Vacuum Pump Down Time Calculator
Estimate isothermal pump-down time and a constant-throughput pressure floor from chamber volume and effective pumping speed.
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Result
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Calculation steps
Work through one step at a time or reveal the complete calculation. The steps use your current inputs.
How to calculate
Solve the constant-speed chamber pressure differential equation with a constant gas throughput term.
Pfloor=throughput/S; t=(V/S)ln[(Pinitial−Pfloor)/(Ptarget−Pfloor)]
Worked example
A 100 L chamber with effective pumping 10 L/s and zero gas ingress has time constant 10 s. Pumping 100000 Pa to 100 Pa takes 10 ln(1000)≈69.0776 s in the model.
Assumptions and input details
Pressures are absolute. Chamber volume, temperature and effective pumping speed are constant; throughput is a constant Pa·m³/s quantity. A target at or below throughput/speed is unreachable in finite time. Real pump curves, tube conductance, vapor/outgassing changes, leaks and material effects are excluded. This is an ideal gas-removal calculation, not an equipment recommendation or guaranteed evacuation time.
Unit definitions
Unit selection is independent of language. Each selector contains only units for its physical quantity. Calculations use defined base units internally.
The 36 volume definitions distinguish US liquid, US dry and Imperial measures. Cups carry an explicit definition. Japanese shō is 2401/1331 L and a gō is one tenth of it; the explicitly labelled 180 mL rice cup is separate.
Regional measures are not interchangeable merely because their names look similar. This is a documented selection, not a claim to include every historical unit.
NIST measurement tables · UK Imperial definitions · Japanese traditional units · Mainland China and Hong Kong unit distinctions
Using this calculator
Can I enter my own problem?
Yes. Replace the example values with your own inputs. The result, calculation steps, tables and applicable diagrams update from those inputs. Blank or invalid values clear the result; example values are never silently substituted for missing inputs.
Are the results exact?
Results use floating-point arithmetic and displayed rounding. Read the formula, assumptions and any stated data precision before interpreting the result.
Is my input uploaded?
The calculation runs in your browser. No account, file upload or external AI service is required. Inputs are not saved between page reloads.
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