Concentric vs Eccentric Reducers: Key Differences and Applications

What Is a Pipe Reducer?

A reducer connects two pipes of different diameters in a piping system. It smoothly transitions flow from a larger line to a smaller line or vice versa. There are two primary designs: concentric and eccentric. Each serves distinct engineering purposes.

Concentric Reducers: Centered Transition

A concentric reducer is symmetrical around the pipe centerline. Both inlet and outlet pipes share the same central axis. It is typically used in vertical piping runs, where maintaining a centered flow path is required. It is the standard choice for gas, steam, and liquid lines that do not risk pocketing liquid.

Eccentric Reducers: Offset Transition

An eccentric reducer has one side parallel to the pipe, meaning the centerlines of the two ends are offset. This design prevents liquid accumulation at the transition point. It is essential on horizontal pump suction lines, where trapped air or liquid can cause cavitation and poor pump performance.

Common Installation Mistakes

Installing a concentric reducer on a horizontal pump suction line can create a pocket that traps air, leading to cavitation and pump damage. Conversely, using an eccentric reducer where the flat side is facing down in a gas line can cause liquid pooling. Always orient the eccentric reducer with the flat side up for gas service and flat side down for liquid suction service.

Making the Correct Selection

Choose concentric reducers for vertical lines and general purpose transitions. Choose eccentric reducers for horizontal suction applications and any service where liquid or gas must not collect at the transition point.