Popular Woodworking 2002-04 № 127, страница 40

Popular Woodworking 2002-04 № 127, страница 40

Compressor Design

Here's another factor: When comparing compressors, you may find two with the same horsepower rating that yield widely different airflows. The reason is design: a single-stage or two-stage, with one piston or two. A single-stage compressor squeezes air in a single piston stroke to 25 to 125 psi. In a two-stage compressor, intermediate pressurized air is further compressed in a second cylinder to 100 to 250 psi. Since most air tools only require 90 to 100 psi to operate, a single-stage compressor will handle just about any job you can throw at it. Also, two-stage compressors tend to be more expensive and heavier than single-stage units and usually require 220-volt power.

Tank Configuration

There are four basic tank configurations to consider: single (10 to 60 gallons), twin (4 to 12 gallons), pancake (1 to 4 gallons)

and no tank at all. The larger the tank, the longer you can work at a desired pressure and flow rate -but at the cost of portability. I prefer twin tanks for small compressors because I can carry them with the tanks against my leg; this prevents accidental burns as the compressor heats up from use. I'd advise going with a conventional single tank for a larger compressor because they're well balanced and easy to move. Small, oil-free compressors are available sans tank, but they run continuously and have trouble delivering the air volume you'll need.

Recommendations

If you're planning on using high-cfm tools like framing nailers and random-orbit sanders, I recommend a large compressor (around 3 hp) with a 20- to 30-gallon tank and an output between 8-10 cfm. If you want to try your hand at spraying finishes, go with a midsize com-

AIR CONSUMPTION CHART

TOOL

Air chisel V drill

3/8" impact wrench Stapler Brad nailer Finish nailer Framing nailer Caulk gun Finish sander Random-orbit sander Sandblast gun Pressure washer Paint sprayer

pressor that can produce 5 to 6 cfm. If you won't be working with air-gobbling tools, a small portable compressor (around 11/2 hp) capable of producing 3 to 4 cfm with a 4- to 6-gallon tank will do the job. PW

CFM

4-6 4-6

3-4

1-3

2-4

4-7

4-10 1-2

5-9

6-10 2-3 2-5 1-5

PSI

70-90

70-90

70-90

70-90

70-90

70-90

70-90

5-70

70-90

70-90

30-90

40-60

10-70

MAINTAINING COMPRESSORS

Just like a car engine, oil-lubricated compressors need regular maintenance: Oil must be checked and topped off, and the filter and oil need to be periodically replaced. Despite this, oil-lubricated compressors have a reputation for performance.They often will run twice as long as an oil-free compressor between rebuilds. A typical, well-designed, oil-lubricated compressor will need a rebuild after 2,000 hours of use - that's three to four years if you use your compressor 10 hours a week.

Oil-free compressors, on the other hand, use non-metal piston rings, Teflon-coated parts and sealed bearings.Yes, they're maintenance-free -but only for a while. Since they don't use a lubricant, the internal parts of an oil-free compressor are constantly rubbing against each other. These compressors need rebuilds roughly twice as k

often as oil-lubricated compressors.

There's little to go wrong with a compressor as long as Bp^ you service it regularly-in particular, you need to religiously empty the compressor tank after every use (top). When air is pressurized, the moisture in the air collects inside the k ^ tank. If you don't empty it out, it'll rot your tank. It's also important to change the compressor oil and clean the filter H per the manufacturer instructions. Finally, make sure to test the pressure relief valve on a regular basis. This important ^^^^ safety device will eventually wear out under pressure. And when it does, you won't know until the tank explodes (no fun at all). Just pull the pin periodically to make sure it's functioning well. W

1 tit. ■ ,

Water tends to collect in your air compressor's tank.Unscrew the valve at the bottom of the tank to release the water.

40

Popular Woodworking April 2002

The pressure release valve is a fast way to empty your compressor of air.This valve also prevents the machine from exploding if over-pressurized.

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