Portable Onboard Air 

A 12-volt air compressor should be a must have item for every work truck; portable air power for light-duty jobs 

By Peter D. DuPre

One of the must-have pieces of equipment needed on every contractor’s or construction worker’s pickup is a good air compressor because the jobsites, by the very nature of the work, are frequently remote and there’s seldom a shop air compressor handy.

Onboard, shop-style air compressors are great for service trucks or pickups where there’s a need for a lot of air to run big air tools over a long period of time.

But for those who don’t need all that air muscle and like to keep open bed space maximized, having a compressor powered by 12 volts or driven via an engine-run belt is a nice convenience accessory.

These compact, light-duty compressors can run smaller air tools for short periods of time off companion air tanks and power air horns, inflate air-suspension systems, air-up tires or blow dirt and dust off dirty filters.

INFLATOR OR COMPRESSOR

These 12-volt air compressors fall into two general categories: inflators and compressors.

An inflator is generally a small, 12-volt unit that plugs into the accessory socket and is designed for pumping up beach balls, air mattresses, small car tires and so on.

Generally these little inflators sell for less than $30 and often come with a built-in flashlight.

Most contractors will shy away from inflators and turn their attention to actual compressors, which have the ability to inflate a 35-inch truck tires, supply an auxiliary air storage (surge) tank, run a small impact wrench, or keep up with the demands of an air suspension.

Today’s better 12-volt compressors can supply 125 psi of air with enough air volume and duty-cycle time to run smaller air tools.

RATING COMPRESSORS

Air pressure (psi), air volume (cfm) and duty-cycle are key elements when shopping for your next portable or onboard 12-volt compressor.

The challenge buyers face when trying to compare compressors of this type is cfm varies with atmospheric pressure, temperature and even humidity; so rating a compressor can be complicated.

To rate compressors so they are all measured by the same standard, air compressor manufacturers rate their units in scfm, or standard cubic feet per minute.

The measurement standard, determined by the International Organization for Standardization (ISO) is taken as cfm (sea level) at 68 degrees Fahrenheit (F) and with a relative humidity of 36 percent.

(Note: The American Society of Mechanical Engineers (ASME) also sets standards for design and engineering of products and some manufacturers may use these standards, which are similar to those of the ISO.)

The scfm ratings are given at a specific air pressure. As an example, the popular Sears Craftsman 6-gallon 110-volt pancake compressor (#152160) is rated at 2.6scfm at 90psi and 3.5scfm at 40psi.

SCFM ratings rating go up as the pressure goes down. So make sure all your comparisons are at the same psi.