As I've mentioned in earlier posts, I'm looking to buy a small
compressor for misc home use. I want the smallest usable unit I can get.
Besides low demand tasks, I would also like to occasionally use an
impact wrench for a seasonal tire rotation and possibly a die grinder
for stripping rust on a wrought iron railings. I've seen both tools
rated at around 4cfm @ 90psi.
I visited my local Lowes store and saw a DeWalt/Emglo 4 gal machine
rated at 4.1cfm @ 90psi. When I mentioned my intended uses to the sales
clerk, he laughed. He said I need *at least* a 15 gal tank to run either
What sort of intermittent use, if any, would a 4 gal unit provide? I
don't need Mr Goodwrench levels of performance. I'm just a guy in the
driveway doing 2 wheels at a time.
Do I truly need 15 gal+ before even considering using an impact wrench
when running. however, that's constant running.
it's supposed to not run more than 50% of the time, else you risk burning
out the motor. when it's off, it has to run using the stored tank. a 4 gal
tank won't run your wrench for very long, and you'll have to stop to let it
an impact wrench isn't a good example. it is usually only used for very
short bursts, which is ok to use a small tank for. a grinder will be used
for a long time. you don't want to be stopping every 30 seconds for a minute
or two to wait for the tank to catch up.
he's right. 15 might be too small for a grinder. i'd probably look at least
I use old oxygen tanks in series for heavy volume tasks like bead blasting.
All oiless compressors will crap out very soon if allowed to get hot i.e.
they run a lot. The rings are Teflon and do not last long when hot. Which
is exactly what your dinky compressor is going to do when connected to an
impact wrench. I installed an new patio cover this summer and used a 1/2
impact wrench to lag in the screws, 5/16 X 4.5 inches long. Even with my
extended tank capacity I could only do one screw at a time. I have an 15
gallon tank and I was running 120 psi.
A 4 gallon tank, lets see fill a tire, blow off the bench, brad nailers, and
staplers is all that I would try to run.
Check Harbor Freight, I have an friend that bought an 30 gallon unit for
about what I paid for my 15 gallon.
Gallons don't do the work, the output of the compressor does, but you find
small output compressors on small tanks.
An impact wrench is really a low air use tool. Generally it runs for a few
seconds and you are done with it so the compressor can catch up. Any small
pancake 4 gallon compressor will give you enough air to spin lug nuts off
the wheels of your car.
A die ginder, air drill, air rachet, or random orbit sander will kill you
for air use. I have run these tools of a 20 gallon genuine 2 HP compressor
but it would not keep up. I have a 60 gallon Porter Cable compressor that
almost keeps up with these tools. PC calls it a 7 HP, but it is really a 3
HP unit, runs on 240 volt only. It is close enough to keeping up for me.
I found that in the end I needed two compressors, a portable, that I can
drag around, and a large stationary for work in the shop.
You may want to buy a pancake for now, see how it works for you, then buy a
statioary compressor for the shop.
Ratings on air tools are the opposite of HP ratings on compressors! Tools
often are rated for less than their constant CFM, and compressors are rated
for max HP, not running HP.
My be that 4 CFM die grinder is over 10 CFM constant. In fact I have a
Granger catalog in front of me right now. Their die grinders are rated for a
25% duty cycle, on for 15 seconds, off for 45. The smallest grinder is rated
for 3 CFM, but in constant use it will suck up 12 CFM! Some of the grinders
are are over 20 CFM! So hook that up to your 4 gallon compressor and see how
many seconds it will run!
RTFM for the tools you want to use. Listed will be the SCFM requirements.
To use the tool at capacity you will need a compressor and tank that can
deliver the volume of air required. You might be able to get by with a
smaller unit but you will have to wait for the tank to recharge. I run a
6.0 CFM air chisel on my undersized compressor but if I use it for more than
short bursts I have to wait for the tank to refill. I think the tools you
mentioned have high pressure and flow. The wrench might meet the short
burst factor but the grinder is a sustained operation.
on 12/15/2004 8:51 PM Robert Barr said the following:
I guess the answer is both, but space is the biggest issue.
The other replys seem to reinforce why they make larger compressors. It
sounds like a 4 gal unit will drive low demand tools up to a homeowner
use of an impact wrench. That's about it.
That's why I asked.
If all you will be using a grinder for is wrought iron rails, I would be
looking at the wire brushes or the discs sold for drills (if you have a
I have an original Emglo twin which is a 4 gal., it will run a framing
nailer if I use 3/8" lines. It will run 2 roofing coil nailers all day
long. It will run an impact gun, fill your tires etc. Since it's portable,
it's ideal for taking on the job site. The big ole hunky 30 gal I have sure
doesn't see the action the little 4 gal does.
I have used drill attachments but the awkward size and constant kickback
is tiring. I thought the smaller angled grinder would be ideal. I still
do, but it doesn't sound like something I can use with a small compressor.
The 4 gal unit will still be useful, but I've lowered my expectations.
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