An eccentric reducer is a fitting used in piping systems between two pipes of different diameters. They are used where the diameter of the pipe on the upstream side of the fitting (i.e. where flow is coming from) is larger than the downstream side. Unlike a concentric reducer, which resembles a cone, eccentric reducers have an edge that is parallel to the connecting pipe. This results in the two pipes having offset centre lines, unlike concentric reducers. The same fitting can be used in reverse; as an eccentric increaser/expander.

Horizontal liquid reducers are always eccentric, top flat, which prevents the build up of air bubbles in the system. Eccentric reducers are used at the suction side of pumps to ensure air does not accumulate in the pipe. The gradual accumulation of air in a concentric reducer would result in a large bubble that could eventually cause the pump to stall or cause cavitation

Cavitation

Cavitation is the formation and then immediate implosion of cavities in a liquidi.e. small liquid-free zones that are the consequence of forces acting upon the liquid...

 when drawn into the pump.

Horizontal gas reducers are always eccentric, bottom flat, which allows condensed water or oil to drain at low points.

Reducers in vertical lines are generally concentric unless the layout dictates otherwise.

See also Reducer

Reducer

A reducer is the component in a pipeline that reduces the pipe size from a larger to a smaller bore .The length of the reduction is usually equal to the average of the larger and smaller pipe diameters...

.