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View Poll Results: What kind of Air Compressor do you have?
Oil-less less than 10 gal 6 2.06%
Oil-less 10-20 gal 17 5.84%
Oil-less over 30 gal 42 14.43%
Oiled less than 10 gal 5 1.72%
Oiled 10-20 gal 26 8.93%
Oiled 30-50 gal 40 13.75%
Oiled over 50 gal 150 51.55%
don't know 5 1.72%
Voters: 291. You may not vote on this poll

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  #46 (permalink)  
Old 03-14-2005, 01:43 PM
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Quote:
Originally Posted by oldred
I have witnessed this first hand and you can play with your slide rule all day and it will not change the fact that compressed air will expand violently if released suddenly. I have worked with air systems for over thirty years and I do have a good understanding of the physics involved here. You said that you saw a tank "blow" and it did squat, a loud pop and some hissing, since you are an engineer you should know the diffrence between "springing a leak and catastrophic falure" as happened in the two cases I related. I have seen a great many "leaks" happen due to rust or damage and a vast majority of the time a leak is all that does happen but when a tank really "blows" the results can be devastating! .
/\Exactly, for a chintzy comparision, poke a hole in a tire. It hisses and goes flat. Then, have a tire explode on ya, and it's downright violent.

I saw it happen on a big rig once, it made an alligator which landed in the windshield of a FoMoCo focus in the next lane.

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Old 03-14-2005, 05:59 PM
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Thats what I am talking about, that is if you release all that stored energy suddenly then you have an explosion on your hands kinda like this.
http://billsplanz.ieasysite.com/planez_016.htm
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Old 04-29-2005, 09:30 PM
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Quote:
Originally Posted by 454me
While an air tank can pop you really cant compare a 120-175psi air tank to a 2300 psi scuba tank. I have seen a wall plug go to ground in a house and it will pop a little and I have seen a 13,800 volt panel at work go to ground and it will open up 1/4 plate like a can opener.
True, scuba tanks are an extreme example. However, that first link in my post is pictures of a plain old 140psig home air compressor tank and it did a fair amount of damage too! Point is, even modestly compressed air in quantity holds a lethal amount of stored energy and must be treated with respect.
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Old 04-29-2005, 09:56 PM
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/\ever try that with propane? I always thought it'd be fun do dig a big hole in the middle of a field (10 feet deep or so, not too big diameter), set a tank down there, crack the valve, set a road flare, and run like hell.

Never tried it, but it'd be interesting.

variation: put a honda over the hole and play pop-a-honda. see who can pop the honda the farthest.
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Old 04-30-2005, 07:06 PM
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With compressed air tank explosions you are also dealing with metal fatigue associated from the metal tank's compression and decompression. There is a life cycle to the amount of times a pressure vessel can expand and contract. That is why most high pressure vessels have a finite life for service expectations. Such as with scuba tanks and gas cylinders which get inspected as a requirement.

I have heard and read varying opinions when it comes to air compressor tanks but it should also be noted that moisture from the compressed air can cause the tanks to fail even sooner due to internal corrosion.

Years ago there were a lot of IMPROVISED air tank explosions at drag racing events. People were using the portable containers to adjust air pressure in their tires and such. Afterwords there were a few Hot Rod Magazines with Articles about air pressure vessels concerning diasters and how to choose the right ones to be safe. The little portable air reserviors had a retirement DATE stamped on them but people would recycle these containers until they popped a hole or worse. So firmly believe that metal stress and corrosion can lead to explosive diasters with pressure vessels. There are numerous incidents to confirm that belief.

Heat and cold also have an effect on metal and plastic to contract and expand.

Some people use PVC pipe for air compressor lines. Often ignoring advice that it might not be safe and explodes like a fragmentary grenede when it does go off. Have to ask if PVC is okay for one application such as piping then why are the compressor companies relucant to make compressors with PVC air storage tanks? Just something to ponder. If it were feasible and safe then compressor companies would be using PVC to make tanks to save money(increase profits) and still be charging the same exact prices as the steel tank versions. Marketing could have a positive spin zone with the PVC not being effected by corrosion and probably even raise the prices. Where are the Air Compressors with the Certified PVC Tanks? I've yet to see one.

Incidently if you get a hole in your tank that is an excellent sign it is time to get a new one! Suggest you do not weld it up. Or live and learn. Compressed air has a lot of STORED ENERGY and should be respected.

