Air Compressor Safety?

I don't have an air compressor yet, I know nothing about them, and
don't know anyone in person that owns one, but I was thinking about
getting one for running an impact wrench, air ratchet wrenches, and
occasional painting.
After some Google searches, I came across a few threads about air
compressor tanks exploding. It was sometimes caused by corrosion,
sometimes a bad relief valve, or bad pressure switch, or any
combination of the 3. I've also read that bad welds, a weak tank, or
other problems can contribute to a potentially fatal explosion.
I was originally going to buy the Harbor Freight 47065 "4-1/2 HP"
vertical compressor for about $150. It's oil lubed, so I thought it
would be a much better (and cheaper) alternative than picking up a
cheap oil-free compressor from Wal-mart. This would be for light
occasional use anyway, so I'm not too concerned about full cast iron
pumps or belt drive. My other alternative is to drop $400 on an oil
lubed Craftsman or Campbell-Hausfeld.
However, we all know Harbor Freight products are Made In China which
is not a country known for making high-quality products. If I buy a
cheap Chinese compressor, do I risk poor welds on the tank? A weak
tank made with poor grade iron? A pressure relief or pressure switch
that's likely to fail? If I'm risking my life by going cheap, I'd
definitely spend the extra money. If the HF compressor is perfectly
safe, then I'd rather buy it and save the money. Anyone have
experience with the HF compressor? I know compressor tank explosions
are few and far between, but I'm a very safety-oriented person.
Also, a quick question about compressors - when the compressor is not
being used, do most people leave the tank pressurized at all times and
the compressor plugged in, or do most people unplug them and bleed the
pressure out of the tank?
Thanks,
Shawn
Reply to
Shawn Lin
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Pressurized an unplugged.
Unplugged I don't care to have large autostart machinery set to run when I'm not home if not necessary.
Pressurized because it's handy to have an instant air supply for small jobs without waiting for the compressor to pressurize the tank.
Dick
Reply to
D.B.
I wouldn't worry about explosions. I imagine it could happen, but a tank would have to be very weak in order for it to happen catastrophically. These tanks aren't pressurized to 3000PSI like a SCUBA tank. It seems much more likely that you'd just have a leak. I had a blow off valve go out once and nothing drastic happened; just a very loud whistling sound as 150PSI bled down (though it scared the hell out of me...).
I've had cheap and expensive compressors and tanks (one that I've had for twenty years) and they're fine. Just put a dehumidifier inline if you can to keep the water out of the tank and tools and/or drain the tank periodically and you'll be fine.
Regards,
Peter
Reply to
Peter Grey
I believe all pressure vessels have to pass an ASME test in order to be marketed. Just how this fits into the handling sequence of a machine coming in from China, going through HF's warehouse, etc, I don't know.
Reply to
Leo Lichtman
On 9 Oct 2003 08:32:10 -0700, snipped-for-privacy@softhome.net (Shawn Lin) wrote something ......and in reply I say!:
The tank etc quality is probably watched fairly carefully by "the authorities". If you are worried about a tank exploding, then don't cross the road tomorrow.
However, your "4.5 HP" is interesting at $150. Even at 220V that will draw 15A.
Anyway, take no notice of HP. The only figure you are interested in is the CFM @ 90-100 PSI. If you can't get hold of that figure then make sure you can return the machine if it's not big enough. The compressor you are talking of _should_ be able to do about 4.5 * 2.75 CFM = 12CFM @ 90-100 PSI. Bet it can't. If it can for $150 then it's something special.
Don't try to "just sneak in" either. Compressors have all sorts of fudge in their figures, and so do tools. I have a "12CFM" compressor that cannot run a "5CFM" air Random Orbital Sander! In actual fact the compressor is about 7 CFM at 90 PSI (genuine 2.5 HP). I bought another one like it and between them they just about run the ROS. I was told that the ROS and like tools should use up to 20CFM comps to run hard and continuously. The tools are often rated at a strange rating, which should not be allowed IMO. It is based on occasional use, in a multi-user shop "So you can add them up to get the compressor size the shop will need"....yeah right....
Impact wrenches etc are better of course, because they are not often run continuously. But I have one, of quite reasonable quality. IT's good for about 450 ft-lb. If I am doing severl tough nuts, I need either both comps running, or I have to wait often.
