Setting up an air system is no longer an "I’ll take that one" proposition. Today, shop owners with heavy investments in painting and pneumatic equipment have, instead, chosen to be selective and define the exact tolerances they must have for their respective applications before purchasing any system.
More specifically, many shops that have been operating for 20 or more years are upgrading their current air systems to modern, trouble-free, single- and dual-supply pneumatic systems that are fail-safe in design and easy to use.
Whether you’re one of those veteran shop owners with 20 years experience or a new owner opening your first shop, consider the following specifics before you purchase and install your new or upgraded air system.
Single-stage, one-lung, piston-type compressors aren’t commonplace in today’s automotive collision and paint shops, but piston designs with two-stage capability are. If your shop does a lot of hard-core grinding, buffing and other simultaneous, high air-consumption chores, a compressor with a 10 or 12 horsepower rating, a 120-gallon tank and 32 to 38 scfm may be just what you need.
Once you’ve determined the compressor size that’s big enough to handle all your ordinary needs, add 10 percent to the equation — especially when looking for a compressor with high volume and pressure.
When deciding where to set up your shop’s compressor work station, safety should be your first concern. The compressor should be enclosed in its own cubicle or space with enough room around it to allow for free air cooling and heat exchange. Keep in mind that noise generated by the machinery, as well as hot surfaces and moving parts, can cause injury and result in lost production. The space should also be vented through a stationary or active ventilator to outside air, the source of which must not be taken around or near paint spray filter outlets, VOC-recovery areas or areas exposed to propane, butane or gasoline fumes. Clean, dry air drawn into the compressor intake will allow for a better, dryer, air-supply system for use in painting, lifting and handling equipment, pneumatic hand tools and other accessories.
Your compressor should also be located as close as possible to the major artery of air supply without interfering with other work-station operations that might be affected by power surges (the sort of thing that disables your PC) or the noise associated with a large compressor unit. For example, don’t locate the compressor in the same vicinity as the customer drive-up area or entrance, where the service writer or estimator must converse with clients. Also, compressor mounts should be rubber to concrete casements to limit vibration and provide for easy serviceability.
Even the best air compressor won’t prove beneficial to your shop without the right plumbing to carry the air to its intended work sites.
Many shops subscribe to the two-tank system theory. This means that the compressor is located on one side of the shop, and a continuous loop of pipe is run along the wall or overhead through a second tank set up half way through the loop. This is done to prevent large pressure drops during peak demand situations.
Other shops break the system down further by adding a second compressor and a pristine tank (sometimes made of stainless steel) in place of, or parallel, to the second tank. This compressor and clean reservoir are used only for spray guns and paint work. The gate valve, or globe valves, on the outlet side that shut off the system from the main line have a check valve facing away from the paint-only compressor.
Running the Line
An air line that’s run 4 feet high along the wall should slant backward slightly toward the compressor or have low point drains tied into the loop at several locations to serve as condensed moisture traps. Water separators with filters, sometimes called transformers, are placed in series at supply tanks or at the reservoir for the compressor if there’s only one tank. Looping overhead necessitates secondary branch lines to form service lines for couplings, but these must be installed to discourage the entry of water. They’re also slanted toward common drain points or water traps. High-volume shops use both desiccant and centrifugal filtration systems in tandem when air is used for hand tools or painting.
Any time steel plumbing is used, it should be supported frequently with straps or other restraints to ensure solid mounting. Also be sure to maintain drain back toward low-point purge outlets.
Note: Check with local and state officials regarding specific codes relating to the installation of any air or electrical configurations of a new air system. Electrical codes vary from state to state and safety requirements may require an isolated, three-phase electrical circuit for the air compressor. Air lines that are exposed may be required to be supported every 24 inches along a wall or every 36 inches in overhead installations.
Air plumbing should be black steel or galvanized steel pipe of schedule 40 or better wall thickness. Type "K" or "L" copper tubing may be substituted for the steel pipe, but beware of sweated joint problems and contamination with flux for a short time after the installation. Air filters here are more than a must until the system cleans itself out during ordinary use.
