There are many drive options for truck-mounted air compressors. Many times, the choice will be dictated by other equipment already mounted on the truck.
Dan Kokot, executive vice president, Vanair explains that both hydraulic- and PTO-driven compressors are well proven. "By far, the cleanest application is a PTO-driven unit," he states. "There are no fluids or oils to deal with. There are no extra coolers for your hydraulic reservoir. You don't have all of the hoses and fittings. But there are applications where it will not work because of PTO restrictions. If the PTO port is taken to run hydraulics, most of the time they are running hydraulic air compressors, as well, because they already have it on the truck.
"There are efficiency differences between the various unit drives," notes Dan Hutchinson, product management specialist, VMAC. "Using a soft medium (hydraulic oil) reduces the overall power transmission efficiency, which increases the per-cfm costs. Hydraulic units are more flexible for placement onboard trucks, but use valuable cargo space. Truck engine-driven compressors reduce service and maintenance needs, require less insurance and don't need an extra engine. These compressors do not take any cargo space and are the most compact units without sacrificing power. PTO-driven compressors typically offer the highest cfm flow (185 cfm) without taking the cargo space."
"A direct drive runs more efficiently," says Tim Worman, product manager - commercial vehicles, Iowa Mold Tooling (IMT). "The hydraulic drive can produce the same amount of air as the direct drive, but the entire system would have to be sized to compensate for any efficiency losses."
If there is another piece of hydraulic equipment on the truck, chances are you will want to use the existing hydraulics to power the compressor. "A lot of mechanics trucks will right-size the crane flow to the compressor flow, so it is a matched system," says Todd Dufur, Doosan Infracore Portable Power. "The people who do that have a better performing system."