Diffusers in turbomachinery are used to transfer some of the kinetic energy of the fluid to pressure energy and to direct the fluid to the ducting/second stage/... I understand this and the mechanism behind it (geometry of diffuser changes the mass flux which creates a pressure gradient which decelerates the fluid) but I just cannot find any information how diffusers create more suction at the inlet of the pump/compressor. In laymans terms, how does the diffuser make the pump better for the end user? Is it more efficient?
This website puts it pretty well: http://bellgossett.com/hydronic-plumbing-accessories/pump-accessories/suction-diffuser/
Without a suction diffuser, the pump inlet flow is subject to recirculation zones that produce pressure losses and a non-uniform velocity inlet. These recirculation zones can be the result of pipe bends and fittings. A suction diffuser "straightens" the flow and removes these flow structures. An uneven inlet pressure distribution and velocity profile inflicts uneven stresses onto the pump impeller. In absence of these stresses,the pump can operate more efficiently. Pressure losses are also detrimental to pumps since the inlet suction head is reduced. This can cause cavitation of the pump. Does that all make sense?