Choosing a truck-mounted compressor can be confusing. There are under-hood, under-deck and above-deck units. There are both rotary screw and reciprocating piston pump airends, and the units can be driven by a belt, PTO, hydraulic motor and internal combustion engine. In addition, there have been advancements in design. Yet, the most important place to start is still with your air demands.
Size it right
"The most important consideration to understand when determining the right truck-mounted compressor is the application in which it will be used," says Tim Worman, product manager - commercial vehicles, Iowa Mold Tooling (IMT). "What types of tools will you be running and how much air and pressure do you need to run them? Also, you need to consider how many tools you will be running and how often air will be needed. If air is needed constantly, then a rotary screw compressor would be the best option."
Start by asking yourself what you will be doing with the compressor to ensure you won't overwork it. "For example, if you're running a 1-in. impact wrench 80% of the time, you would be overworking a 35-cfm compressor," notes Worman. "Sure you could run it that way, but it would be inefficient, because you would cycle the compressor more and would waste time while the air tank is refilling. In that application, you would probably want to have an air compressor that has a higher cfm rating for the job at hand."
But undersizing is usually not the problem. "If there is a common mistake, customers tend to oversize the unit," says Dan Kokot, executive vice president, Vanair. Most pneumatic tools are rated at 90 to 110 psi. Delivering higher pressures to the tools than required will only shorten tool life.
Oversizing can also impact the compressor's longevity. "If you buy a compressor that is too large, you actually don't work it hard enough," says Chris Lamb, truck-mounted equipment product support & training, Doosan Infracore Portable Power. "If it is never really loaded, you don't build up enough heat to evaporate the moisture. It can shorten the life cycle."
According to Todd Dufur, strategic accounts, Doosan Infracore Portable Power, this inability to achieve the desired operating cycle can also lead to trouble with the air/oil separation system that removes the compressor oil (used to lubricate the system) from the compressed air. "With the compressor, you really want to have good separation," he states. "If you are not using it, you are going to have poor separation, or oily air."
Take a close look at the tools you use to determine the proper air flow and pressure required, says Dan Hutchinson, product management specialist, VMAC. "Also important is the duty cycle needed. You can plan for 100% duty cycle for rotary screw compressors, but only 40% to 80% for piston compressors," he explains.
The operating environment plays a role, as well. "The harsher the environment (temperature, contamination), the more important it is that the system be protected," says Hutchinson. Measure the impact of the system's size and weight against the need to maximize the amount of cargo capacity, as well as the size of the truck and feasibility of a compressor installation on that platform. "The other requirements of the truck - such as the need for hydraulics - must also be considered."
"With an under-hood or under-deck air compressor system, the most significant advantage is that it frees up deck space," says Hutchinson. "Typically, there is also a reduction in the weight of the compressor, which translates into fuel savings and environmental benefits.
"The most notable drawback for under-hood compressors - a facet that most customers are unaware of - is that the research and development process for these compressors must be started much earlier because of the complexity in design," he continues. "Manufacturers like VMAC work with the OEM truck manufacturers long before truck prototypes are even produced in order to ensure the equipment is available as the truck models come to market."