As for wheels and big trucks there have been people killed by the 2 piece wheels coming apart while changing the tires on those style of wheels. That is a fact and the very reason there is a special cage to initally air up the tires after installation on those 2 piece styled wheels.
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Old 04-30-2005, 07:55 PM
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Timer- Very good points, especially the one about not welding a hole in a tank. If a hole pops in a tank then consider yourself lucky that's all that happened and don't even think of trying to repair it you very well could be making a bomb!
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Old 05-04-2005, 06:23 PM
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Quote:
Originally Posted by ChevelleSS_LS6
/\ever try that with propane? I always thought it'd be fun do dig a big hole in the middle of a field (10 feet deep or so, not too big diameter), set a tank down there, crack the valve, set a road flare, and run like hell.

Never tried it, but it'd be interesting.

variation: put a honda over the hole and play pop-a-honda. see who can pop the honda the farthest.
Actually, that would be a pretty safe operation until the tank was totally empty to the point that it sucked a little air back in and mixed it with the gas. There is no danger of explosion from a lit tank exhaust as long as there is a positive pressure inside the tank. that would function as a blow torch but not explode. A spark inside a 100% propane filled tank would just spark. No harm. Ditto for an air filled tank. However fill a tank w/ the right mix of gas and air and set off a spark inside and you will get the nuclear (or as George Bush wold say, "nucular") reaction you wanted!
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Old 05-04-2005, 07:44 PM
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Willys-I have seen pure oxygen from a torch tank mixed with both acetylene and propane by guys just horsing around (I would never do such a thing, no not me ) and it is amazing how big and loud an explosion you can get from even a small paper bag filled with this stuff. No joke, it is not something to play around with and one could easily get hurt or even killed since it only takes a small amount to do a LOT of damage!
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Old 05-04-2005, 09:05 PM
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Quote:
Originally Posted by oldred
Willys-I have seen pure oxygen from a torch tank mixed with both acetylene and propane by guys just horsing around (I would never do such a thing, no not me ) and it is amazing how big and loud an explosion you can get from even a small paper bag filled with this stuff. No joke, it is not something to play around with and one could easily get hurt or even killed since it only takes a small amount to do a LOT of damage!
Don't you remember chemistry class in HS? In the electrolysis of water experiment didn't you fill a BIG beeker with hydrogen/oxygen and set it off behind the prettiest girl in class? Oh and smear someone's class ring with mercury? And the best one of all, leave a big puddle of silver nitrate on someone's work table and when he thought it was a water spill put his hand in it and stained it black for a month? Of course not, neither did I!
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Old 05-17-2005, 05:49 PM
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via email, from Ken Stofen

This discussion has prompted a couple of emails from Ken Stofen, a retired inventor who worked on the design and construction of air compressor systems. I did some googling, and noticed that his name and email address matched up with some info on a couple of compressor-related sites. Here is the text of his two emails to me, with the attachments that he included. I'm assuming that he's unfamiliar with the board posting methods, but, considering the popularity of this thread, I thought I would post these for him.

----
Hi,

My name is Ken Stofen, I am an 83 year old inventor. I retired after 20 years designing, building and installing air compressor systems.

When I read about exploding air compressor receivers one engineer made the remark that what another reader thought he had seen could not happen.

When I saw a news release that a major air compressor company had recalled 458,000 portable air compressors because 11 receivers had exploded I decided to send this message to explain why I think those receivers exploded,

Many users are of the opinion that if you follow the manufactures directions and "drain the tank daily" that the receiver is dry inside when the liquid is drained out. What is more they think the liquid is water. Neither is true.

Absolutely pure water contains an equal number of hydrogen and hydroxyl ions, and is thus nominally neutral, although under certain circumstances it is capable of acting as a weak acid or a weak base. It is termed an amphoteric substance. Air, however, contains both oxygen and carbon dioxide. If air is dissolved in water, the carbon dioxide forms carbonic acid. The carbonic acid lowers the pH of the solution, and both the carbonic acid and the oxygen are corrosive. When air compressors are used out doors and often exposed to the hot sun or mounted in a hot boiler room the heat accelerates the corrosion end eventually they will explode.

The fact that it took about 10 - 15 years for 11 receivers to explode and that they were all from the southern states seems to bear out this theory. I think the reason the reason for the recall of 458,000 air compressors is because their engineers realized that all of them were a bomb waiting to explode

An engineer and I built a 5 HP tank mounted air compressor for my work shop and "processed" the compressed air with off the shelf components that enable it to deliver clean, dry and totally oil free compressed air and the inside of the receiver is always dry which should prevent it from exploding.

