safely say that commonly available sch 40 carbon steel pipe is too soft for use as a pressurized bumper. As to the issue of schrapnel in the event of a rupture the pipe would probably fail adjacent to the weld, assuming a quality weld, and simply split open. If a threadolet or nipple were broken off it may become a projectile. There are bumpers on the market for large fleet service vehilces that are appx 12-16" in diameter and are certified for use by the NTSB, but these bumpers are fabricated of high tensile steel, not sch 40 pipe. In conclusion the low volume, high weight, and relatively low strength of an air filled bumper make it a poor choice as an air tank and a bumper.

 

[CMacKenzie]

As I said earlier, I have decided not to use the bumper as an air tank. I purchased a 2. 5 gal. tank and will mount it between the frame rails.



In this day and age I just don't want to take the chance of being sued. My wife (soon to be lawyer) said any personal injury lawyer would jump at the chance to handle a case where any large vehicle with a pipe bumper was involved in a wreck. The liberal juries nowadays would want to award the plaintiff more than the were asking for in damages and emotional distress due to the fact that the driver is probably a Conservative, drives a big ol' truck thats a fuel guzzler, and supposedly this is not a vehicle Jesus would drive.



Well, I've got to leave for my 2 week rotation off-shore tonight and since we don't have Internet access (only satellite intranet to Head Office) I will be back checking the forums in a couple of weeks.



Thanks for all ya'lls replys,

Charlie

 

[BIGDIG]

CMacKenzie. . I know your going to use a tank but..... I have the same bumper with the tow loops/light sleeves also. The side shot you poseted,look at it. On my bumper I noticed a month or so after installing it,that in that corner was a pinhole that water was seaping out of causeing a line of rust as it dripped out. no big deal,just drilled a couple of small holes to check for water,none,so I squeezed in some gasket sealer and no more water. The welds are your weak point,just letting you know so you can check. I had a 4x6 custom box beam bumper on the rear of my 85 ramcharger,I put the air fittings on it and put just enough air into it to inflate at the most one of my goodyear mt 37" hummer tires. just in case... . Theres no need to carry more. the bumper will not explode with that little air in it,even enought to fill 2 or 3 tires,it will just hiss out. witnessed this on a 4 wheeler before when it struck a rock. sounded like he tore out a sidwall. And Y-Not ,If you ever replied back to me like that even with an apology,I'd be knockin at your door. The guy asked a simple question,give him a simple and profesional answer... ...

 

[CRSmith]

I know you're not building a bumper, but thought I'd crunch the numbers to give y'all an idea of the forces involved anyway. If anything, to discourage others from trying it.



Boyle's Law is P1 V1 = P2 V2

P1 = Initial Pressure

V1 = Initial Volume

P2 = Resulting Pressure

V2 = Resulting Volume

(This is assuming constant Temperature which is not true, but close enough)



P1 = 120psi

V1 = (assuming 4" diam pipe, 80 inches long) 1005ci

V2 = (assuming after the collision the bumper is crushed to 1/10 it's original volume) 100ci

Solve for P2: P2 = 1200psi !!!



The force on an end cap would be 1500lb @120psi and 15000lb @ 1200psi !!!



Can you say KA-BLOOWEY?



To make this bumper safer (not completely safe), you could install about 5 blow off valves to release pressure over 200psi, or something.

 

[OnlyCummins]

Originally posted by CMacKenzie

... In this day and age I just don't want to take the chance of being sued. My wife (soon to be lawyer) said any personal injury lawyer would jump at the chance to handle a case where any large vehicle with a pipe bumper was involved in a wreck. The liberal juries nowadays would want to award the plaintiff more than the were asking for in damages and emotional distress due to the fact that the driver is probably a Conservative, drives a big ol' truck thats a fuel guzzler, and supposedly this is not a vehicle Jesus would drive. ...

If you're really concerned with the threat of litigation then ANY aftermarket bumper would provide the sue-happy sufficient cause to sue you.

 

[Midnite]

Originally posted by reduaram

V2 = (assuming after the collision the bumper is crushed to 1/10 it's original volume) 100ci

Solve for P2: P2 = 1200psi !!!



The force on an end cap would be 1500lb @120psi and 15000lb @ 1200psi !!!



Can you say KA-BLOOWEY?

I would be very interested to see how you could crush that bumper to 1/10th volume in a vehicle accident (or any other way, for that matter).



It's been mentioned that if a nipple broke off that it might become a projectile, but that would only be if the collision broke it loose from its mounts to the frame.



I'm not saying I think anyone should or shouldn't use a bumper like this, I just think some people are getting carried away with the theoreticals...



Mike

 

[CRSmith]

1/10th is an assumed value. What bumper crushing research do you have access to that would suggest this value isn't in the ballpark? Pick any value you feel like and do the math. The point is, pressure is inversely proportional to volume so we're not dealing with 'just 120psi' hissing out. Hopefully, any bumper would tear or split from the force of the impact without the air pressure inside rupturing it. Then the air would just escape with no damage.

 

[Midnite]

Originally posted by reduaram

1/10th is an assumed value. What bumper crushing research do you have access to that would suggest this value isn't in the ballpark?

I've got a Ph. D in Theoretical Bumperology!



I didn't mean to ruffle any feathers, I just think we're getting away with ourselves in many respects here.



