When the suction pipe and pump suction flange are not the same size, what should be used to connect them to avoid air pockets?

Using an eccentric reducer or increaser to connect the suction pipe and pump suction flange of different sizes is the correct approach to avoid air pockets. An eccentric reducer features a flat side that allows for a smooth transition in height between the two pipe sizes while facilitating the flow of liquid. This design minimizes the potential for air to collect at the top of the pipeline, which can lead to cavitation and reduce the performance of the pump.

In situations where you need to connect pipes of different diameters, maintaining a consistent flow direction and minimizing disturbances in the flow is crucial. The eccentric shape allows for a more gradual change in cross-sectional area, which helps maintain higher velocities and reduces the likelihood of air entrapment.

While concentric reducers or increasers may connect pipes of different diameters, they create a circular shape that can allow air pockets to form at the top of the pipe, especially when the system is not full or if there are fluctuations in flow. Rigid pipes and domestic pipes, on the other hand, do not address the size differential specifically and may not provide the necessary features to manage air pockets effectively in the system.