I know this question is a little off the board, but I figured someone here would know. My wife got me an air compressor for Christmas with an impact wrench and I'm having trouble getting the wrench to work right. My first air tool...

Compressor is 20 gallon, 5 hp and 6.5 SCFM @ 40 psi and 5.1 SCFM @ 90 psi. My impact wrench specs are Avg SCFM - 5.1 @ 90 psi (20% usage), continuous SCFM - 25.4 @ 90 psi (100% usage), max rpm is 7000, max torque is 250 ft lb and working torque is 60-200 ft lb.

I am having trouble taking off lug bolts, I figure I'm only getting about 60-70 ft lbs of torque. I know that my tank is small, I understand the basics but I'm not sure what 20% usage means. If my impact is max 250 ft lb does that mean at 20% usage I'm only going to get about 50 ft lb (20% of 250)? Sorry if this is a stupid question, but I can not figure out why I'm not getting any better torque. I always understood 20% usage to refer to time - you wouldn't be able to use the tool continually or for very long at a time before the pressure would drop and you would have to wait for the tank to recover. Thanks for the help.

Ryan

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RG Newell

1984 300D
1972 250
1986 560SL
1991 300CE