Best regards,

Ken Stofen

----
Regarding compressed air receivers exploding:

Thank you to the engineer who said, "oil in the tank with hot air and the right situation can cause a diesel effect and make a hugh explosion". I did not know that.

In the July 10, 1980 issue of Plant Engineering the editor wrote, "Air contains both oxygen and carbon dioxide. If air is dissolved in water, the carbon dioxide forms carbonic acid. The carbonic acid lowers the ph of the solution, and both the carbonic acid and the oxygen are corrosive."

Too many air cooled air compressors are installed in hot boiler rooms, or in a warehouse that is not air conditioned, or in direct sunlight on a back porch or in a hot attic. The hot receivers of these air compressors seems to accelerate the rate of corrosion caused by the carbonic acid and oxygen inside the receivers.

USGA Central Region Safety Newsletter reports, "Ingersoll-Rand is recalling 458,000 air compressors, "due to sudden tank failures."

Recalls and Product Safety News reports, Ingersoll Rand Company is recalling 458,000 Portable Air Compressors because the receivers on some of them, "unexpectedly ruptured."

These air compressors were sold between 1983 and 1991.

Years ago air cooled tank mounted air compressors were bolted to the floor so vibration wouldn't cause them to "walk around". I have seen foaming water leaking out of the welded seam at the top of the "foot" that was bolted to the floor.
I don't know who welded that foot on the bottom of that receiver but I do know receivers are pressure vessels and no one but a certified welder is supposed to weld anything on a receiver. I don't think that leak would cause the whole tank to explode but a new tank would be cheap insurance.

Customers move an air compressor into a hot boiler room simply because the air compressor is so noisy. Even with an automatic drain at the bottom of the receiver the inside of the receiver is always wet. Usually the automatic drain is shut off automatically when the air compressor is shut down at night. Then the receiver and all the pipes connected to it cool off and acidic oily-water condensate corrodes their insides every time the air compressor is shut down and cools off.

A compressor salesman told me that he knew of a vertical receiver fully charged with compressed air at 120 psig about 4 feet in diameter rusted out at the bottom and "took off" going right through the roof of the building like a rocket. I did the math. 4 foot diameter x 3.1416 = 12.56 square feet x 144 square inches = 1808 sq. inches x120 psig = 217,036 pounds of pressure (thrust). The probably could send the top of the tank through the roof.

In the November December 2001 issue of IR World Jack Petree wrote "Change Is in the Air." Jack interviewed Ted
Doheny, President of Air Solutions which is part of Ingersoll-Rand's Industrial Productivity Sector. Ted asked, "What if all compressed air systems could be supplied with the highest quality , oil-free instrument air supply, thus eliminating process concerns stemming from contaminated air?"

Engineer Leon Guntly and I built a system that will work on any new or existing make, model, type or horsepower size air compressor to enable lubricated air compressors to deliver clean, dry and totally oil-free compressed air. The condensate is crystal clear and can be drained to a sanitary sewer. The receiver is always dry.

I am attaching two recent articles from Hydraulics & Pneumatics Magazine. I hope these ideas will help your members avoid injury.

Best regards,

Ken Stofen

----
Attached Files
File Type: pdf 04.09-EditorPage.pdf (124.2 KB, 197 views)
File Type: pdf 05.03-AutomateAir.pdf (61.8 KB, 211 views)
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  #56 (permalink)  
Old 05-25-2005, 06:35 AM
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Thanks for passing that along, Jon. As soon as I figure out how to download those pdf attachments, I'll take a look (don't have the browser plugin for Adobe). He pretty well confirms what others have observed.

What about coating the inside of a tank with epoxy or polyester resin, as I read that somebody did in one of these compressor threads? That wouldn't affect the metal fatigue from the pressurization/depressurization cycles (remember the Hawaii airliner that lost its roof sometime in the 80s?), but it would seem to address the corrosion problem. Could that coating kind of equalize the life-spans of tanks in hot areas?

I don't have an air compressor system at the moment. My dinky "5HP" Campbell-Hausfield committed suicide by sending its little noisy piston through the sides of the compressor. I'm working on a Rube Goldberg-ian contraption to get air, after Oldred pointed me at some info. (Oldred, are you out there? Help!) Where do you buy ASME air tanks? The ones I find online are priced sky-high. Examples: Grainger lists a 60 gallon vertical for $685, Hanson lists a 60 gallon horizontal for $664. On the other hand, you can buy a complete system (with under-sized compressor) with a 60 gallon tank for about $400. What gives?

