For specific speed 8640 (if this is specific speed for one stage)you have to go with mix flow impeller. Mix flow impeller will give in the end smaller pump diameter whic can reduce cost of bore.
I am looking for a some sofisticated Vibration meter (to measure Displacement, Velocity, Acceleration)with calbles or infra red-wireless. Application is Centrifugal pump industry-HVAC.
Thanks,
Aleksandar Kamenov-Pump Eng
SA Armstrong Ltd
Toronto