Landracing Forum
Tech Information => Technical Discussion => Topic started by: NathanStewart on February 11, 2012, 03:35:14 AM
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Long story short, I'm building a car that has air bags in the rear suspension. Looking for a small air tank. Don't need much capacity; only 1-1.5 gallons but don't have much room to work with. Can do long and kinda skinny but not short and fat. Need to do the math but something in the 3.5"-4" diameter range and however long to get me my desired capacity. Max pressure is 150 psi.
So why build my own? Because the supply of small 1 gallon tanks is pretty small (at least from what I can find). Also, it seems like a lot of cheap, poorly made crap has infiltrated the market and I don't trust a $40 tank from eBay. Seems like a lot of tanks are being made out of some very thin material these days. In fact, I've seen more than a few pictures of air tanks that have exploded and it looks to be from poor construction quality or thin material (16 gauge sheet maybe?) or both.
I'd like to do stainless or aluminum for corrosion resistance but steel is also doable. I've found 3" sch10 stainless pipe and pipe caps from a local place. Is sch10 (~.110 wall thickness) enough for 150 psi or would sch40 be better or would it be overkill for 150 psi? Or is my pipe dream going to give me a pipe bomb that'll blow off the back of my car?
Any suggestions or advice would be greatly appreciated.
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Tanks are safe to test if they're filled with water .
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I think sch. 10 is a little thin especialy in that dia. Sch.40 is better but as I remember it is only rated for 125 PSI
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If money isn't an issue (usually is though), you can use a CO2 shifter assy like:
http://www.biondoracing.com/CO2Bottles.shtml
This already has a regulator, is very small, and tested to a high pressure, and can be remotely activated.
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Your 3” stainless pipe should be OK. The nominal wall of sch 10 pipe is .120”. Assuming 30,000 psi yield strength of the material, the pressure to yield the wall would be about 2000 psi (sig=PD/2t).
It would be wise with this light wall to use caps, as you mention, or other externally engaging end fittings to keep the threads from dilating and going out of engagement. Assure the closures are also of comparable capacity. Then hydrotest, as mentioned above, to 2 or 3 times the operating pressure in a safe situation--secondary containment, under water, etc.
In stead of all that it may be worth the effort to do more looking for commercially available solutions--air tanks, air cylinders, hydraulic cylinders etc. You could probably get a commercial air cylinder assembled with caps on both ends (no rod or rod hole) which would have ports and such already included, i.e. Bimba.
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Look into using a hydraulic accumulator, they come in all sizes and use a bladder. I have seen them as small as 2" dia and 12" long. All are safe and high pressure housings.
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Your 3” stainless pipe should be OK. The nominal wall of sch 10 pipe is .120”. Assuming 30,000 psi yield strength of the material, the pressure to yield the wall would be about 2000 psi (sig=PD/2t).
It would be wise with this light wall to use caps, as you mention, or other externally engaging end fittings to keep the threads from dilating and going out of engagement. Assure the closures are also of comparable capacity. Then hydrotest, as mentioned above, to 2 or 3 times the operating pressure in a safe situation--secondary containment, under water, etc.
In stead of all that it may be worth the effort to do more looking for commercially available solutions--air tanks, air cylinders, hydraulic cylinders etc. You could probably get a commercial air cylinder assembled with caps on both ends (no rod or rod hole) which would have ports and such already included, i.e. Bimba.
IO, thank you for the info but I see I've left out one important piece of info. The caps I'm thinking of using would be butt-weld caps, not threaded. So I guess at that point the question becomes do I trust my welding enough to build a pressure vessel that will live in my car?
Knowing that the caps would be welded on, does this change your thinking?
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My thinking is that a properly welded formed cap would be preferred to a threaded connection, and is probably the best solution. However, just a solid piece welded in may be problematic, depending on its design and the nature of the weld. Still may be better than threaded, but depends. A formed cap will flex with the barrel, but a stiff plug will likely increase the localized loading on the weld where the barrel wants to "inflate" when loaded but the plug doesn't want to follow it. This doesn't preclude this method, but some thought should go into it. And successful proof testing covers a lot of sins.
