Cutaway View of Typical Air Cleaner

An air cleaner is simple in principle: a box with a squirrel- - dusty •

cage blower run by a small (fractional hp) electric motor. The blower ' AIR

pulls air through two or more filters, typically a pre fiIter and a pocket filter. The pre-filter protects the more expensive pocket filter from getting prematurely plugged with debris. The pocket filter captures the finest particles.

The amount of air that passes through an air cleaner is measured in cubic feet per minute (cfm).

wil! help capture the fugitive dust that escapes your other systems.

The Balance of Air Flow and Filtration

Effective air cleaning is a race against time. Once a dust particle becomes airborne, it's only a matter of time before it settles in your shop or lungs. To get the dust before it can settle, an air cleaner must circulate all the air in your shop every six minutes.

So, lots of airflow, measured in cubic feet per minute (cfm), is a good thing. But the cfm capacity of an air cleaner is only half the equation. You also need a top-notch filter to capture the fine dust. Only a few of the machines in our test successfully combined good cfm and good filtration (Fig. B).

Some machines have great filters but are less than robust in the cfm department (Fig. C). Others had lots of airflow but less efficient filters (Fig. D).

Testing Air Cleaners

Because of the technical expertise required to accurately test air filters, we took all the cleaners to Particle Tech, Inc., a professional testing lab in Minneapolis. Before the test we installed self-stick weather strip on the filter flanges of each Machine to reduce leaks (see "Air Cleaner Tips" page 81). Each machine was set in a sealed test chamber where a total of 80 grams of standardized test dust was introduced in 16-gram increments called "loadings." The standardized dust we used was made up of particles that ranged in size from 100 microns to less than 1 micron. Dust that got through the machines was captured and weighed to determine how much dust the air cleaner let through.

With each loading, cfm readings were also taken to track how the airflow degraded as the filter got dirty.


The "Blow Through" heading in the chart, page 82, tells you how many grams of the test dust got through each machine. It is a direct measure of filtration performance.

The blow through numbers are quite small, but keep in mind that this represents the smallest, most harmful particle sizes. So, a small difference in weight is actually a big difference in performance. For example, our worst performing machine let 68 times as much harmful dust through as our best performing machine. That's huge.

Manufacturers often use percentages to rate filter performance but this is misleading. In our test, the worst performer captured 91.5 percent of the dust and the best captured 99.875 percent. Long years of schooling have conditioned us to look on a 90 percent score as a great success. But that's just not the case with filtration.

Balancing Air Flow with Filter Efficiency

High CFM/ High-Efficiency Filter

The most effective air cleaners strike a balance between high airflow (cfm) and high-efficienc? filters. The higher the airflow, the faster your shop air will be cleaned. High-efficiency filters complete the equation, capturing almost all of the airborne dust sucked into the air cleaner.

Low CFM/ High-Efficiency Filter

Air cleaners with low cfm can't get all the dust before it settles out of the air. Even the best filter is useless if the blower fails to bring in enough air.

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