Vacuum Chamber Pump-Down Time Calculator

Calculate evacuation time from atmosphere to rough vacuum, high vacuum transition, surface outgassing gas load, and ultimate equilibrium pressure.

Chamber Dimensions & Roughing

Chamber Volume V (Liters):

Internal Surface Area A (m²):

Roughing Pump Speed S_rough (m³/h): Dry scroll or rotary vane

Target Crossover Pressure (mbar): Roughing to high-vac crossover

High Vacuum & Outgassing

HV Pump Speed S_hv (L/s):

Outgassing Rate q₁ (mbar·L/s·cm²): Clean SS: ~3e-9; Baked UHV: ~1e-11

Pump-Down Times & Pressure

Roughing Time to Crossover:

—

Roughing Pump Speed (L/s):

—

Total Chamber Outgassing (Q_out):

—

Ultimate Base Pressure (P_ult):

—

HV Volumetric Transit Constant (τ = V/S):

—

Recommended Tools & Equipment

Tested hardware and components for high reliability

100% Free Tool Zero Sign-Up

Frequently Asked Questions

Why does chamber pump-down slow down dramatically below 10⁻³ mbar?

Above 1 mbar, evacuation is dominated by bulk gas displacement in the volume (viscous laminar flow). Below 10⁻³ mbar, desorption of adsorbed water vapor and hydrocarbons from chamber walls (outgassing) dominates the gas load.

How does high-temperature baking affect outgassing?

Baking stainless steel under vacuum at 150°C–250°C accelerates water desorption by orders of magnitude, reducing post-cooldown outgassing rates from ~10⁻⁹ down to ~10⁻¹² mbar·L/s·cm².

What is the optimal crossover pressure?

Crossover occurs when roughing speed matches turbomolecular pump throughput capacity, typically between 0.01 and 0.1 mbar, preventing oil backstreaming while protecting turbo rotor blades from overheating.