Popular Woodworking 2002-04 № 127, страница 39

Popular Woodworking 2002-04 № 127, страница 39

ing a look at

some important compressor characteristics: horsepower, cycle time, compressor design, tank configuration and the machine's required routine maintenance.

Horsepower Rating

While compressors are typically rated by horsepower - between 3/4hp to 10 hp and up — what's really important is the volume of air they produce at a sustained pressure. The secret to selecting a compressor? Define what air

tools you'll be using now and in the future. As long as you find a compressor that can produce the volume of air you need, the horsepower is insignificant. Most air tools run at 90 psi (pounds per square inch) - a pressure every compressor is capable of producing. But what volume of air (measured in cubic feet per minute or cfm) does the tool need to operate properly? All air tools have varying cfm needs

(see the chart on air consumption on the next page). For instance, a narrow crown stapler used intermittently will need only 1 to 3 cfm. But a random-orbit sander, run continuously, will gulp 6 to 10 cubic feet of air per minute.

Cycle Time

Since most compressors are rated for a 50 percent "duty cycle" (which means the motor is supposed to be running no more than half the time the compressor is in use), running a tool like a sander non-stop will make the compressor run more often - maybe continuously, which will ruin the machine. To get around this, you'll need a compressor that produces a cfm higher than the highest rated tool you're planning on

by Rick Peters

Rick Peters is the author of "Air Tools: How to Choose, Use and Maintain Them" (Sterling Publications).

using. (If you're planning on running multiple tools simultaneously, add up the cfm requirements of the individual tools to get your target capacity.)

Recently, Porter-Cable and Craftsman introduced new lines of compressors that tackle the cfm/cycle time problem from a different angle. These new compressors use "high pressure technology" to provide longer, more continuous air to tools. To achieve this, they've tinkered with the cut-out and cut-in pressure points of the compressor. The cut-out pressure is the point where the compressor stops filling the tank; cut-in pressure is where it starts filling the tank. By raising both of these points, a larger "reserve" of air is available, which lets you work longer without risking reduced performance - a common problem with compressors that cut-in at 95 psi - only 5 psi above the minimum requirement formost air tools.

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