Used for everything from inflating tires to powering pneumatic tools, compressed air can be invaluable on many jobsites. It can also be invaluable if your applications allow you to mount the compressed air supply onto your mechanics truck to free up the hitch for towing other equipment, or increase mobility by eliminating the need to tow anything at all.
"You don't have to tow a portable unit to the jobsite," says Dan Kokot, vice president, Vanair. "You can use one truck to do it all and still meet all your air needs. It can improve your efficiencies."
There are numerous choices for onboard air compressors, ranging from under-hood or -deck models to above-deck units that are available in rotary screw- or reciprocating piston-type configurations driven by belts, hydraulics or PTOs.
Location, location, location
As in real estate, location can be an important consideration when determining which compressor is right for your truck.
Above-deck compressors — also known as utility skid mounts — are the most common, primarily because they're versatile. They come in a range of cfm/psi ratings, and are available in rotary screw and reciprocating piston types with hydraulic, gas or diesel drives. They are also less expensive than comparable under-hood or -deck models, and many can be moved to a new truck body if they outlive their initial host.
On the downside, you'll want to consider where the air compressor is mounted. "If it sits on top of the sidepacks, truck bed space remains free," says Tim Worman, product manager, Iowa Mold Tooling. "But if it has to sit in the bed, then you have to sacrifice space that could be used for carrying tools and other equipment."
Most also need to be readily exposed to outside air for cooling. "You can't necessarily put them in a cabinet all covered up because they would overheat," says Walter VanLaren, general sales manager, Service Trucks International. "They need to be up and out in the open where they can breathe and properly cool."
Space considerations are an advantage for under-hood or under-deck models.
Though less common than they were prior to today's sloped hoods and cramped engines, under-hood compressors still fill a need. These lightweight, compact models fit neatly under the hood to save space. For example, VMAC's 70-cfm unit weighs just 136 lbs. and is only 7 in. wide, 11 in. long and 6.5 in. high.
"If you like to have room in your truck bed, then an under-hood compressor is an option," says Mike Pettigrew, marketing manager, VMAC. "Except for the oil/air separator tank that mounts along the frame rail under the truck, the unit is completely hidden under the hood."
Since they are belt driven, under-hood models are also an option when hydraulic capacity is maxed out, or when hydraulics aren't plumbed into the vehicle. "Especially on smaller trucks, you might not have enough hydraulic power left to also run a compressor," says VanLaren.
For example, a Ford F-550 equipped with a hydraulically-driven crane and a generator/welder would not have sufficient excess hydraulic flow due to transmission torque limitations. "You might be forced to make a decision," says VanLaren. "Do you need to run all of those components at the same time, or can you switch from using one to another so you can share the flow? Or can you run the compressor by a different power source, namely the engine?"
When determining if an under-hood model is right for you, it's important to note they are available only as rotary screw models, and they are very truck specific. They are specially manufactured to mate with a particular engine and model of truck. So while it may outlive its host vehicle, it is unlikely to fit in the truck's replacement.
As with under-hood models, under-deck compressors free up payload space, plus some models run at about half the rpms for increased life. "These units will far outlive the chassis," says Kokot. "Then they can be moved to another truck."