A common misconception in purchasing an air compressor is that upfront equipment costs are the largest single expense. Often what can happen is that many purchasing departments will typically evaluate the purchase based on the lowest cost. Many manufacturing plants quickly discover the hidden costs and the long-term impact of going with the lowest-cost option (Figure 1.0) when the first electricity bill arrives. For that reason, collecting the necessary research before making a compressor purchase is critical. To effectively compare air compressor options for your facility, I believe there are four main factors to consider. 

Air requirements and flow demand

When a compressor is too large for a given application, it operates at a reduced load, consuming more energy than necessary. Compressors that are too small for the application are not capable of delivering the proper air supply to fulfill the plant’s needs, affecting production time and requiring the purchase of compressors to meet demand. Considerations should also be given to both normal and maximum air demand since compressed air requirements tend to change to over time. For highest efficiency, normal demand should be approximately 65% to 95% of peak output. 

Oil-free or lubricated?    

Consider what the impact will be to your business if there is trace oil in the air system. Could you be subjecting your company to warranty claims or recalls if products are released with trace oil residue? If you use pneumatic instruments, the impact could be substantial in downtime and maintenance from oil contaminating the air system lines. Once the air system is contaminated with oil, it is almost impossible to remove the trace oil in the lines, and this could cause even larger problems if the plant needs to go to oil-free air in the future. Either way, it is important to understand the short term and long term needs of your plant before electing oil-free or a lubricated air compressor.

Maintenance requirements

To properly maintain most air compressors, several components of the oil system, including air filter, oil, filter, and oil must be replaced on a regular basis. Although these costs are fairly standard and comparable, certain compressors require airend replacement every five to ten years due to the close clearance between the compression elements and subsequent wearing of parts. Replacing an airend can cost up to 50% of the original capital equipment cost and require shipping the entire unit back to the factory for rerating. 

Energy consumption

The compressor type and the number of compression stages have a significant impact on efficiency. The more stages a unit has, the more efficient the compressor will be simply because the compression ratio is lower as the number of stages increases. The smaller increments between stages result in a more efficient operation of the compressor because less energy is required to obtain the same final air pressure. The environment the compressor is in can also contribute to efficiency. It is best to provide a dry environment free from debris and dust in the air.

Consider all factors

Aside from the four main factors, other areas could also impact the success of your compressor air system and should be reviewed. These factors include installation costs, capital costs, water supply, and operator training. Table 1.0 provides a quick checklist for your purchase evaluation.  

Conclusions

Many consider compressed air as the fourth utility due to the costs to maintain and power the equipment. However, this does not have to be the case. Taking the time to evaluate your compressed air system is a critical step that should occur before any equipment purchase.  Overall, an educated decision will result in the best air installation efficiencies for your plant and production processes.