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Kopycinski's Brain - When You Need Air

Posted in How To on December 1, 2011
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Air. Compressed air. Do you need it and do you have it?

Flat tires, blown beads, bed toy tires, or camping air mattress. When you live the off-road life, it’s a good bet you need a mobile air supply for a variety of uses, including airing up after a day in the dirt.

There are numerous options for on board air sources can be made based on size, air flow capacity, and convenience. The popular options are electric air compressors, engine-driven compressors, and compressed CO2 bottles.

Electric air compressors have traditionally been the most popular option for onboard air sources. The smallest versions are compact units that plug into a 12-volt power outlet. These are relatively inexpensive, costing about $20 to $50, and are small enough to be stored easily. They draw relatively low amounts of power, but they tend to be slow. With small pumping capacity, these pumps may take five minutes or more to air up a tire. While they serve well for occasional use, these small pumps may overheat and seize if used for too long without allowing the pump to cool. Larger, more expensive electric air pumps ($150 to $500) may be semi-portable or designed to be permanently mounted. Such pumps can draw 10 to 50 amps from your battery, but air flow output is much higher than the little portable pumps described above.

Just as a home or shop compressor uses a separate motor to drive a compressor unit, so can your vehicle engine. Essentially, this involves mounting a second compressor unit (completely separate from your closed air-conditioning system) under the hood and finding a way to get belt drive to it. Engine-driven compressors have high flow output and can air up tires in a short time. With the addition of a small air storage tank, these compressors can easily run air tools. With their high output, engine-driven compressors tend to be one of the most expensive options, if purchased as a system. For those inclined to build their own on the cheap, it’s also possible to assemble a system using air conditioning compressor components with your own fabricated bracketry and control setup. However, these systems can be hard to fit in tight engine compartments.

A compressed liquid CO2 bottle can offer substantial compressed “air” volume. CO2 is stored as a liquid in the cylinder. Some portion of the liquid evaporates and builds pressure in the cylinder. It can then be released as a compressed gas through a regulator on the bottle. As more gas is released, additional liquid in the bottle turns to a gaseous state. Unlike compressed nitrogen bottles, CO2 bottles are far safer in transportation due to the liquid content, and they yield about three times the energy as compared to nitrogen.

The high pressure gas from the regulator is effective for reseating tire beads and offers the ability to air up tires rapidly. These tanks can also be plumbed to provide pressure for air lockers. A CO2 tank such as this is easily refilled at welding shops, but does contain a finite amount of CO2. It can, however, be weighed to determined how much remains in the bottle.

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