Pump Core Design

For the first turbopump we are building, one of the major items we wanted to develop was a common, reusable pump core that contains all of the important rotating internals such as bearings and the main shaft. This would allow us to change the turbine and pump designs without having to completely redesign a new core with different internals. Furthermore, this is where the main seals are located to isolate the water and air from the sensitive bearings.

The body of the core is 6061-T6 aluminum with threaded mounting holes for the pump and turbine housings. Numerous bores are to be machined into the stock that will accept the different rotating components and will need to have a high degree of concentricity to prevent shaft binding and premature wear on the bearings. 

Turbopump V1 Shaft Design

 For the shaft design, the carriage came somewhat before the horse with the creation of the rough geometry without any calculations necessarily being done. It was eyeballed off of the relative sizing of both the initial impeller and turbine. Once the shaft geometry was determined, a minimum diameter sizing calculation was done to make sure the shaft would not fail in torsion. Below is that calculation. 

The minimum shaft diameter was determined to be 0.169" in diameter with a 2x factor of safety. The current design has the smallest diameter of the shaft at 0.25", more than enough margin.