Declared effective-speed interval
Vacuum evacuation time
Inputs
Closed vessel and connected volume represented by this one stated volume.
User-entered effective speed at the vessel for this interval; no pump curve or conductance calculation is applied.
User-entered start pressure in the same absolute-pressure basis as the target pressure.
User-entered target pressure below the start pressure in the same absolute-pressure basis.
User-entered target interval used only for reverse effective-speed arithmetic.
Results
Declared pressure ratio p₁/p₂
10
—Ideal constant-speed evacuation time
23.026
Effective speed for declared time target
11.513
Declared / required effective-speed ratio
0.86859
—t = (V/S) ln(p₁/p₂); Srequired = (V/ttarget) ln(p₁/p₂)
A first-pass number, not a code check, certification, or approval. Read the method and its limits below. What this is and is not.
Nearby: Hydrostatic pressure · Flow continuity · Pipe mean velocity · Bernoulli equation
Method
Formula, when it applies, and when it does not
Calculate an ideal constant-effective-speed evacuation time and reverse required effective speed for one vessel volume and pressure interval.
t = (V/S) ln(p₁/p₂); Srequired = (V/ttarget) ln(p₁/p₂)
When
- Closed declared vessel volume
- User-entered constant effective pumping speed
- Single pressure interval
- Ideal logarithmic pump-down arithmetic
Don’t
- This is a single constant-effective-speed, ideal logarithmic evacuation interval using user-declared vessel volume and effective pumping speed. It does not calculate pump curves, conductance, piping/network losses, leakage, desorption/outgassing, vapour load, thermal behavior, gas composition, compressible/choked flow, equipment sizing, pump selection, capacity, life, safety, or approval. Real evacuation time can be longer than this ideal arithmetic result.