So, if you’re ready to go pneumatic, here are some points you’ll want to
Wait, aren’t we giving up electricity for air? Yes, but your compressor needs
a power source. We’ll talk about the compressor in a moment, but first you
need to make sure your garage is equipped to handle the power demands. Some
compressors, especially large-capacity models, require a 220-volt power
supply. Others give you the option of running the compressor on 110 volts or
220 volts once you have made some minor wiring changes, which are typically
outlined in the owner’s manual.
What’s the difference? It comes down to the following electrical equation:
amps x volts = watts. Amps represent the volume of electric current, volts the
electromotive force driving the current, and watts the power generated by the
current. For a given wattage, as volts rise, amps drop.
Here’s an example: your new air compressor is rated at 3000 watts (check the
box, the directions, or the label on the compressor motor for the actual
number). If you plug it into a 110-volt outlet, it will draw a peak of 27
amps. That’s a lot of amps. It could be more electrical capacity than your
garage circuit is wired for. If you plug it into 220, it will draw only about
14 amps. That’s a big difference. It means smaller wires, less heat, and less
wear-and-tear on the electric motor.
Definitely consult with an electrician to determine your individual power
needs, but know that ensuring you have enough electrical capacity is the first
step in converting your garage to air.
This is the biggest single purchase, and the heart of the system, so pay
attention and shop around. (The photo at right shows a 5 hp/25 gallon
compressor that offers good sound shielding, easy to use air pressure
controls, a condensation drain cock, and the option of running at 110 volts or
220.) The air compressor breaks down to four basic components: a cylinder with
a piston that pumps air (larger compressors have two pistons), an electric
motor to drive the piston(s), a tank that serves as an air reservoir, and a
pressure regulator. Many compressors sold for home handyman use are oil-free,
meaning they do not require an oil reservoir that must be regularly topped up.
Professional-grade compressors, because they tend to work harder, depend on an
oiler. Longer life is the upside of an external lubrication source, but you
have to continually check and maintain the oil level.
Buying a compressor is like buying a computer; you want the best one you can
afford but you don’t want to overpay for capacity that you will never use.
Compressors range in price from a couple hundred dollars to a couple thousand
depending on the following factors:
Power. This is typically expressed in horsepower, but flagrant rounding
up by the compressor manufacturers is common. Do your own math: 1 horsepower
equals 746 Watts, so if the box claims 5 horsepower but only 3200 watts, you
know the horsepower rating is more like 4.3. The higher the horsepower, the
better able the compressor motor is to replenish the air tank. Larger tanks
(see the next point) require more powerful compressors to keep them filled.
Tank size. Compressor tanks can range from 5 gallons to 500. How much
do you need? It depends on what tools you will use. Small hand tools such as a
die grinder or an impact wrench consume relatively little air, while
constant-flow tools such as a paint gun or a bead-blast cabinet can leave a
smaller compressor breathless. In general, any compressor up to 25 gallons is
adequate to power hand tools, while 50-100 gallon tanks are the minimum
requirement for painting and blasting.
SCFM. This is the Standard Cubic Feet per Minute rating, often
expressed as CFM for short. CFM measures the volume of the flow of air
generated by the compressor at a given pressure (it varies as pressure rises
and falls, and also with temperature, so the Society of Automotive Engineers
uses SCFM, which fixes the pressure at 14.7 psi and temperature at 60ºF). In
other words, if someone measures how much air you blow out your nose during a
sneeze, that is your CFM, but not your SCFM. Volume matters to air-tool
operators because the higher the CFM rating (it generally rises with
horsepower and tank volume), the more work the compressor is able to do.