air tank bumper
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Thread: air tank bumper

  1. #1
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    air tank bumper

    I'm have some 3"x5" rectangular tube I'm planning on using for making a rear bumper on my 4x4. It's somewhat common to use bumpers as storage tanks with onboard air to actuate lockers, and I'll be running a pressure switch that cuts off at 110 PSI.

    Will my MIG welds for this be porous enough that they leak air, and is there anything I can do to prevent it? I have an OA torch that I could use to re-melt the welds, but I don't know if that would do any good. Obviously my experience level is pretty low with this, so any advice would be helpful.

    - James B

  2. #2
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    Re: air tank bumper

    It is possible to make this leak tight with MIG.

  3. #3
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    Re: air tank bumper

    a pressure tank out of square or rectangular tube is not a good idea pipe would be ok

    Chuck
    ASME Pressure Vessel welder

  4. #4
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    Re: air tank bumper

    An air storage tank is a potential bomb. Round is the ONLY way to go, using square or rectangular is BEGGING for trouble. I personal don't think a bumper that is there to protect you in case on an accident should be used for high pressure air storage. I would prefer to see an air compressor hooked up to the motor, this would also give you unlimited air, not just the capacity of your "tank"



    Also, as you admit,
    "Obviously my experience level is pretty low with this, so any advice would be helpful."

    NO ONE, but a certified welder should be building pressure vessels! Yes, you might luck out, but what if you don't? Picture yourself, a buddy, or a little kid, next to the end cap with over 100 psi blasting it into them....
    Just my opinion, not from a book, just from the road.
    Howes Welding Inc.
    www.howesweldinginc.com

  5. #5
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    Re: air tank bumper

    Quote Originally Posted by tessdad
    An air storage tank is a potential bomb. Round is the ONLY way to go, using square or rectangular is BEGGING for trouble. I personal don't think a bumper that is there to protect you in case on an accident should be used for high pressure air storage. I would prefer to see an air compressor hooked up to the motor, this would also give you unlimited air, not just the capacity of your "tank"



    Also, as you admit,
    "Obviously my experience level is pretty low with this, so any advice would be helpful."

    NO ONE, but a certified welder should be building pressure vessels! Yes, you might luck out, but what if you don't? Picture yourself, a buddy, or a little kid, next to the end cap with over 100 psi blasting it into them....
    I tend to agree with Tessdad on the low level of experience, and the materials will definitely come into play. But after looking at your post carefully, and thinking hard about what you are trying to do with it, I think you will be just fine with this project. I will give a few pointers, and a few reasons why it should not pose a problem: First and foremost, the pressure involved. 120psi is actually still low pressure. If a bumper with 120psi is pierced, there will be a windblast, but nothing enough to blow apart a piece of tubing. I agree 100% that this kind of system will not be safe with the high pressures related to CO2, oxygen, or nitrogen tanks. I would suggest no less than.120 wall thickness for the bumper. Not for air pressure, for impact resistance. As for porosity within the welds making it not feasible, there are a few ways to circumvent this: 1. Clean all the material. No wax, grease, paint. 2. Good weld penetration. 3 an escape route for gasses. You need to weld in a drain plug to eliminate moisture buildup. You rarely weld any structure shut, airtight without some porosity near the end of the weld. So, weld on a drain bung fitting on the bottom. You will be able to get good welds, and the tank will have its' drain. All are good things.
    Now, my reasons for saying this will work fine: I used to race motorcycles. We had air shifters on some bikes I rode. We had the frames welded shut to make an air tank out of the frames. On the drag bikes, we ran 300psi or so in the frames for shifting. Not many shifts, lasted the whole day. On our roadrace bikes, we would charge an aluminum chassis to 1800psi, and use the system for instant upshifts all day. I crashed hard, several times, and never did an aluminum frame fail due to air pressures. One of those crashes was 145mph at Willow Springs. The crash knocked all the hot air out of ME, but the frame held its' nitrogen charge. I offroad trucks, and lots of guys use the frames, bumpers, etc. for air storage for inflating tires, running an impact wrench. Keep the PSI under 300, and have a good time.

  6. #6
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    Re: air tank bumper

    Interesting reading guys, never even heard of that before this post. Neat idea!
    If you don't have the time to do it right, then you definitely don't have the time to do it over.

  7. #7
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    Re: air tank bumper

    We routinely use square and rectangular tubing on Folding machines in Industrial laundries for the frame members.

    These machines use lots of compressed to actuate air cylinders and blasts of air for folding and such. So given the proper wall thickness you can certainly build a safe air storage reservoir.

