A reducer is a kind of pipe fitting used in process piping that reduces the pipe size from a larger bore to

a smaller bore (inner diameter).

A reducer allows for a change in pipe size to meet hydraulic flow requirements of the system, or to adapt to existing piping of a different size. The length of the reduction is usually equal to the average of the larger and smaller pipe diameters.

There are two main types of reducer:

• Concentric reducers
• Eccentric reducers

Reducers are usually concentric but eccentric reducers are used when required to maintain the same top-or bottom-of-pipe level.

Concentric Reducer

In Concentric Reducer the reduction of the pipe size is achieved by decreasing the diameter of the fitting 

at a constant rate over a specified length, maintaining symmetry around the fitting. Concentric Reducers

are used to join pipe or tube sections of different diameters on the same axis. They provide an in-line conical transition between pressurized pipes of differing diameters. Thus, concentric reducers connect 

pipes of unequal size but have a common centerline. The same fitting can be used in reverse as an concentric expander.

Eccentric Reducer

In Eccentric Reducer the reduction of the pipe size is achieved by decreasing the diameter of the fitting 

at a constant rate over a specified length, maintaining one side of the fitting horizontally. An eccentric pipe reducer fitting is manufactured with the smaller outlet off center to the larger end, which allows it 

to align with only one side of the inlet. The same fitting can be used in reverse as an eccentric expander.

Uses of Concentric and Eccentric Reducers

In horizontal liquid piping, eccentric reducer must be installed with flat side up so that it can prevent trapping air in the piping system. As an exception, same is flat side down in piperack where same Bottom of Pipe (BOP) has to be maintained. Other exception is with control valves. A eccentric reducer with flat side down will give a more constant flow through the control valve rather than a concentric reducer or eccentric reducer with flat side up, which will give your more flow disruption and will cause problems with your control valve.

In horizontal gas / vapor / steam piping, eccentric reducer must be installed with flat side down which 

allows condensed water or fluid to drain at low points.