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Nathan. (Google pressure vessels )there is a ton of information to he had. Includes a lot of calcs. on design and pressure testing etc.
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Aluminum fire extinguishers are pretty thin walled and are pressurized to 195 lbs for use. Maybe use one of them
Ron
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Nate, I have seen your welds, they are so nice I would have no qualms using a tank you built. Just test it for piece of mind. I like the stainless idea. :cheers:
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Nathan, there are a lot of medical oxygen bottles and airplane oxygen storage bottles that would work in your situation. Airplane bottles go out of date and must be replaced, inspection not allowed on most, the fire extinguisher is also a great idea...
Also a lot of compressors that have twin tube air tanks. Premade parts with fittings are often easier and less expensive than ones you make, be very careful when testing any tank
Check craigslist and ebay ...
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Nathan, if you're going to test the tank use hydro testing procedures. The tank is filled with water or another fluid and pressurized to a multiple of the pressure you're planning on using. In you're case I'd be tempted to just use hydraulic fluid and a hydraulic pump with a gauge. Because the fluid isn't compressed a failure doesn't result in a violent explosion. It still doesn't hurt to put the piece being tested inside a larger piece of pipe during the test and staying clear of the ends.
Pete
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McMaster-Carr has 1 gallon tanks 6" dia.
If I was an inspector I would want an ASME certified tank.
Custom/home made? Too risky.
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go to heavy truck parts dealer get a air tank for a air brake truck. that should work
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He has a space issue and thats part of the problem finding a air tank from a truck dealer. Worked in that business and most are 8" or more in Dia. Check with a welding supply company they have all sizes.
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Nate, In my industry, welds are routinely certified for 5000 PSI working pressure.
I don't see an issue with what you want to do- I might get them certified, but that's up to you.
That's low enough pressure, I think I'd just weld them up and go!
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How about the tank from one of those pancake air compressors they use in the construction trades?
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Nate is building a Model A sedan like I am building, space is a premium. I can see why he is looking at small tanks. Heck, my lakester has more room to fit parts than my Tudor!
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Hows about seeing if you scrap up one of those medical O2 tanks. They are only about 3-4" in dia. and goo to about 500lbs. Just throw'n bones out there.
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Hows about seeing if you scrap up one of those medical O2 tanks. They are only about 3-4" in dia. and goo to about 500lbs. Just throw'n bones out there.
http://www.ebay.com/itm/Medical-Oxygen-E-Cylinder-Tank-Steel-USED-/140690452299?pt=LH_DefaultDomain_0&hash=item20c1cdef4b (http://www.ebay.com/itm/Medical-Oxygen-E-Cylinder-Tank-Steel-USED-/140690452299?pt=LH_DefaultDomain_0&hash=item20c1cdef4b)
Buy it now: $9.95 + $6.00 shipping
Medical Oxygen "E" Cylinder Tank - Steel - USED
Please note that we have several THOUSAND of these available.
Specifications:
- Pressure rated @- 2015 PSI
- Height- 26 1/8"(top of steel cylinder), 29 1/4" (top of valve)
- diameter- 4"
- weight- 13 lbs
- capacity 25 cuft (oxygen)
:cheers:
Mike
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Nathan,
I modify hydraulic cylinders on a regular basis, cut them down & put new ends on them & all on 2500psi & up..
If you check a good hydraulic supply company you can buy tubing & blank ends in any size, just drill & tap them before you weld them in. If you can't find anything, go to baileynet.com, thats my suplier.
Sid.
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At 150psig along frame rail or cage/frame menber could do the trick as well. Seen a couple of build on this site that are using that method with success. More bones. :-D
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Hey guys, sorry for the delay. Made a promise to stay away from cars and computers this weekend. Celebrated my 9th anniversary with my wife. :-D
Okay, no particular order...
