Concentric reducers taper evenly, keeping both pipes on the same centerline. Eccentric reducers keep one side straight: at a pump suction they go in flat on top so no air or vapor pocket forms, and on pipe racks they often go flat on bottom so the pipe keeps its support elevation. Control valves are commonly installed between a pair of reducers because they are smaller than the line.
Eccentric reducer at the pump suction goes flat on top, if you flip it you'll trap an air pocket and air-bind the pump.
On a rack, flat on bottom means the pipe still sits on the same shoe height; that's why the drawing says FOB.
Also heard as
- increaser
Related terms
Swage
A forged reducing nipple that steps a small bore line down one or more sizes, with threaded, plain or beveled ends.
Tee
A T-shaped fitting that splits or joins flow, with a straight run and a side branch.
Elbow
A fitting that changes the direction of a pipe run, usually by 90 or 45 degrees.
Control valve
A power-operated valve that modulates flow on a controller signal to hold pressure, level, flow or temperature at setpoint.