Vacuum Pipe Conductance & Effective Speed Calculator
Model vacuum line conductance across viscous and molecular flow regimes, determine net effective pumping speed at the chamber, and prevent line throttling.
Pump & Operating Pressure
Piping Geometry & Flange Size
Effective Pumping Speed Summary
Piping Geometry & Ratio
Piping Manifold Guidance
Recommended Tools & Equipment
Tested hardware and components for high reliability
Frequently Asked Questions
Why does pipe diameter matter so drastically in vacuum systems?
In viscous flow, conductance scales with the internal diameter to the fourth power (d⁴). In molecular flow, it scales with diameter cubed (d³). Doubling the pipe diameter increases viscous conductance by 16 times (2⁴ = 16), eliminating pumping speed throttling.
What is the "resistors in series" rule for vacuum pumping speed?
The relationship between pump speed (S), piping conductance (C), and effective speed at the chamber (S_eff) follows the harmonic equation 1/S_eff = 1/S + 1/C. If line conductance equals pump speed (C = S), exactly 50% of the pump's performance is lost in the pipe.
What is the difference between viscous and molecular flow?
In viscous flow (pressures above ~1 Torr), gas molecules collide primarily with one another, behaving like a continuous fluid. In molecular flow (high vacuum below 0.001 Torr), the mean free path is so long that molecules collide almost exclusively with the pipe walls, making flow purely geometrical.
How should vacuum line elbows and valves be designed?
Keep vacuum forelines as short and straight as possible. Every 90-degree elbow adds the equivalent resistance of 15 to 20 pipe diameters of straight tubing. Never place a long, narrow hose between a roughing pump and chamber.