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.

Impact wrench - this one is made by Ingersoll Rand

Impact wrench – this one is made by Ingersoll Rand

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.Thanks,
Ken, good to hear from you.

Many questions, all of which are answered on the various pages of this site and it makes no sense to retype all that information again here, sorry.

Specifically though, if you wish to run an air tool continuously, then the compressor has to have the discharge capacity that the air tool demands and if you wish to run the air tool in a production facility, the compressor also have a duty cycle to withstand the demand of that frequent or continuous run time.

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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