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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.
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.
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.
If all the compressor manufactures and marketers listed both ratings on their products you could make good comparisons. But they don’t.
Instead, they use whichever is the biggest number (cfm or scfm) in their advertisements and promotional literature. So unless you have each compressor’s technical specs it’s difficult to shop apples-to-apples on flow capacity alone.
To make a good comparison you have to use scfm, cfm and psi ratings to get a good idea of what the compressor can do – and how it compares to another.
Another factor in rating compressors is the duty cycle. This rating reflects the percentage of time a compressor can run at 100-percent capacity at a set psi before it has to stop to cool down. Normally that number is based on a 10-minute run period, usually 100 psi at 72 degrees F.
This is an important measurement because light-duty air compressors don’t have the volume of a stationary compressor with a built-in air tank. So the 12-volt compressor will run until the demand for air stops – or it gets too hot to function properly. Hence, the higher the duty-cycle rating, the better the quality and efficiency of the compressor.
For example, an air compressor with a 33-percent duty cycle can run for three minutes and 20 seconds and then has to stop for 6 minutes 40 seconds minutes before is can efficiently pump again.
Running a compressor for longer periods of time than its duty cycle reduces its efficiency to compress air and, if operated repeatedly in this manner, will greatly reduce the compressor’s life.
If you plan on using a 12-volt air compressor for more than pumping up the occasional tire or running an air wrench for extremely short bursts, you’ll need to install an air (surge) tank in which to store compressed air.
Surge tanks serve as that down-time buffer so the reservoir of air will meet short-term, high- demand usage while the compressor cools down. The size of the tank determines how long the air tool can run before the compressor kicks back on.
In addition, the surge tank eliminates the compressor pulsations and helps separate out water, particularly if the tank is of sufficient size for the air to cool quickly once the tank shuts off. (Installing an in-line water filter may also be a good idea, particularly if you are in an area of high humidity.)
While it is possible to mathematically figure out what tank size you need, it is generally smarter and easier to consult the compressor manufacturer, since virtually all of them sell air tanks and pressure cut off switches designed to work with their particular unit.
Most contractors will find a two-gallon surge tank will work well quickly filling a flat tire or running a small air wrench for short bursts to remove lug nuts. A tank of this size fits behind a seat or in the toolbox and is easily portable.
Onboard air tanks vary from ½ to 12 gallons and are generally matched by the manufacturer with specific compressors, depending upon workload.
While there are a number of brands and models of portable and onboard 12-volt air compressors, there is no one “right” unit for on-the-job use. The purchase decision depends upon what you see the main uses for it once you leave the shop.
Taking duty cycle, air volume and pressure into consideration will help determine if the compressor you have your eyes on can supply the amount of air needed to inflate those “E”-rated tires on your fleet’s pickups as well as those on your trailers and smaller equipment.
If you are also planning to use the unit for running air tools, plan on installing a surge tank – or at least having a portable tank in the pickup so there’s enough volume available to handle the task without burning up the compressor.
It’s also good to fit your compressor or tank with an adjustable regulator on it so you can turn down the maximum setting when using air tools.
The bottom line when choosing an on-board 12-volt air compressor is to buy the one that can handle the biggest task you commonly face in the field, be it airing up a low tire on a job or filling an air mattress when you go camping.
Just keep this thought in mind: Buying a portable 12-volt air compressor is like buying a winch where it’s better to have too much muscle than too little.
If you need a permanent under-hood air compressor, then the belt-driven offerings from ExtremeAir, sold under the ExtremeFlow brand, is a good solution. They come in either V-belt or serpentine-belt configurations.
Both compressors deliver 8 cfm at 100 psi with a maximum rating of 200 psi. ExtremeFlow’s compressors ($415) feature a serviceable Zerk fitting for lubrication and use high- temperature synthetic grease.
These powerful compressors will fill bigger tires and run air tools with ease. The compact size makes for easy installation in just about any pickup’s engine compartment. ExtremeFlow: 866-447-7711; extremeoutback.com.
When 12V air power doesn’t cut it, but compactness is still a priority, another good choice is the VMAC Underhood 70-G belt-driven compressor.
