A bellmouth (also called a suction trumpet, used in conjunction with a centrifugal pump) is a nozzle-shaped inlet casing assembly (see accessories), usually used for vertical tubular casing pumps.
The horn-shaped flow acceleration minimizes the irregularity of the velocity distribution. The uniform velocity distribution ensures uniform approach flow (see inlet conditions); this is especially important for high specific speed pumps (see specific speed).
If there is eddy current at the inlet, a rectifier should be installed to provide a certain degree of rectification.
Bellmouth: high specific speed pump with Bellmouth and flow correction
If pre-swirl flow control is provided downstream, there is no need to install a rectifier in the bell mouth.