The coupling used to connect two pipes of different diameter is called a reducing coupling. The reducing coupling makes hard economic sense on ler systems or any other piping systems, which require directing, on-the-run. It changes the pipe size, and a coupling joins two lengths of piping of the same size. A coupling connects two pipes to each other. If the material and size of the pipe are not the same, may be called a reducing coupling or reducer, or an adapter.

Reducing flanges are also called as adapter flanges. It is used to connect two sizes; the appropriate reducing flange is inserted between the two and bolted into place. Conductance and pumping speed remain virtually unchanged. It is designed for use in changing diameters in a piping system. A reducing flange consists of a flange with one specified diameter having a bore of a different and smaller, diameter. Except for the bore and hub dimensions, the flange will have dimensions of the larger pipe size.

Reducing regulator is a simple control device in which all the energy to operate it is derive from the control system. It is designed for industrial furnaces and heating application. It can be used to control flow, lever or pressure. It maintains a desired reduced outlet pressure while providing the required fluid flow to satisfy a variable downstream demand. The value at with the reduced pressure is maintained is the outlet pressure setting of the regulator. These regulators can maintain a constant outlet pressure over a wide range of flow even if the inlet pressure varies.