The adage, “A painter’s house always needs to be painted,” also applies to service trucks and the techs who work from them.
“I’ve been around techs who have 20 years of field experience working on heavy equipment, some of the best techs in the industry, who don’t understand or take time to do maintenance on their (service) truck’s compressed air system,” says Terry Vittatoe, director of service and warranty with Vanair Manufacturing Inc., based in Michigan City, Ind. “They’re so busy fixing or maintaining other people’s equipment that they don’t take time to work on their own equipment.”
It’s easy to overlook the compressed air systems on modern service trucks. Most systems run hundreds, maybe thousands of hours with minimal attention. But when problems develop, they’re often related to simple maintenance issues or incorrect operation.
Many field service techs began their careers using compressed air provided by conventional reciprocating-type air compressors. A trend toward rotary screw air compressors on service trucks favors different operational practices to optimize compressor performance and longevity.
Use it or lose it
“Rotary screw compressors are designed for continuous use,” says Jeff Newell, sales manager with American Eagle Accessories Group, which is based in Garner, Iowa. “They need to run for 20 to 30 minutes at a time to let them get to full operating temperature. Condensate (moisture) is a normal by-product of compressing air. If the compressor doesn’t run long enough to warm the oil and vaporize any moisture that’s condensed in its lubricating oil, that moisture keeps building up and eventually contaminates the oil enough to cause problems. Once you turn on a rotary screw compressor, just leave it running. It will go to stand-by when it reaches operating pressure, and turn on and off as needed to maintain that pressure.”
Another operational characteristic of rotary screw air compressors is their need for frequent use. It’s best to operate them regularly, even during storage, to prevent oil drain-back or moisture-induced corrosion between close-tolerance components.
“Our owner’s manuals recommend running rotary screw compressors at least once a month,” says Darren Darnley, a national sales rep with VMAC Compressed Air Systems, based in Nanaimo, B.C. “Sitting idle for a couple months can contribute to premature failure. Just start them up and run them long enough to get them to operating temperature, even when the truck isn’t in regular use.”
All on-board air compressors benefit from simple, regular maintenance. Clean, correct oil is the lifeblood of air compressors. A daily check of oil level in the compressor’s sight glass is a good maintenance procedure — if the location of the sight glass hasn’t been modified. Vittatoe recalls one situation where compressor problems were eventually traced to the way the unit was mounted in its service truck.
“The unit was mounted under the service truck body, and they’d added a two-and-a-half-foot pipe to extend the sight glass out so they could see it without crawling under the truck,” he says. “Unless the truck was sitting perfectly level side to side and front to rear, the extension could make the sight glass look full even though the oil level was actually low, so the compressor was starving for oil even though the operator checked it daily and it looked like it had plenty of oil.”
Beware of making modifications
After-sale modifications to mobile compressed air systems may make the systems more user-friendly but ultimately inhibit performance. Adding extra hose reels, water traps, or oilers — as well as creative plumbing — can overload and overwork compressors.
“We have guidelines on where to mount oil coolers to get adequate air flow, where to mount the air cleaner to keep rain water out — things like that that guys might not think about if they’re rigging their own system,” says Vittatoe. “It’s also important to keep in mind pressure drop and line loss. If a customer orders a compressor to produce 110 pounds per square inch of pressure (psi) at ‘x’ cubic feet per minute (cfm), then installs a couple hose reels so he’s running through 500 feet of hose, he’s probably not going to get the pressure and cfm he wants at the end of the hose. Or, if he plumbs a bunch of elbows and T-fittings into the air delivery system, every fitting causes a little loss of air flow.”
Darnley says customizing or altering air delivery systems on service trucks is a common contributor to diminished compressed air capacity.
“The fitting out of the back of our tanks is three-quarters-inch i.d. (inside diameter),” he says. “If you plumb in a ½-inch i.d. fitting anywhere in the system, or use a 3/8-inch coupler or nipple on your air wrench, the entire system’s capacity immediately is reduced to the smallest i.d. in the system. One 3/8-inch nipple reduces a three-quarters-inch system to 3/8-inch capacity.”
After-sale customizing can also cause problems for hydraulically driven air compressors when additional hydraulically powered systems are plumbed into the air compressor’s power supply.
“They need to be sure the second (hydraulically powered) tool or system is plumbed correctly,” says Newell. “We’ve seen situations where the return hydraulic flow from the additional hydraulic unit was plumbed so it backfed into the air compressor’s drive, and it eventually over-pressured and blew out the oil cooler on the air compressor.”
Ultimately, proper installation, appropriate operation and simple maintenance are the keys to optimum performance from mobile compressed air systems. Simply changing oil and filters at recommended intervals is often enough to provide years of trouble-free service.
“Both reciprocating and rotary screw compressors need to have their oil and air filters changed at recommended intervals,” says Vittatoe. “Rotary screw compressors are a little more touchy about regular oil changes. Make sure you use the recommended oil and filter. Grabbing whatever oil a mechanic has on his truck, or cross-matching an automotive filter from an auto parts store isn’t good enough. We specify a specific type of oil and a specific design of filter for a reason. Going against those recommendations can cause problems.”
“We really don’t see a lot of warranty issues on our compressed air systems,” says Darnley. “We run two percent or less warranty claims. Most of the problems we hear about could be avoided by simply operating the systems correctly and doing basic oil and air filter maintenance at recommended intervals. That’s really all it takes to get hundreds and hundreds of hours of use out of a mobile air compressor.”
Dan Anderson is a part-time freelance writer and full-time heavy equipment mechanic with more than 20 years of experience working out of service trucks. He is based in Bouton, Iowa.