The air compressor is critical to conventional air abrasive blasting operations because it must supply the right amount of air at the right pressure to propel the abrasive against the surface. Air pressure is measured in pounds per square inch (psi). Standard atmospheric pressure, which is the normal pressure of air from the weight of the Earth's atmosphere, is 14.7 psi. A compressor creates high air pressure by forcing or compressing large quantities of air into a small space. The air pressure needed to blast steel effectively is 90 to 100 psi at the blast nozzle. In order to obtain this air pressure, a compressor must pressurize its receiver tank to approximately 125 psi.
Another important factor is how much pressurized air a compressor can deliver. This volume or output is measured in CFM (cubic feet per minute), and is determined by the size of the compressor. The more air the compressor can force into the air lines of the blast equipment, the higher the resulting air pressure. The air volume required depends on the size of the blast nozzle(s) and how many of them are used at the same time. If other equipment is being run off a compressor simultaneously, take this into consideration when adjusting the CFM.
There are both stationary compressors, which are found in fixed blasting sites, and portable compressors (Figure 2), which can be moved to jobs as needed. Compressors are either powered by an electric motor or an internal combustion engine that runs on gasoline or diesel fuel.
All compressors must have a label that indicates that certain high-pressure components (receivers, etc.) are built to the National Board of Pressure Inspectors Standards and are registered to meet the American Society of Mechanical Engineers (ASME) code. The compressor must also be equipped with ASME-approved pressure safety relief valve(s) that will vent air pressure if the maximum pressure rating of the equipment is exceeded. If the compressor package does not carry the ASME label and the safety relief valve(s), do not use it. The label certifies to the user that the compressor package can be used anywhere in the U.S. without fear that a State Pressure Vessel Inspector will shut down the job because of non-coded, high-pressure components or inadequate safety devices.
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