Vacuum Flow Requirement Tool
Enter mold cavity volume and target vacuum pressure to get required vacuum pump flow (L/min) for a chosen pull-down time.
Calculate NowVacuum Pump Flow Calculator
Methods & Formula
We adopt the standard exponential evacuation model (first-order approximation for uniform volume with negligible flow resistance):
Where:
- P(t) = Pressure in chamber (Pa) at time t
- P₀ = Initial pressure (ambient, Pa)
- S = Pumping speed (L/s)
- V = Chamber volume (L)
- t = Evacuation time (s)
Solving for required pumping speed S:
Then converting to common output units:
With safety/leakage factor applied:
Note: This model assumes ideal gas behavior, approximately constant pumping speed, and negligible flow resistance. For long piping, high flow rates, or very low final pressures, more precise calculations using pump speed curves (S(P)) and system conductance are required.
Example Calculations
Small Mold (Fast Evacuation)
Medium Mold
Deep/Large Mold
Frequently Asked Questions
The safety factor accounts for system leaks and other losses. For most thermoforming applications:
- 20-30% for well-sealed systems with short piping
- 30-50% for systems with longer piping runs or more connections
- 50-100% for systems with known leaks or when designing for future expansion
Common conversions:
- 1 atm = 101325 Pa = 1013.25 mbar = 760 Torr
- 1 mbar = 100 Pa
- 1 Torr ≈ 133.322 Pa
The calculator automatically handles all conversions internally.
For requirements above 1000 L/min (16.67 L/s), consider:
- Using multiple pumps in parallel
- Increasing the allowable pull-down time
- Adding a vacuum reservoir to handle peak demands
- Using a two-stage pumping system (roughing pump + booster)
At higher altitudes, atmospheric pressure decreases, which affects:
- The initial pressure (P₀) - use the actual local atmospheric pressure
- Pump performance - some pumps may have reduced capacity at altitude
- Cooling - air-cooled pumps may require derating
Adjust the "Ambient pressure" field in advanced settings for altitude corrections.
Displacement (theoretical pumping speed) is the volume of gas moved by the pump per unit time, while actual pumping speed is the effective speed at the vacuum chamber. The difference is due to:
- Conductance losses in pipes and fittings
- Pressure-dependent pump performance
- Gas composition and temperature effects
Our calculator accounts for these factors with the safety factor and optional pump correction.
Vacuum seal quality is critical for efficient thermoforming:
- Poor seals can double or triple required pump capacity
- Leaks reduce the achievable vacuum level
- High-quality silicone or rubber gaskets are recommended
- Regular inspection and maintenance of seals is essential
Always include an appropriate safety factor to account for potential seal degradation over time.
Yes, this calculator is suitable for various vacuum applications with some considerations:
- For high vacuum applications (below 1 Pa), gas desorption becomes significant
- For vacuum furnaces, consider outgassing from heated materials
- For vacuum packaging, account for product outgassing
- For semiconductor processes, consider gas load from process gases
Adjust the safety factor accordingly based on your specific application requirements.
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