Basic Air Compressor Help! LPM? CFM?

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Old 02-07-10, 03:41 AM
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Basic Air Compressor Help! LPM? CFM?

Hi all,

I was given an air compressor as a gift and I am wondering if it will be able to run an 1/2" air ratchet/impact drill?

The air compressor is a Blackridge Air Compressor, 2HP, 77 LPM free air delivery and has a 21 litre tank.

When I convert 77 LPM to CFM, I get 2.72 CFM. If I were to get an air ratchet rated at 4 CFM, what would happen? The ratchet will not work at all? Work only for a short while? etc.

My primary use for the air compressor would be just a bit of engine bay cleaning and tyre pressures. I'm really hoping now I can use it with some air tools.
 
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Old 02-07-10, 04:08 AM
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Welcome to the forums!

I'm lost when it comes to metric values

The air ratchet will work, it's just a matter of how long. The same can be said of most air tools. The bigger the tank, the longer a small [cfm and hp] can keep up. When you use up the available cfm, the tool will work at a reduced speed and/or you'll need to wait on the air compressor to catch up.
 
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Old 02-07-10, 04:17 AM
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Thanks for the welcome and advice marksr!

Assuming the converter I used is correct and I only have 2.72 CFM at my disposal, how will a ratchet rated at 4 CFM perform on my air compressor?

More specifically, will it perform as it should like on a larger air compressor providing me a good amount of torque for several seconds before becoming useless?

I'm trying to weigh up whether or not it will be worth buying some basic air tools for the air compressor at all, or simply use it as a cleaning tool primarily.
 
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Old 02-07-10, 04:22 AM
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What size is the tank in gallons?
 
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Old 02-07-10, 04:24 AM
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Originally Posted by marksr View Post
What size is the tank in gallons?
The tank size is 5.5 gallons.
 
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Old 02-07-10, 04:35 AM
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It should work ok. Ratchets aren't typically run non stop so unless you run into a real stubborn bolt, I think it would do ok. Know any one that would loan you a few air tools for you to do a test run? My smallest air compressor has an 11 gallon tank [1hp] so I can't say with certainty how yours will work
I'm sure there will be others that will reply thru out the day with more info for you
 

Last edited by marksr; 02-07-10 at 06:18 AM. Reason: typo
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Old 02-07-10, 05:41 AM
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Not sure of your conversions, but it ain't right. With that much volume available, and the larger motor, you should be fine. I'm like Marksr, I failed metric conversions 101.
 
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Old 02-07-10, 09:00 AM
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Saw conversion of 1.25lpm = .044 cuft/minute; so it should be 26.6 cuft/min.
 
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Old 02-07-10, 12:35 PM
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You didn't give any dimensions of your gift compressor but I guarantee you that it isn't rated at 26 cubic feet per minute.

The conversion factor is one liter = 0.0353 cubic feet therefore 77 liters per minute would equal 77 times 0.0353 = 2.72 cubic feet per minute. Note that this is stated to be free air delivery which means at zero psi pressure or another way of stating the piston displacement of the compressor pump. For actual CFM at pressure you have to multiply by an efficiency factor which for a single-stage pump at 100 psi is going to be about 70% which would mean that your compressor pumps about 1.9 cubic feet per minute into the tank when the tank is at 100 psi.

About 20 or 30 years ago when home-shop compressors started hitting the market the manufacturers were using the term horsepower in an analogous method as Detroit did to automobiles. They rated the absolute maximum developed horsepower that could possibly be taken from the motor under laboratory conditions. This is, in my mind, is devious and dishonest. You will NEVER get a true 2 horsepower out of that motor in the real world and you'd probably be lucky to get even 3/4 horsepower on a good day.

Quite honestly, what you have is not much good for anything beyond filling tires in my opinion. Sure it will spin the ratchet or an impact wrench or cause an air hammer to run for maybe a half-minute but you will NOT be able to do any kind of serious work with that compressor. If you don't mind working for a minute (or less) and then waiting five minutes for the compressor to pump the tank back to pressure it might be okay for occasional use. It would probably be okay for a nail gun, especially a brad nailer, that you were using to install trim molding.
 