Stainless, good idea on re-purposing something like a portable air compressor tank. I actually had already considered this and found a couple of dead compressors on eBay for cheap. I sent some messages to the sellers with no response back so far. We'll see how that goes. Also, got your PM. Thanks for the offer. I just might take you up on it.
I could re-purpose an air cylinder (thanks for the link Mike) or scuba tank or even an old fire bottle. I guess my only concern is the fitting. I don't know a whole lot about these tanks but I think they all use a specific top fitting or valve that's unique to their particular application. I'd probably just cut it off and weld something on but I'd hate to compromise the integrity of the tank just to put a threaded NPT bung on the end of it. Nonetheless, a possibility.
Like Glen mentioned, an air tank from a truck is way too big. And like T-man said, this is going on my Model A and the spot I have available is very small.
Jim, good thinking on the pancake tank. This was also suggested to me by someone and I did my best to find a spot on the car where this might work but came up empty handed. The only spot I really have is be best suited for a long and skinny tank.
Pete, thanks for the advice on the hydro testing. Never knew how or why it was done. Did some research and now I know. When it comes time to test I'll definitely do this. Thanks!
Sid, thanks for the supplier connection. I'll hit them up if I go that route.
Captthund, thought about this as well and my frame rails are boxed but they have holes drilled in them to access the body mount hardware.
I think the good news here is that no one has really poo-poo'd the idea of making my own which is good. At least I know (or feel like) this is something I should be able to do fairly safely.
Looks like I have plenty of options... just need to pick one. Thanks again everyone.
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Nathan, Have you looked into any of the tanks made for paintball guns? They are small, light and good for I believe 1500 psi. Also, they are very cheap to buy. I found a 24 oz tank for less than $23.00 on the net. Sterling
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Every night I drain the air compressor tank and water blows out with the air. It collect in the bottom of a tank and it can corrode it. That is why it can be risky to buy a used air tank. A fellow does not know if it the water has been drained out of it on a frequent basis. It is good to have some extra wall thickness on a carbon steel tank. This allows for some corrosion without weakening the wall beyond acceptable limits.
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Nathan, here is the old AL firebottle I have...
Is anyone from Nathan's area going to the NW Reunion? Want to carry a 4x16 back?
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Nathan, here is the old AL firebottle I have...
Is anyone from Nathan's area going to the NW Reunion? Want to carry a 4x16 back?
Your local beverage supply should have [ or know were to get] CO2 bottles. That's were we got our air bottle to shift trans and they refill. About the same diameter as fire bottles but shorter for ours, but there are other sizes.
Also went to an air suspension place for quick disconnect fittings for lines.They might have everything you need.
JL222
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Lil bit of an update...
Did some research and some looking around and found that my local stainless supplier can get 4" pipe (4.5" od) and pipe caps in sch40 (.237" wall). Came across Barlow's formula and if my math is right, my compressed air tank shouldn't be a pipe bomb until I reach 3200 psi (shouldn't ever happen with any vehicle-mounted air compressor I've ever seen) and a working pressure of 300 psi... and that's with a safety factory of 10! The material alone will cost around $120 to make a 1-2 gallon tank and I could probably buy 2 or 3 cheapy eBay tanks for that price but it'll be kinda fun making my own custom stainless tank.
Thanks for all the help guys. Much appreciate.
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Nathan, no one will ever be able to accuse you of under building! :-D :-D :cheers:
Pete
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Oh no the b word now home land security is looking :-D
jl222 :cheers:
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I use a Viair air compressor to run my air shifter, provide air for my wastegate and cylinders that pull the pin to my limb restraints. Viair are expensive for 12v compressors.....but are really well made and have had zero problems in 5 years with this unit, and are designed for air bag suspension.
http://www.viaircorp.com/OnRoad/products.html
~JH
....and as far as bombs go....this is myself and some of my miscreant cousins at our cabin last month.....
http://www.youtube.com/watch?v=ZgYtYUTNUl0&list=UUCQeNEPLWsP3Z1V5WuVWzzw&index=1&feature=plcp