H0W mixed flow turbine pumps work
A mixed flow pump is a centrifugal pump with a mixed flow impeller. The specific speeds lie between 35 and 80 rpmfor low-speed mixed flow pumps, and between 80 and 160 rpm for higher-speed mixed flow pumps. Mixed flow pumps cover the transition range between radial flow pumps and axial flow pumps.
The impellers of mixed flow pumps with a low specific speed are combined with an annular or volute casing; those of mixed flow pumps with a higher specific speed are combined with a diffuser and a tubular casing.
The optimum specific speed range for tubular casing mixed flow pumps with regard to construction costs and efficiency is not clearly defined. However, from approximately 130 rpm upwards, the tangential component of the absolute velocity at the impeller outlet becomes so small in comparison with the flow velocity at the pump suction nozzle that the end cross-sections of the volute or annular casing required to convey the flow would become disproportionately large. In such cases the mixed flow pumps would have to be designed with an excessively large radial casing, which would possibly still be viable if made of concrete but very expensive if made of cast iron or steel.
For this reason, mixed flow pumps with higher specific speeds are usually designed with an axial tubular casing and an "onion type" or axial flow diffuser through which the fluid flows towards the discharge elbow and the pump discharge nozzle.