****************************************************************************************** Those who can, do. Those who can't, teach. The rest sit around and make snide comments.
Nick White --- HEAD:Hertz Music Please remove ns from my header address to reply via email !!
Reply to
Old Nick
Keep the tank drained well - every time you use it, drain it. No water, no rust. (Well, almost.) If you like gadgets or have people using the system that can't be bothered to drain it manually, you can get automatic drain valves for stationary compressors that do the draining every time the motor cycles.
And I sincerely doubt that any ASME Inspectors have been within a thousand miles of any Harbor Fright factory... If you want the insurance on the shop building to stay in force, you'll need a compressor with an ASME certified tank, and the paperwork on file.
Consider any complex hand or power tools from Harbor Fright (including their air compressors) to be disposable. {If} ^w strike that... /When/ they break, getting replacement parts and service are going to be a problem, and it'll often be cheaper to throw it away and get another.
Although they are tempting to have around as a backup for your good tools, or as a "beater tool" - the one that gets used when working in a mud pit, at the edge of a cliff or on a boat on the water, where a tool can go "oops" and disappear forever.
I have their throwaway angle grinder with the grinding wheel for welding cleanup, and the good DeWalt with a knotted wire wheel for prep - if the HF grinder goes belly-up on me, I can start using the DeWalt for both and switching wheels between uses.
Use a Harbor Fright compressor for portable jobsite work where if it gets stolen or wrecked you're not out much, and get the good compressor for permanent install at your shop.
Moisture drained-off but still pressurized (you've already spent for the electricity to compress it) and turned off unless there's a reason to leave it on, like a hose left at the driveway for filling the bicycle and car tires.
IMPORTANT SAFETY NOTE: If you plumb a compressor permanently in the shop do NOT use any sort of PVC plastic pipe for the air lines. When it breaks, it grenades, and that can be just as deadly as it sounds if you're in the wrong place at the wrong time. Use copper pipe (soldered or brazed), black iron or galvanized pipe, with a piece of hose as a vibration isolator between the compressor and plumbing.
-->--
Reply to
Bruce L. Bergman
About a year ago, I bought a US made, ASME certified compressor made by Campbell Hausfeld and sold at Home Depot under their Husky brand. The top weld had two holes, one of which leaked. I would suggest paying more and getting Ingersoll Rand, Quincy, etc.
Reply to
AL
There are plastic pipes designed for air use but they only go to 1/2" which may not be large enough for a big comp. They are reliable though and the push fittings are quick to install.
John
Reply to
John Manders
There are larger plastic pipes that are rated for air use. They're green plastic (I think ABS.) The fittings are glued on with a solvent cement. One brand name is Chem-Air. They are expensive.
-- Steve
Reply to
Steve Dunbar
How about UL inspectors? I don't know about HF, but I noticed that Homier's compressors don't have UL markings on them. One of them had a little tag warning the user to unplug it when not in use to reduce the risk of fire.
A compressor in a commercial setting needs to have a permit from the state boiler inspectors, and be re-inspected periodically. The requirements will vary from state to state.
Reply to
Steve Dunbar
Thanks for the reply! Automatic drain is a great idea! I tend to be forgetful so this will come in handy (I know I have scared the wife several times by accidentally leaving the soldering iron plugged in overnight).
Exactly my concern. There's no mention of ASME anywhere in the Harbor Freight ad for this compressor. The $400 Sears portable compressor I was looking at (the cheapest oil lubed portable vertical compressor they offer) does have an ASME tank.
[snip]
That's true, and I realize that. I just want a portable compressor for light use for the next 3-5 years. After that, I plan to have a new house built and a larger, higher quality compressor installed remotely in its own room. A friend of mine is doing just that in his house with air plumbed to both the garage and workshop, it's a pretty slick setup. The compressor I get now only HAS to last 3-5 years, and I'll probably only use it a few times a year to run an impact, inflate tires, light painting, blowing out the inground sprinkler system, etc. The real work (like painting whole cars) can wait till I can get moved into the new house and have a real compressor.