VMAC has 100-percent duty cycle underhood compressors rated at 70 and 150 cfm with a maximum of 175 psi. Best of all, with their Intelligent Digital Controls, the VMAC 70-G air compressor system will turn the truck off when air is not being used and then start it up when air is needed again.
An adjustable automatic engine control and digital setup on the LCD control box display operate the system, which currently available for the Ford 6.7L Powerstroke Diesel. Additional applications will be available soon. The unit comes with a two-year warranty and will fit most popular work trucks. VMAC: 800-738-8622; vmacair.com.
These twin on-board compressor kits (12V or 24V) are fast and compact, yet deliver high-volume for operating air-powered tools, air lockers and air suspensions, filling large tires and other jobsite usage. ARB’s CKMTA12 ($545) are sealed against water and dust, and the 6.16-cfm free-flow rating is the most of any 12V compressor of its size on the market. The pressure switch-controlled air manifold system regulates pressure between 135psi and 150psi. A heavy-duty, high-performance portable version of the Twin On-Board Compressor (model #CKMTP12/ $875), mounted in an impact-resistant polymer case with water-tight seal, features an integral aluminum air tank and pressure switch, 12V power leads with battery clamps, 20-foot-long air hose and an air blow gun.
ARB USA: 425-264-1391; arbusa.com.
When it comes to fast tire fill, the Air Lift QuickShot is a pressure-driven compressor system, with its two-gallon surge tank, is a strong contender. QuickShot features an in-dash control panel for easy monitoring, and delivers .81 cfm with a 33-percent duty cycle at 100psi. The QuickShot ($647) is available as either a single gauge/single path or single gauge/double needle/dual path system. It comes with a two-year warranty and a 60-day no questions asked money-back guarantee.
Air Lift: 800-248-0892; airliftcompany.com.
ExtremeAir offers 11 different compressors, the most popular of which is the ExtremeAire Magnum ($565). This sealed unit features a 1.5hp motor with a continuous-duty fan-cooled motor that can be mounted at any angle or orientation. The Magnum delivers 6 cfm free-flow and 2.6 cfm at 100 psi. The Magnum features excellent filtering, stainless steel hardware, heat dissipation cylinder coating and powder-coated filter housing and fan shroud. Sealed bearings mean no servicing or lubrication is necessary. ExtremeAir also offers portable versions of all their compressor models that have the same performance specifications as the hard-mounted units. The portables come in a case with pressure gauge, 33-foot coiled air hose, 10-foot long jumper cables and a LED flashlight.
ExtremeAir: 866-447-7711; extremeoutback.com.
The HP325 Series air compressors ($170-up) from Pacbrake have a 33-percent duty cycle and are rated at 1.2 cfm at 100 psi. The HP series is offered in both 12V (model # HP10142) and 24V models (model # HP10151). These ¼hp compressors feature oil-less design with sealed bearings, PTFE piston ring, copper wire wound permanent magnet motor and a hard anodized aluminum sleeve and are intended for light- to medium-duty use. Complete kits ($260) are also available, consisting of air line, regulator, wiring and electrical hookups. Pacbrake also offers both ½-gallon and 2 ½-gallon surge tanks.
Pacbrake: 800-663-0096; pacbrake.com.
Designed to supply 150 psi, the Maradyne Junior Jet 150 inflator is ideal for those want an occasional use, portable unit for filling tires. This inflator features a low-noise, high-airflow design to quickly deliver air through a 27-inch air hose equipped with a quick-release thumb twist valve connector. The Maradyne Junior Jet 150 ($90), which comes in a carry case, has an average fill rate of 7 psi/minute on a 16-inch tire. Other features include a built-in air pressure gauge rated at 0 to 150 psi and flashlight, which adds safety during nighttime use. A 9-foot-long power cord plugs into the vehicle’s accessory socket.
Maradyne: 800-435-7953; maradyneHP.com.
