A useful compressor enquiry starts with the production process. Before choosing a motor size, describe the air that your equipment needs and when it needs it. This guide turns those requirements into a shortlist that suppliers can quote on the same basis.
Start with a one-page demand brief
List each air user, its required inlet pressure, stated flow, operating hours and whether it runs continuously or in short bursts. For an existing factory, log representative production shifts, including changeovers and quiet periods. For a new line, ask the machine builder for consumption at the intended operating settings. Keep assumptions visible so they can be revised after commissioning. CAGI identifies flow, pressure and air quality as the central selection variables.
Specify pressure at the machine
Record the minimum pressure at the most demanding point of use while production is running. Then account for losses through treatment equipment and distribution. An acceptable reading at the receiver does not prove that a distant machine has enough pressure. Ask the supplier to show both the proposed compressor setting and the expected inlet pressure at the critical machine. Resolve unusual high-pressure users separately when practical.
Define air quality before choosing treatment
Ask the process owner to state permitted particles, water and oil at the point of use, with the applicable test basis. A dryer addresses moisture; filtration addresses particular contaminants. Neither a product name nor an oil-free airend alone establishes the quality of air delivered through an entire installation. State the required pressure dew point and the lowest temperature that downstream piping will encounter. Refer to the CAGI drying guide when comparing treatment arrangements.
Match control to the load profile
A relatively steady load and a widely varying load call for different comparisons. Request a fixed-speed proposal and, where useful, a variable-speed proposal against the same operating schedule. For multiple compressors, ask which unit supplies base load, which follows demand, and what happens at the lowest production rate. A VSD label alone cannot establish annual savings; minimum speed, stopping behaviour and coordinated control matter.
Compare complete packages and support
Use declared delivered flow and total package electrical input at stated test conditions. CAGI data-sheet formats help organise this comparison; their existence does not mean that every model or brand is independently verified. Include dryers, drains, ventilation, installation, maintenance and local service in the quotation. Compare alternatives over a common operating period instead of assuming equal running cost from equal motor ratings.
What to send with your enquiry
Prepare: application and shift pattern; measured or documented flow; minimum machine inlet pressure; air-quality requirement; voltage and frequency; ambient temperature and installation altitude; available space and ventilation; expansion plans; and the consequence of an outage. Ask each bidder to identify exclusions and provide a commissioning acceptance plan. Use the sizing guide below to organise the flow calculation before requesting a specific model.
Sources and further reading
Prepared by the LeadCom editorial team from the references below. Selection checklists and examples are editorial guidance; final requirements depend on the process and equipment documentation.