Mike

 

[OnlyCummins]

Originally posted by reduaram

1/10th is an assumed value. What bumper crushing research do you have access to that would suggest this value isn't in the ballpark? Pick any value you feel like and do the math. The point is, pressure is inversely proportional to volume so we're not dealing with 'just 120psi' hissing out. Hopefully, any bumper would tear or split from the force of the impact without the air pressure inside rupturing it. Then the air would just escape with no damage.

To turn the question around: What bumper crushing research do you have access to that would suggest this value is in the ballpark?



Don't mean to take sides but I was thinking along the same lines as Midnite. I think it would be highly unlikely that any clyndrical object could be crushed to 1/10th its normal volume in any average accident. The only situation I can think of that possibly happening is if the bumper was impacted almost perfectly square against a very heavy wall/abutment/etc at a veeeeery high rate of speed. This scenario, of course, requires making certain assumptions about how its attachment points (frame, whatever, ... ) would react under the force of such an impact.



You shouldn't be surprised to have been called on your kinda far-out (IMO) assumption.

 

[kaffine krazed]

Semi trucks have air tanks for the brake system mounted outside the frome rail. I haven't heard about them blowing up sending shrapnal every where.

 

[JWhitcomb]

Couldn't this whole discussion be shut down by a pipe within a pipe bumper?

 

[illflem]

Originally posted by JWhitcomb

Couldn't this whole discussion be shut down by a pipe within a pipe bumper?

Or a real air tank under the truck?

Probably cheaper anyway.



I got a great deal on fertilizer spreader mounted on a GMC truck where the fertilizer box was too far back from the rear axle. It was no problem on the flat but on even a slight uphill incline with a full load it was wheelie time. I built the ultimate pipe bumper, 6'' well casing filled with lead. Sucker weighted close to a ton. Problem solved. Like to see what would happen if that one ever got in a wreck.

 

[OnlyCummins]

Originally posted by JWhitcomb

Couldn't this whole discussion be shut down by a pipe within a pipe bumper?

Well ... how about a pipe within a bumper? That's what I'd like to do. Not for safety reasons but to preserve the original 'lines' of the truck. One day ... more like, one year.

 

[Scheibins]

Y'all are funny.

I'm not going to add any more to this thread, as you know what I think from my previous post.

BUT... . if everbody who replied to this thread (I counted 19 at a glance) sent me 3 bucks cash in the mail, I think I could find the time (I work 3/12s) to go get the materials and weld up a "bumper air tank" to do a test on. WE (me and you guys) would be using 110psi in a 4" square tube the width of a Dodge CTD front end. Come up with an OFF auto test that everybody likes and see what happens.

What do you think? I'll video tape (only VHS available) it just in case I win a Darwin award .

 

[moparguy]

Scheibins, I know you're just joshing. But for those that don't know, there is a reason high pressure vessels are round. Ever see a air tank, oxygen or acetylene tank that was anything but round.



A square tube air tank would likely not be a problem with only a few pounds of air(well under a 100psig). But the only tank I'd consider welding up would be from proper pipe and a API certified welder would do the welding (I'm not one but know several), and it would use only proper weld caps at the ends. Flat iron or steel plate is a accident waiting to happen.



Now this tread can die a quite death.



RJR

 

[Scheibins]

Originally posted by moparguy

Scheibins, I know you're just joshing.



No, I was quite serious. If I knew how to post a picture I'd show you the one that was on my Scout. I'd didn't take any close ups, unfortunatly. It held 110psi in it plenty of times and as many times as backed up into tree or a rock, should be testimony for this whole thread anyway.



But for those that don't know, there is a reason high pressure vessels are round.



EXACTLY, high pressure, which is not what we are talking about here.



But the only tank I'd consider welding up would be from proper pipe and a API certified welder would do the welding (I'm not one but know several), and it would use only proper weld caps at the ends.



All this proper cr*p and certified talk should be saved for the High pressure (500+) bottle you're going use without an air compressor.



Now this tread can die a quite death.



Darn you, I said, I wasn't going to comment anymore and look what you made me do.



RJR

EDIT:

I guess I didn't do that quote thing quite right, but I'm still learning.



BTW, I know if I was making the tank out of tin foil I would want it to be round, but I'm not. It was 1/8" mild steel.

 

[moparguy]

You know this has turned into an enjoyable thread.



RJR

 

[Big White Beast]

Hmmmmm.......

Reduram, You peaked my curiosity.



What would the pressure be on a normal pipe bumper with welded ends. Plugging a zero into your equations doesn't work. I'm guessing that at sea level there is a certain amount of pressure anyway.



Crushing this pipe would lead to a pressurized situation also. Granted not as high as the 1200 you figured starting at 120 psi already in the pipe.



If you know what the pressure should be it would be interesting to plug those numbers in and see where a normal bumper would pressure up to?



Garrett

 

[jponder]

Re: Hmmmmm.......

Originally posted by Big White Beast

Reduram, You peaked my curiosity.



What would the pressure be on a normal pipe bumper with welded ends. Plugging a zero into your equations doesn't work. I'm guessing that at sea level there is a certain amount of pressure anyway.



Crushing this pipe would lead to a pressurized situation also. Granted not as high as the 1200 you figured starting at 120 psi already in the pipe.



If you know what the pressure should be it would be interesting to plug those numbers in and see where a normal bumper would pressure up to?



Garrett

Standard atmospheric pressure is 14. 7 psi so using his idea that the bumper would be crushed to 10%(that would never happen) you woul get a resultant pressure of 147 psi