Compressor Recovery Time Calculator — How Fast Tank Refills
How fast does a Viair 400C refill a 3-gallon tank? Enter compressor CFM, duty cycle, tank volume, and pressure range — get fill time to ready state.
Compressor
Gallons, including any add-on tanks
Tank PSI right after the blast
Where the pressure switch shuts off
Tank fills in
38 sec
From 120 to 150 PSI on the Viair 400C. Effective output at this pressure: 0.85 CFM.
Compressor shootout — same tank, same window
Shorter bar = faster recovery. Click any row to swap in that compressor.
The math
- Pump-up formula
- t = V×ΔP / (7.48×14.7×CFM_eff)
- Average pressure during fill
- 135 PSI
- Free-air CFM (rated)
- 2.62 CFM
- Effective CFM at this pressure
- 0.85 CFM
Compressor output falls as back-pressure rises. We apply a linear derating (CFM_eff = CFM_free × (1 − 0.75 × P_avg/P_max), floored at 15% of rated) that matches Viair's published fill times. Real-world times also depend on hose diameter, check-valve losses, ambient temperature, and battery voltage — assume ±15% on the answer.
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