Thanks for the warning, I read about that too. The compressor I get now will just be a portable so it won't be permanently plumbed. However, when I do buy a permanent compressor, I'll use copper. That's also what my friend used, so he should be able to give me some good pointers when I get to that point.
Thanks again,
Shawn
Reply to
Shawn Lin
There is a very graphic reminder of the power of compressed air on
formatting link
bottom left from memory. Don't get complacent about compressed air.
Glenn
Reply to
Glenn Cramond
see post in "air compressors??" thread about new "cheap" compressors.
RE exploding - not likely with corrosion - it will cause a hole and air will escape - exploding requires a sudden release, and unless the welds are bad or something, that won't happen.
summary of suggestion re compressors - look ONLY at CFM - for an impact wrench where you don't run it long, the tank size is important, but for spraying or sand blasting, etc, you need steady CFM - and 2 CFM is not enough - you need 8 to 10 CFM minimum at 60 PSI, better to have 15 at 120 or above
Reply to
william_b_noble
I bought a cheap ROS and returned it when I discovered my air compressor could not keep up with it. I bought a better quality/more expensive ROS and it seems to consume much less air.
cs
Reply to
Charles A. Sherwood
On 14 Oct 2003 20:53:19 GMT, snipped-for-privacy@w-sherwood.ih.lucent.com (Charles A. Sherwood) wrote something ......and in reply I say!:
Yes. I think the "tolerances" become huge gaps in the cheaper stuff. My main target with that post is people who are buying "on a budget". The problem is, the ROS says 5CFM, 90 PSI, and it's complete BS.
****************************************************************************************** Whenever you have to prove to yourself that you are not something, you probably are.
Nick White --- HEAD:Hertz Music Please remove ns from my header address to reply via email !!
Reply to
Old Nick
I know nothing about the area where you are, but frequently the larger tool retailers around here will have factory refurbs, demo models or returns for sale at about 50% off new price. I've had a Rocket oil-less, which is a Coleman refurb, with an 11 gal. horizontal tank for about 7 years now, it's been worked hard and is still going strong. It's rated at 4.5 cu/min at 90 psi, it runs everything I've got fairly well except for the DA sander. That drains the tank in a couple of minutes. I needed something that was portable and wouldn't spill oil if it tipped over in the back of the car. There's some definite limits on what it will do, but it runs off regular 120 v. which is another plus given the rental place I'm living in. The oil-less feature is good for spray painting, too, no possibility of oil contamination. This area is usually dry enough that not much water accumulates, but I regularly blow the tank down anyway. The water trap bowl just accumulates dust, not moisture. I think it cost in the neighborhood of $125 and I've gotten my use out of it, spray-painted the top of the van, 4 VW fenders, trunk, hatch and two doors, any amount of shellac on video racks. If you get one of those small touch-up guns, the compressor can keep up. You just have to be selective on the tools you do buy. The only other downside is the noise, the motor runs at double the speed of a regular belt-drive compressor and it makes a racket in an enclosed area.
Because of the noise, I shut the thing off when not in use, neighbors wouldn't appreciate it starting up in the middle of the night...
The only leaks I've had were because the drain petcock got damaged when the unit was moved around. About a $.79 fix, now I keep a couple on hand and it hasn't happened again. My brother-in-law's Craftsman has a pinhole leak, he's in a swamp in Indiana and never drains the tank. Last time I used it, it was half full of water and we had to wait about 45 minutes for it to drain out. It's a horizontal tank unit, the drain petcock is placed perfectly for the shed's door sill to nail it as it's wheeled through the door. Something to look out for on portable units.
There's several grades of compressors. Cheapest is plated alloy cylinders, ala chainsaw engines, the cheapy oil-less compressors have these. Up from there is the alloy block with iron sleeves. Top of the line is the full cast iron compressor. The lower two grades now can come as direct drive, I've never seen a direct drive compressor that's all cast iron and oil-lubed. Most of the popularly priced oil-lubed compressors are alloy block with sleeves. The guy at the local Tool King store yesterday had a Porter Cable vertical direct drive airless that he claimed was as quiet as a belt drive, I didn't hear it run, though. Had the alloy block with iron sleeve, about $400. 20-something gallon tank, was wheelable. I looked at that HF unit on sale this weekend, I passed.
Stan
Reply to
Stan Schaefer

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