Also, the longer the service loop, the bigger the diameter should be for adequate volume. A 10- to 15-horsepower compressor should be coupled to 1 1/4- or 1 1/2-inch pipe if the length of the loop is longer than 100 feet. When auxiliary tanks are in use, the diameter rules still apply.
Some screw-type compressors can provide high-volume air flow and require smaller plumbing, but my experience says bigger is better — stay with the bigger sizes when the loop is longer than 100 feet.
Single- or three-phase power must be available to operate magnetic starters for heavy, high-draw air compressors. Some exceptions include newer oilless compressors with pressure switch controls and without magnetic motor starters. Many screw-type axial compressors run quietly and supply a large volume of air very efficiently. A piston-design compressor will also work well, but it requires more maintenance and creates more heat and noise.
Thermal Conditioning and Purification Equipment
In some areas of the country, the climate and environment require special equipment to handle dampness and dirt-laden air. These special combinations of systems may include an aftercooler, which is used to drop temperature and remove most of the heat and water, as well as oil and lubricating mists. The crossflow design of the aftercooler works wonders by providing a flow of water in the reverse direction as the air circulation inside an efficient convection heat-exchange unit located between the compressor and the air service tanks. Also integral within this loop is an automatic air dump or moisture trap that will release accumulated moisture and hold other residue in a screen filter for periodic service. The last member of this service team is a high-capacity air dryer that not only uses chemical dryers but adds high-capacity refrigeration to prevent supply-line condensation, which will ensure a dry air supply through the system.
Air systems can live and die by ordinary maintenance standards, so remember the following tips.
• Shops with 100 feet of line or more should be draining off or purging systems twice a day in moderate heat and humidity areas.
• Check compressor oil daily in those systems not considered oilless.
• Remember to examine belts, compressor mounts, electrical connections, as well as gauges and valves, whenever oil is changed at manufacturer-approved intervals.
• Keep the fins of cylinders clean, and manually test the pressure unloader and relief valves often to ensure they work properly.
• Filter and strainer replacement should be taken care of at intervals, which are based upon hours operated or when use cycles show a pressure drop across the filter or in the system downstream loop.
• Keep all guards in place and provide warning signs indicating that "machine starts suddenly" to avoid run-ins with state and federal agencies watching out for workplace safety.
• Never break into an air system or attempt to service the system without totally depressurizing it and shutting down the electrical power. Because steel and aluminum housings get hot when air pressure is being boosted to a higher level, be careful not to burn yourself while working around the unit.
A Successful System
Whether you’re a new shop owner looking to purchase your first air system or a veteran owner interested in upgrading your existing system, do your homework before you make your final buying decision. Consider all your shop’s pneumatic demands, as well as any environmental or state regulations that might affect the installation of your new system. Once installation is complete, be sure to follow a proper maintenance schedule to ensure your system operates at maximum efficiency for years to come.
Routing clean, dry air to the right place at the right time is the final goal of any in-shop air-supply system; increased profits are the final goal of any shop owner. By purchasing the right air system for your shop, installing it correctly and maintaining it routinely, you can ensure both goals are met.
Writer Bob Leone, a retired shop owner, is ASE Three-Way Master Certified and is completing qualifications as a post-secondary automotive instructor in the vocational school system in Missouri.
Cleaning sludge and debris from an air system is the job of filter devices. Filtration of particles of 25 microns or less are taken care of with elements of woven screen, woven screen wire over kevlar mesh, sintered bronze, ceramic elements and, of course, controlled path airflow used to separate water droplets and heavy particles.
Certain designs employ moving parts to spin rotator-style blades which use circular motion and rapidly hurl impurities from the surface of the air stream toward the outer walls of the filter housing. Once the walls are contacted, debris then can settle into a holding pocket, which may be purged off at a service interval.
Many filters or active filtration units include chemical moisture separators. Filters such as these can be installed at strategic points in an air loop or be used to offer extra protection when a major purification system is in use.