Air Compressor FAD (Free Air Delivery) Calculator
Calculate your air compressor's actual air delivery capacity by entering the compressor specifications below.
List of the Top 10 Best Air Compressor:
Understanding Free Air Delivery (FAD)
Free Air Delivery (FAD) is the actual quantity of compressed air converted back to the conditions of the free atmosphere (standard temperature and pressure). It represents the true capacity of your air compressor system.
Key Concepts in FAD Measurement
1. What is FAD?
FAD measures the actual air delivery capacity:
- Expressed in CFM (cubic feet per minute)
- Measured at standard conditions (14.5 PSIA, 68°F)
- Always less than displacement volume
2. Why FAD Matters
Importance of accurate FAD measurement:
- Determines true system capacity
- Helps prevent compressor overload
- Essential for proper system sizing
- Key metric for performance evaluation
3. FAD vs Displacement
Key differences between FAD and displacement:
- Displacement is theoretical volume
- FAD accounts for all efficiency losses
- Typical FAD is 60-85% of displacement
- More accurate for system planning
Typical FAD Values by Compressor Type
| Compressor Type | FAD/Displacement Ratio | Typical Volumetric Efficiency | Pressure Range (PSI) |
|---|---|---|---|
| Reciprocating (Single Stage) | 65-75% | 70-85% | 100-150 |
| Reciprocating (Two Stage) | 70-80% | 75-90% | 150-250 |
| Rotary Screw | 85-95% | 85-98% | 100-175 |
| Centrifugal | 90-98% | 90-99% | 100-200 |
Factors Affecting FAD
1. Compressor Design Factors
Clearance Volume
- Affects volumetric efficiency
- Smaller clearance = higher FAD
- Typically 5-15% of displacement
Valve Design
- Low resistance valves improve FAD
- Proper timing critical
- Affects pressure drop
2. Operational Factors
Inlet Conditions
- Higher temperature reduces FAD
- Altitude affects air density
- Humidity impact (typically minor)
Maintenance Status
- Worn rings reduce FAD by 10-30%
- Dirty filters can reduce by 5-15%
- Valve leaks significant impact
FAD Calculation Method
Basic Formula
The FAD is calculated using:
FAD = Displacement × (RPM/Compressor Rated RPM) × (Volumetric Efficiency/100) × (Patm/Pinlet) × (Tinlet/Tatm)
Where:
- Displacement = Theoretical pump capacity (CFM)
- RPM = Actual operating speed
- Volumetric Efficiency = Pump efficiency %
- Patm = Atmospheric pressure (14.7 PSIA)
- Pinlet = Inlet pressure (PSIA)
- Tinlet = Inlet temperature (°R = °F + 459.67)
- Tatm = Standard temperature (528°R)
Improving Your Compressor's FAD
Immediate Improvements
- Clean or replace air intake filters
- Repair any air leaks in system
- Ensure proper cooling
- Check and adjust valve timing
Long-Term Upgrades
- Install larger intake piping
- Add aftercooler if missing
- Upgrade to more efficient valves
- Consider variable speed drive
Frequently Asked Questions
Q: Why is my compressor's FAD lower than rated?
A: Common reasons for lower FAD include:
- Normal wear over time
- Inadequate maintenance
- Higher than standard inlet temperature
- Altitude effects
- Pressure drops in intake system
Q: How often should I measure FAD?
A: Recommended measurement frequency:
- New compressors: Baseline then every 6 months
- Older compressors: Quarterly
- After major maintenance
- When noticing performance issues
Q: Does FAD change with pressure?
A: Yes, FAD is affected by:
- Higher pressure reduces FAD
- Approximately 1% per 2 PSI increase
- Multi-stage compressors less affected
- Always specify pressure when reporting FAD
Q: How does altitude affect FAD?
A: Altitude impacts include:
- Lower air density at higher altitudes
- Approximately 3% reduction per 1000 ft
- May require compressor derating
- Turbocharging can compensate
FAD Measurement Standards
International Standards
- ISO 1217: Displacement compressors - Acceptance tests
- ASME PTC-9: Test code for displacement compressors
- CAGI/PNRCC: Standardized test procedures
- DIN 1945: Acceptance and performance tests
Measurement Methods
- Nozzle method (most accurate)
- Orifice plate measurement
- Piston prover technique
- Bag method (for small compressors)
Interpreting FAD Results
Performance Evaluation
Compare measured FAD to:
- Manufacturer's specifications
- Previous measurements (trend analysis)
- Similar units in your facility
- Industry benchmarks
When to Take Action
Consider maintenance or replacement when:
- FAD drops more than 10% from spec
- Progressive decline in measurements
- Cannot meet system demands
- Energy consumption increases significantly