Over the same length, a conical reducer has a larger mean diameter than a straight reducer with the same flange terminations. As illustrated by the equation for conductance (C) below, diameter (D) has a third-order effect on conductance. So, if you want to increase conductance, increasing diameter is the best place to start! Reducing length (L) helps as well, but length only has a first-order effect on conductance.
Eliminating bends in a vacuum system is another way to optimize conductance. When it comes to designing a system for optimal conductance, it helps to remember these three characteristics: Fat, Short, and Straight!