On hand: 6 cylinder compressor (50 CFM @ 90 PSI) originally powered by 15 HP diesel. 20 gallon tank, pressure switch, safety valve, regulator - salvaged from the dead dinky system. I've already experimented with driving the big compressor with the "5HP" motor. 2" pulley on the motor driving a 5" on a jackshaft with a 3" pulley that drives the 10" on the compressor. It runs until it reaches about 40 PSI, then the motor stalls and the circuit trips. Would a real 5HP motor (230V, 21A, 1740 RPM) be likely to get me to 90 PSI? That would be about $300.

(Sorry for the overlong post, but I've been researching this for ages and need help from more eyeballs, brains and experience).
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Old 05-25-2005, 08:53 AM
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The ASME boiler/pressure vessel code was created for this exact reason; poorly designed boilers and pressure vessels @ the start of the industrial revolution were taking out too much of the population when they blew! They are expensive 'cause they are built to anal retentive specifications. For example, a coded welding shop has a very short time to use up a can of welding rod before it must be discarded due to exposure to atmospheric degradation.

Coating the inside of vessels is problematic. If the coating isn't 100% integral, a holiday that exposes a point of steel will corrode at a rapid rate.

A strange thing happened to me with relation to corroded pressure vessels. W used to live in the country and we had our own water well. The well had a multi-stage electrical submersible pump that fed into a pressure vessel on the surface. The vessel had a rubber bladder that the water went into, protecting the steel from corrosion. The back-side of the bladder was charged with air pressure and the pressure in the air side of tank started and stopped the pump. One day the bladder broke and the pressure switch didn't work. I took the thing apart and was drying out the steel tank so I could install a new bladder. To speed up the process, I got out my trusty old air compressor and was using the blow gun attachment to blow out the inside and dry it faster. I was doing this for several minutes when I happened to touch the outside of the tank where I was directing the air stream on the inside and received a bad burn. The tank metal was almost red hot! I don't know the chemistry but the compressed air stream /water/rust/(organics?) combo was oxidizing something aggressively enough to melt steel!!
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Old 05-25-2005, 10:36 AM
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Quote:
Originally Posted by fast neutron
Does anyone on here have a 30gal. oil-less Craftsman compressor? I'm seriously thinking about one for my first compressor but not sure about their durability. I guess what I'm wondering is will this thing heat up and fry itself if I put a big air demand on it, i.e. greater than the 6.2 scfm @40psi advertised.

Thanks,

Matt
that;'s what I am using. It works fine but noisy as heck. I have it outside my garage on a concrete pad, with wiring and hose running thru the wall. I routinely use it for air chisel, all sizes on impact tools and drilling. The only thing that makes it work hard is the drill.
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Old 05-25-2005, 11:42 AM
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Quote:
Originally Posted by willys36@aol.com
The ASME boiler/pressure vessel code was created for this exact reason; poorly designed boilers and pressure vessels @ the start of the industrial revolution were taking out too much of the population when they blew! They are expensive 'cause they are built to anal retentive specifications. For example, a coded welding shop has a very short time to use up a can of welding rod before it must be discarded due to exposure to atmospheric degradation.
I understand the testing to specs, but that doesn't explain why a tank is more expensive than a complete system. It's even worse than a car body costing more than the car; these are standard tank sizes. Even the quantity discounts of compressor system manufacturers don't explain this wide a discrepancy. Somewhere there has to be a new ASME stamped tank for less than a complete system with an equivalent tank.
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Old 05-25-2005, 12:06 PM
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Quote:
Originally Posted by willys36@aol.com
A strange thing happened to me with relation to corroded pressure vessels. W used to live in the country and we had our own water well. The well had a multi-stage electrical submersible pump that fed into a pressure vessel on the surface. The vessel had a rubber bladder that the water went into, protecting the steel from corrosion. The back-side of the bladder was charged with air pressure and the pressure in the air side of tank started and stopped the pump. One day the bladder broke and the pressure switch didn't work. I took the thing apart and was drying out the steel tank so I could install a new bladder. To speed up the process, I got out my trusty old air compressor and was using the blow gun attachment to blow out the inside and dry it faster. I was doing this for several minutes when I happened to touch the outside of the tank where I was directing the air stream on the inside and received a bad burn. The tank metal was almost red hot! I don't know the chemistry but the compressed air stream /water/rust/(organics?) combo was oxidizing something aggressively enough to melt steel!!
now that's strange... you've been around here enough that I know you wouldn't bs us so if someone out there thinks willys is bsing ya just keep it to yourself please- don't hijack my thread!
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