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Old 02-07-10, 12:55 PM
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I agree with furd...I really don't think it will run air tools very long. I have a DeWalt 4 gal that has specs of 4.5 CFM @ 100 PSI. It will run a air ratchet for about 10 sec before it slows down and loses all torque....and it won't break even the lightest bolt loose on air alone. My impact gun (250 lb torque) is pretty much a paperweight with it. It won't even loosen lugnuts that were put on with a torque wrench to 75lbs. Now...granted these aren't really very efficient air tools....I was just giving examples.

I'd call it a tire inflator and small nail gun compressor. It prob wouldn't run a framing nailer very well, at least not the way a framer uses one.

EDIT....ahhh I found some info. Looks like our OP is in Australia...and that compressor is sold by a place similar to Pep Boys or Harbor Freight. Includes a blaster, spray gun and inflator...and sells for about $100 AU.
 

Last edited by Gunguy45; 02-07-10 at 01:11 PM.
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Old 02-07-10, 03:46 PM
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Thanks all the advice guys.

I sort of had a gut feeling the compressor wasn't going to run the impact wrench, so I'll stop looking into that.

I won't be doing any nailing, framing, etc.

But I was really hoping it'll spin an air ratchet. Just so it only provides a good amount of torque for 5 seconds, or just enough to break lose a nut or bolt in a hard to reach spot, I'll be happy.

I've asked some mates and no one seems to have an air ratchet for me to experiment with, so I might take the dive and buy a cheap one to test.


Gunguy45: Yeah it was a $100 AUD package exactly as you described
 
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Old 02-07-10, 04:35 PM
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Air ratchets have essentially no break-away torque, maybe 40 to 50 foot-pounds if you're really lucky. They are for using manually to break the bolt or nut loose and then use power to run the bolt (or nut) out of a long thread. They also work well if the threads are slightly rusty, where it turns okay under power but too tight to move by hand alone.
 
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Old 02-07-10, 04:46 PM
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Originally Posted by furd View Post
Air ratchets have essentially no break-away torque, maybe 40 to 50 foot-pounds if you're really lucky. They are for using manually to break the bolt or nut loose and then use power to run the bolt (or nut) out of a long thread. They also work well if the threads are slightly rusty, where it turns okay under power but too tight to move by hand alone.
So if I had some bolts which should be torqued to 30 ft/lbs, and overtime have become a little more stubborn, an air ratchet would have trouble breaking it loose?
 
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Old 02-07-10, 05:11 PM
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I'm afraid so. When I first bought an air ratchet I was working in a power plant maintaining boilers. During the annual inspection I had to crawl inside and remove the nuts from 3/8 inch bolts. It was a cramped position and the bolts were somewhat rusty so using a box wrench was difficult. I often found nuts that the air power would not break loose and I had to use the air ratchet as a regular ratchet and pull strongly to break them free. After that they were still too tight on the threads to remove by my fingers but the air ratchet ran them off with no problem.
 
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Old 02-07-10, 06:23 PM
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The bolts I'll be working with hopefully won't be as tough as ones on the boiler you had to work with. It's more the lack of space to use a normal ratchet manually that has me interested in the air option.

Moving forward a bit, I've found something online, it's cheap, so its probably nasty:

1/2" Air Ratchet Wrench Heavy Duty Hand Air Tool

But it's got a rating of 77lpm which is exactly what my compressor is for, so I might grab that and have a play.

Also should I be using sockets made for air tools? Or will my normal sockets suffice?
 
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Old 02-07-10, 06:42 PM
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The air requirements for tools are also deceptive like the horsepower ratings for compressors.

For the ratchet it probably means that you will have the trigger pulled (using air) for about 10 seconds and then wait for 50 seconds before pulling the trigger (pressing the thumb button or whatever) again. This is called is the average air consumption per minute. The real consumption is many times the average but I suspect that you will be just fine.

You may use your regular sockets without worry.
 
 

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