    My concern here is your welding profeciency.....

    It can, as stated above be a very dangerous thing to weld improperly... Please be very carefull ... As Dirty Harry once said "A man has to know his limitations".

    I know of a guy who was standing next to an air compressor when the copper pipe on the end blew off due to bad soldering. When he came back from the hospital he had quite a few stitches.

    Washman

  8. #8
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    Re: air tank bumper

    i'd use a real air tank from harbor freight or northern tool and find a nice place to mount it..

    i would not ever use a homemade bumper for compressed air..even if I was to make it..
    its downright dangerous...

    ...zap!


    I am not completely insane..
    Some parts are missing

    Professional Driver on a closed course....
    Do not attempt.

  9. #9
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    Re: air tank bumper

    I'd do it. Should be fine... But, If I were you I would TIG weld it.

  10. #10
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    Re: air tank bumper

    I think what alot of the statements are saying is why take a risk, there are alot of proficient and tech savy welders out there but in todays world if something went wrong and you built the tank you are liable! So take zaps advice buy a tank and install it and if the tank ever fails the tank builder is liable.

  11. #11
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    Re: air tank bumper

    I had a Ford F-350 years ago that had a factory made 4x4 sq tube rear air tank bumper that held 175 #. Can't remember the company but it had a pressure vessel plate on it. I made up a manifold with a gauge and a quick connect to inflate tires on junk cars. I could do 4 tires completely flat so the car would roll onto my trailer. Just my .02 ...Bob
    Bob Wright
    Salem, Ohio Birthplace of the Silver & Deming Drill
    http://groups.yahoo.com/group/southbend10k/
    http://groups.yahoo.com/group/sawking/
    1999 Miller MM185 w/ Miller 185 Spoolmate spoolgun

  12. #12
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    Re: air tank bumper

    Quote Originally Posted by alanaker
    I'd do it. Should be fine... But, If I were you I would TIG weld it.
    Dats a good 1
    If you don't have the time to do it right, then you definitely don't have the time to do it over.

  13. #13
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    Re: air tank bumper

    Quote Originally Posted by zapster
    i'd use a real air tank from harbor freight or northern tool and find a nice place to mount it..

    i would not ever use a homemade bumper for compressed air..even if I was to make it..
    its downright dangerous...

    ...zap!
    Anything from Harbor Freight has to be more dangerous than what you build..... Look at what he's trying to do, put it in perspective, and then think of the materials used. An air tank on a compressor is usually??.050 thick material for a 10 gallon-ish tank. To hold 120PSI. He is trying to contain about 10 gallons of air in a .120 thick 3x5 piece of rectangular. 120PSI. Be real here. That application is a no brainer for the intended use. I agree, if it were nitrogen or CO2, I would say no, but it is just a holding tank for the compressor. It won't even hold air full time. It will only be used when the compressor pumps the bumper full. DILUDEDOOO... if you would like some more info on bumpers like this from lots of guys who use them all the time, you can try a few sites to search. Pirate 4x4.com, or TTORA.com. TTORA is dedicated to Toyotas. But there is a lot of cross over info from other sites. Both are a wealth of practical info on your truck projects. I browse Pirate, I am on TTORA. Hope this helps you.

  14. #14
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    Re: air tank bumper

    Quote Originally Posted by Dipper Welder64
    I think what alot of the statements are saying is why take a risk, there are alot of proficient and tech savy welders out there but in todays world if something went wrong and you built the tank you are liable! So take zaps advice buy a tank and install it and if the tank ever fails the tank builder is liable.
    The instant you change ANYTHING on a pressure vessel that varies from the manufacturers' specs, all liability is out the window, on YOU. You can't so much as thread a fitting into the original bung on it and expect the original MFG to accept liability. If you change the drain plug on a tank, and it was not the one in the original spec, you are on your own. Put on a different air pump/ compressor, you are on your own. Add hard lines, fittings, you are on your own. Weld a bracket onto it to relocate it????

  15. #15
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    Re: air tank bumper

    I gotta go with Rojo on this one--- Not that much pressure and not that much volume to be that worried about. Keep it in perspective. It aint rocket science. Its a bumper with a little bit of pressure in it. Do it. Do it right. Be happy. I did.

  16. #16
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    Re: air tank bumper

    I'm comfortable that with wall thickness 3/16"" or better there should be good safety margin for a tank under 200 psi in the approx. bumper size mentioned. Your bumper tank will be way higher quality the thin cheapie air tanks from Harbor /Northern. Build it!

