March 2023

Pathfinder Centrifugal Water Pump

Building and iterating at a small scale helped me better understand centrifugal pump design principles. At the time I was mostly expirimenting out of curiosity but through the process I was able to test Ideas and identify challenges as well as potential solutions in preparation for LOX pump development.

One flaw in the design of this subscale pump was the mechanisms for sealing. A different method of sealing will be developed for Bandit using the lessons learned in this campaign and probably a lot of trial and error.

An important part of the motor sizing process is being able to predict the pump’s mechanical & hydraulic efficiency for a given flow rate and specific speed. This subscale experiment corroborated existing literature and increased my confidence in sizing motors for the Bandit pumps.

Complications with the motor speed control system prevented me from pushing the pump as far as I wanted to but the performance was promising.

Max Speed: ~12500RPM

Max Pressure Rise: ~75psid

Max Discharge: ~130psia

Max Primary Flow Rate: 0.245 Kg/s

Spectrograms of each test’s audio data were generated to provide insight into the shaft speed over the course of the test. The dominant frequencies in the spectrogram correspond to physical features and imperfections of the rotor as it spins. The shaft speed is taken to be the lowest frequency line (once per rotation). The data to the right show nearly 200Hz after the pump reaches full throttle which corresponds to 12000 rotations per minute.

Below is the pressure rise from the 14th test and a screenshot from the video of the 7th test showing the full pressure ladder of a test in-progress.