Impact wrench air consumption

by Ken
(Abbotsford, BC, Canada)

Hi Bill. Great site, just discovered it. I own a CH portable oil lubricated 8 gallon compressor, output is 3.7 cfm @90 psi. Bought it used when all I wanted was compressed air for automotive parts cleaning and the like. It happened to come with the crappy, 250 ft/lb impact wrench (rated at a relatively high 5.4 cfm) which is useful for tire removal and I do find myself using it for other things but it is limited. I now find myself looking for a more powerful wrench and find that most of the higher grade units demand even less cfm and deliver more torque than the one I have. My present wrench appears to be working at 100% capacity and, given the gap between the cfm rating of this tool and the compressor, it appears that one can get away with it in the case of intermittent use?? My theory is that the tool will receive it’s rated cfm and perform at 100 percent until tank pressure drops below 90 psi? Is this correct? Could you say that compressor rating seems to be a factor only when the pump kicks in and is expected to deliver air to a running tool (at which point you will likely be done using the tool for that cycle of usage)? Do you think I could get away with a better wrench and expect 100% efficiency when supplied by this compressor? I did upgrade to 3/8" hose some time ago but didn't change the stock 1/4" fittings at the time. I recently changed to 3/8” fittings which I would expect are necessary to obtain the full benefit of the 3/8” hose? Sorry for the wordy message but any information you might provide would be helpful.

Ken, good to hear from you.

Many questions, all of which are answered on the pages of this site.

Specifically, if you wish to run an air tool continuously, then the compressor has to have the discharge capacity that the air tool demands.

If you have a tank full of compressed air and a small air compressor, your air tool will run fine until the reservoir of pre-compressed air is used up. Then, since the air compressor cannot deliver air as fast as the air tool consumes it, the available pressure and flow will decrease to the point where the air tool cannot operate.

At that point you must stop using the tool and wait for the tank to refill.

If your air compressor is small and you want to use a higher demand air tool, you run the risk of burning out your compressor depending on it's duty cycle.

As far as I am concerned, the small air compressor is good for blowing off work benches and operating tools that have intermittent air use, such as brad nailers and the like.

If you need to work with a high demand air tool like the impact wrench, and you need to do a lot of work, you want to move up to a 3HP + air compressor, and if your livelihood depends on using air, at least a 5 HP with a 60 gallon tank.

See the sitemap page for links to pages with more specific info.



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Pressure needed for a die grinder rated at 4cfm @ 90 psi

by john everett
(westminster MD)

Craftsman 27 gallon air compressor (Photo:

Craftsman 27 gallon air compressor (Photo:

I bought a craftsman pro compesor rated at 5.8 cfm @ 90 psi My die grinder requirs 4cfm @ 90 psi ,I keep running out of air .

Should the compressor not be able to keep up with the use?

Compressor has a 27 gal tank

Any help would be greatly apperciated
John, when was the last time you got the mileage that the car EPA estimates said you would?

It's the same with air compressors, as far as I'm concerned.

If you are running an extension cord to the compressor, don't. That will be bleeding off motor power.

The compressor is dual voltage. If you can, and you are not, try running it with 240 volts instead of 120 volts.

Dial down the pressure to the die grinder if you can. That will help extend the air supply.

The specifications for this compressor, right from the Sears page are:

Drive Type: Belt Drive
Voltage: 120/240 volts
Horsepower: 1.9 hp
SCFM Delivery:
SCFM Delivery At 40 psi: 7.2 SCFM
SCFM Delivery At 90 psi: 5.8 SCFM
Compressor Tank Capacity: 27 gal.
Compressor Tank Pump Style: Oil Lube
Maximum Compressor psi: 150 psi
Compressor Tank Type: Vertical
Lubrication Type: Oil lubricated
Tank Style: Vertical
Type: Portable
Product Type: Air Compressors & Inflators

Despite those specs, sorry John... even though it says it is, I don't believe the compressor is big enough to run your die grinder satisfactorily.



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