Air Compressor for Automotive Painting, Body Shop, Collision and Repair
To achieve the best results with paint application, it is important to understand the process requirements. This includes the type of paint being used. Water-based paints and solvent-based paints are unique and require different levels of compressed air quality.
- Water-based paint: This paint type requires clean, oil-free, dry air to achieve the best paint results without potential fish-eyes or other imperfections. Issues with the finished product can lead to additional re-work or a complete re-paint. Oil-free compressed air is recommended for water-based applications because it eliminates the risk of oil-vapor in the compressed air or oil coming into contact with the paint. Proper carbon filtration can alleviate oil contamination for shops not operating oil-free compressors, however, there is no substitute for a completely oil-free system.
- Solvent-based paints: This paint type requires clean dry air as well, but oil-free air is not a requirement. Shops should use a coalescing filter (for liquids) and a particulate filter to remove impurities from the compressed air. Contaminants will damage paint surfaces and lead to additional labor.
Compressor Sizing and Installation Considerations
Pressure Needs: Each tool in a shop has a recommended required psi. Using an incorrect psi can result in poor performance or can adversely affect the paint application process. Determine pressure needs based on the requirements of the tools.
Air demand: Determine the correct compressor size based on specific compressed air requirements that include psi and cfm. Consider the operating pressure and sum of the average cfm requirement for each piece of equipment in the shop. For example, if a spray gun requires 8 cfm with a use factor of 50 percent, then that tool would require 4 cfm from the total compressed air delivered. To create an accurate estimate of total air demand, do this for each tool in the shop.
Compressed air storage: A rule of thumb for compressed air storage is to have four to five gallons of air storage per one cfm of compressed air delivered. This can vary depending on the specific application and equipment requirements. See the chart below:
In this example, 124 cfm is required. Based on current calculated usage, this is the minimum required. Compressed air systems should be designed to provide 10 to 20 percent more than the current usage requirement in order to handle spikes in use and to prepare for future growth. Site elevation and the relative humidity can directly impact the air system, such as in the example above. Consult a local compressed air representative with any questions before purchasing a compressor.
Questions to Ask
Is oil free air required or is oil-lubrication acceptable? If small amounts of oil in the process is no hindrance, an oil-lubricated compressor is perfectly fine. If oil in the process will affect the final product, an oil free compressor or robust filtration system will be required.
Is dry air required? Air compressors create condensate. Moisture in delivered air can create problems for some applications. Considering a compressor with an air dryer can reduce or eliminate this condensate. Dryers reduce moisture in delivered air and yield a better paint process.
Most medium to large body shops use some form of filtration, though smaller body shops may not. The larger body shops may use point-of-use membranes or desiccant dryers, as well as a point-of-use carbon filter on the paint booth. Drip legs and in-line filters may also be used to capture condensate. Additionally, FRLs (filter, regulator, lubricators) are used to keep tools well oiled.
This common practice can be costly and require frequent replacement of filtration media in multiple places. It is best to install a refrigerated membrane or desiccant compressed air dryer and use coalescing, particulate, and carbon filtration across the entire system. This will minimize cost and cut-down on short-term filter media change-outs.
Ideally, the compressor should installed on a solid, level surface. Adhere to recommended guidelines for spacing around and above the compressor, and allow for proper air flow and maintenance access. The unit should be kept clear of dusty environments to guard against shorter air filter life, poor compressor performance, an diminished air quality.
Piston Compressor: Look for a heavy-duty piston compressor designed for reliability. Perfect for shorter projects, up to 40 percent duty cycle.
Rotary Screw Compressor: Screw compressors are designed to run at 100 percent duty cycle and provide full rated cfm continuously.
Air Treatment: Coalescing two-stage filtration will remove liquids and particulates. Active carbon filtration will remove oil vapor in delivered air.