System
Pressure, flow, vacuum, and power units used across compressed air and vacuum — with conversions and instrument notes.
Operating principle
Compressed-air work uses gauge vs absolute pressure, standard vs actual flow, and a mix of imperial/metric units. Knowing the reference conditions (SCFM vs ACFM, PSIG vs PSIA) is essential for sizing and troubleshooting.
Efficiency notes
Standardized reference conditions (CAGI/ISO 1217) let you compare compressor capacity honestly. Always confirm whether a spec is SCFM or ACFM.
Selection guidance
Use gauge for system/mechanical work and absolute for thermodynamic calculations. Match the instrument type to the range and accuracy needed.
Components
- Pressure (PSIG/PSIA/bar/kPa/inHg)
- Flow (SCFM/ACFM/m³/h/LPM)
- Vacuum (mbar/inHg/Pa/Torr/micron)
- Power (HP/kW)
- Temperature (°F/°C)
Common issues
- Confusing gauge vs absolute → wrong sizing
- SCFM vs ACFM ignored → altitude/temp errors
- Using inHg vacuum as a pressure → sign/unit errors
- Metric/imperial mix-ups in specs
Maintenance
- Calibrate gauges/transmitters per schedule
- Reference conditions: SCFM at 14.5 psia, 68°F, 0% RH (CAGI)
- Log instrument drift
- Use absolute units for thermodynamic calcs
Field tips
- PSIA = PSIG + 14.7 (atm); bar = PSIG × 0.0689
- ACFM = SCFM × (14.5 / actual psia) × (actual °R / 528 °R)
- 1 HP ≈ 0.746 kW; 1 kW ≈ 1.34 HP
- Vacuum: 1 inHg ≈ 33.86 mbar; deep vacuum uses microns/Torr