Complete Screw Air Compressor Selection Guide: How to Match Pressure, Flow and Power According to Air Demand

1. Core Selection Standards

This guide follows JB/T 6430-92 Oil-Injected Screw Air Compressors for General Use and ISO 1217 Displacement Compressors — Acceptance Test. Many buyers only focus on motor power when selecting compressors, which is a common mistake. The actual usable air output is affected by working pressure, ambient temperature, altitude and pipeline loss. The three core parameters to confirm first are working pressure, required free air delivery (FAD) and matching motor power.

2. Confirm Working Pressure

The working pressure of the compressor must be higher than the pressure required by the terminal equipment. Reserve pressure margin for pressure drop caused by filters, dryers and pipelines. For example, if the workshop equipment needs 7 bar stable air supply, the compressor rated pressure is usually selected as 8 bar. Excessively high pressure will greatly increase power consumption; every 1 bar pressure rise will bring about 6%-8% extra energy consumption.

3. Calculate Actual Air Flow (FAD)

The nominal flow marked on the nameplate is the free air delivery under standard reference condition (20℃, 1 bar absolute pressure). When the site is in high altitude or high temperature environment, the effective air output will decrease. Sum up the air consumption of all pneumatic equipment, add the simultaneous use coefficient and pipeline leakage allowance (generally 10%-15%), and get the required FAD. Do not select the unit only according to the theoretical air consumption without margin.

4. Match Motor Power

After confirming the required flow and pressure, select the supporting motor power. Permanent magnet VSD models and fixed-speed models with the same power have different actual output performance. VSD units are recommended for sites with frequent air demand fluctuation; fixed-speed models are suitable for stable continuous air consumption. Check the rated current of the motor and the capacity of the on-site power distribution cabinet to avoid overload and tripping.

5. Additional Selection Factors

Also confirm ambient temperature, ventilation condition, dust concentration, noise requirement and whether oil-free air is needed. Food, pharmaceutical and electronic precision industries have higher requirements on air quality, and complete post-treatment equipment shall be configured synchronously.