----- Original Message -----
From: Larry Steckel <lorenzoscribe@hotmail.com>
To: <autox@autox.team.net>
Sent: Wednesday, November 26, 2003 9:57 AM
Subject: Air compressors
> Guys,
> I have been following the disucssion on air compressors from afar since my
> computer was slimed by a virus. It's all better now and I would like to
> throw my two cents into the discussion.
>
> First, the compressor industry follows a rule of 4 cfm per horsepower at
100
> psi. as a standard. That means that a 5 H.P. compressor should put out
> about 20 cfm at 100 psi.
>
> Second, the vast majority of the compressors available on the consumer
> market are massively over rated when comparing them to the above standard.
> Most "5 H.P." compressors are actually more like 2 H.P. maybe.
>
> Third, the buyer at Sears who purchased compressors told me once that
Sears
> did a study of its customers who purchased compressors from them. The
study
> showed that something over 90% of the customers used their compressors
> solely for filling up automobile and bicycle tires, and filling up various
> balls and swimming pools for the kids. Only a tiny minority used them for
> powering nail guns to do home improvement projects or for air tools for
car
> repairs.
>
> Fourth, the larger the tank on the compressor, the more air can be stored
> and the fewer times the pump has to cycle to keep the pressure up where
its
> supposed to be. The larger the tank the better.
>
> So, to pick a compressor for your needs, add up the cfm requirements for
> absolutely every air tool you own then add about 25% to give leeway for
the
> stuff you will end up buying and look for a compressor with that cfm
output
> at 100 psi.
>
> A 1/2 inch drive impact ratchet will burn up a lot of air. An air buffer
> will eat 20 cfm in a heartbeat. And once, during a test at a PPG Training
> Center, I saw a top of the line Sata HVLP spray gun use 21 cfm of air
while
> painting a test panel. Moral. Look at the box when you buy air tools.
>
> A small compressor will probably be more than adequate for tires and
> occasional work with air tools, but I suspect that most of us get a lot
more
> deeply involved than that in our projects. It would pay us to look around
> for a larger compressor that has the capacity to do the job we need.
>
> Oh yes. Remember to drain your air tanks regularly. Please use copper
> piping for your air system (white plastic from Home Despot is absolutely
> verbotten. It blows up!) and install the air distribution system in a way
> that keeps water out of your air drops. And at each of your drops make
> sure to add proper filters and regulators to your system to keep any water
> or oil that sneaks through the system out of all those expensive tools.
>
> Happy Thanksgiving to one and all.
>
> Larry Steckel
Typically the air output of small compressors is measured at the outlet port
into the atmosphere without any restrictions such as regulator, hose (those
coil up hoses and/or hoses >10' long cause a LOT of restriction to the
airflow), or are simply calculated by the displacement of the pump assuming
100% efficiency.
The motors are rated at the instant of startup, it is physically impossible
for 110V to drive an electric motor at anywhere near that HP continuously
(could some EE show the calculation, I think the actual max continuous is ~
3/4 HP)
A 110V compressor will drive an air ratchet, but it will not develop max
torque for more than a few seconds. The cheap ones sold as a kit at places
like Harbor Freight, are designed to use less air, at a much reduced torque.
If you want a real shop compressor buy a 220V dual staged twin cylinder belt
driven one. There is no such thing as a free lunch. Sorry.
|