If you are looking for 12/24V onboard air with the muscle of a shop compressor, the XD4000 Series compressors from Oasis Manufacturing are designed for commercial, military, off-road vehicle and service truck use. The Oasis XD4000 features a 2.2hp forced-air motor and compressor cooling system resulting in a 100-percent duty-cycle at 200psi and a service interval of 50 hours. The XD4000 ($1,700) delivers 200 psi, 8 cfm at 100psi, which is powerful enough to run a ½-inch drive impact wrench without the need to install a surge tank. Oasis claims they have been tested and proven to be the fastest, most powerful on-board 12/24V compressor available, matching or exceeding the performance of a shop air compressor.
Oasis Manufacturing: 888-966-2747; oasismfg.com.
A twist in onboard air power is the Smittybilt CompAir Trail Tank. CompAir system ($250) isn’t a compressor, but a high-pressure 10-pound CO2 bottle (must be filled at a commercial compressed gas facility) that allows you to carry compressed air source with you to inflate tires or run small air tools without a compressor. The Smittybilt CompAir kit comes with an adjustable integrated regulator (250 psi max) and is capable of pumping a massive 32 cfm of compressed gas, allowing you to inflate up to 10 35-inch tires in just 56 seconds each. The compressed gas tank also delivers plenty of “air” for operating light-duty air tools such as wrenches and drills. It comes standard with an air chuck, 25-foot hose and heavy duty carry bag.
Smittybilt: 888-717-5797; smittybilt.com.
Need to step up in portable air power? The heavy-duty Pacbrake HP625 Series air compressors, available in 12V ($298) and 24V ($333) models, feature 100-percent duty cycle and are at 3.4 cfm. These ¾hp compressors are offered in both vertical and horizontal head configurations for easier mounting. The oil-less design, sealed bearings, and cast steel cylinder with a hard anodized aluminum sleeve ensure long life. The HP625 series compressors require the use of an unloader assembly (part # HP10116), for use with an air tank. Installation kits designed to hook up a 2 1/2- or 5-gallon air tank are available as well.
Pacbrake: 800-663-0096; www.pacbrake.com.
If the ability to inflate tires quickly is all that’s needed the Smittybilt HD ($150) compressor may be just the ticket. It will inflate a 35-inch tire about 50-percent faster than other portables and rated at 5.65 cfm. Power is supplied directly from the vehicle battery via alligator clips and the 12V compressor is rated up to 150 psi with a maximum continuous cycle time of 40 minutes (40 psi at 750F internal temperature). Other features include a quick-release 24-foot coil hose, easy twist brass inflator fittings, 10-foot power cord, nylon storage bag and anti-vibration rubber feet. The unit can also be mounted and hard wired into the vehicle.
Smittybilt: 888-717-5797; smittybilt.com.
While its original design was intended for RV use, the 2.54-cfm, 150-psi Viair 400P-RV ($300) is a gearless, direct-drive compressor well suited for contractors and landscapers. It’s sealed against moisture and dust, will inflate a 35×12.5-inch tire from zero to 30 psi in less than five minutes, and has a 33 percent percent duty cycle (at 100 psi). The 400P-RV kit, which includes 58 feet of coil hose, is powered via jumper cable clamps and comes with a 45-degree two-way quick connect open-ended air chuck, a 90-degree twist-on on open-ended inflator/deflator, a billet sand tray for stabilization and a sturdy canvas stowage bag with side pockets for tools.
Viair Corporation: 949-585-0011; viaircorp.com.
The Viair Heavy Duty 10005 compressor ($380) is a gearless, direct-drive compressor with a 33-percent percent duty cycle (100 psi), maximum 150 psi capability and 2.54 cfm rating. It’s moisture and dust resistant. It offers contractors a pre-packaged compressed air system complete with wiring harness, dash-panel gauge with on/off switch, and a 2.5-gallon surge tank with safety valve and drain cock. Other features include a pressure switch with relay (110 psi on/150 psi off) and a 35-foot coiled air hose. Viair tests indicate the unit will inflate a 35×12.5-inch tire from zero to 30 psi in less than five minutes. That’s good for a lot of smaller jobs.
Viair Corporation: 949-585-0011; viaircorp.com.