    If you painted your bumper tank black and left it out in the sun, the pressure could rise considerably higher inside. Probably a reasonable idea to add a 250 psi pressure relief valve somewhere facing away from where people are likely to ever be. www.mcmaster.com has several suitable pressure relief valves like p/n 48435K72 which cost $5.05 plus shipping and thread into an extra 1/4" NPT fitting you weld onto your tank.

    I love McMaster-Carr. They have almost everything...

  17. #17
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    Re: air tank bumper

    Quote Originally Posted by Rojodiablo
    That application is a no brainer for the intended use. I agree, if it were nitrogen or CO2, I would say no, but it is just a holding tank for the compressor.
    Loving this post, even though I have no intention of making one up. Question: why air but not nitrogen/co2? I know I'm showing my gaps here, but it's among friends anyway. Thanks!
    If you don't have the time to do it right, then you definitely don't have the time to do it over.

  18. #18
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    Re: air tank bumper

    Quote Originally Posted by Clanweld
    Loving this post, even though I have no intention of making one up. Question: why air but not nitrogen/co2? I know I'm showing my gaps here, but it's among friends anyway. Thanks!
    Just the potentially high air pressures. CO2 and Nitrogen can be charged up to2200psi, and if you were rear ended with that kind of pressure, you may see some...interesting things in your rear view mirror..I would actually rather have nitrogen, as it is a dry gas, the bumper would have less reason to rust from the inside. The rockcrawler crowd does this a lot, they use on board air compressors, and use the frames, bumpers, rollcages for air tanks. When I do the full cage on my truck, I will be porting all the junctions in the tube, and using the rollcage as a storage tank the same way.

  19. #19
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    Re: air tank bumper

    This has been an entertaining thread, for several reasons.

    To put some perspective on things, it doen't matter WHAT gas is compressed (within limits such as it doesn't decompose explosively at high pressures like acetylene, etc). The energy stored is solely a function of pressure and volume.

    For perspective, the gas in a 40 gal tank charged to 100PSIG has (roughly) the same energy as 1 stick of straight dynamite. In improperly made tank can, for example, a) be brittle, and therefore b) crack and throw shrapnel under even light impact. Not what I would use for a bumper.

  20. #20
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    Re: air tank bumper

    A real world comparison - Tire repairmen routinely hold a 10 gallon tank charged with 150psi air in their hands. To seat a tire bead, they dump the contents in a one second rush of air, by opening a 2” gate valve.

    Now you wouldnt want to be in the air blast, but the bumper failing is not going to flip the truck over or anything. 3 x 5 x 72 = about 4.5 gallons. Not much volume and no explosive generation of pressure, almost as soon as the bumper would start to fail, it would be empty, probably no chance of a projectile. As a compromise, maybe tuck a pipe inside of a rectangular tube?

  21. #21
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    Re: air tank bumper

    there is nothing wrong with one of these..

    Name:  air tank.jpg
Views: 3316
Size:  11.0 KB

    there is no way you are putting 10 gallons of air in a bumper..
    and it has legs and "mounting points" already

    ...zap!


    I am not completely insane..
    Some parts are missing

    Professional Driver on a closed course....
    Do not attempt.

  22. #22
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    Re: air tank bumper

    Your right zapster.
    231 cubic inches in a gallon.

    Proposed bumper with id of 3 x 5 x 72 = 1080 cubic inches = 4.6 gallons.

    ˝ the volume potential of the 10 gallon hand held tank or tire air cannon.

    Hardly enough to blow "stainless dude"... off the barbeque!
    Last edited by denrep; 12-03-2006 at 02:08 PM.

  23. #23
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    Re: air tank bumper

    I really don't care if he builds an air tank out of the bumper or not, but, knowing you need an inlet, outlet, tubing to and from, and should have a petcock for drainage----------------I wouldn't want all that crap on my so-called bumper. Especially if it's supposed to be a hard core 4 wheeler. I'd have it all ripped to crap in a week or less.

    I'd rather have a nice little reservoir discretely hidden up in a cubby hole somewhere. Nice neat little package that nobody knows is there and gives fail safe operation. That's the challenge.

  24. #24
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    Re: air tank bumper

    sandy is right! You can get one off an old truck, complete with fittings, drain valve, check valve and mounting brackets.

    Now, how about an auxiliary liquor supply in that front bumper?
    Last edited by denrep; 12-03-2006 at 02:22 PM.

  25. #25
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    Re: air tank bumper

    [QUOTE=enlpck]

    For perspective, the gas in a 40 gal tank charged to 100PSIG has (roughly) the same energy as 1 stick of straight dynamite.

    Care to share where this came from?

    That ready made Northern air tank would be easy and convenient...

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