Custom Coaxial Pneumatic Valve

Design Goals and Inspiration

The purpose of a run valve in a hybrid rocket is to hold the oxidizer in the tank before launch, and open on command to flow large amounts of oxidizer into the combustion chamber, as quickly as efficient as possible. As with all rocket components, reducing volume and mass are also paramount. The operating principle of this valve was inspired by last year's design, which had a similar function but designed for nitrous oxide instead of liquid oxygen.

Creating a cryogenic system compatible with liquid oxygen proves to be a significant challenge, especially when it came to effective sealing and material constraints. Specifically, there are three reciprocating spring-assisted PTFE rod seals in the valve, which are best practice for sealing at cryogenic temperatures. Accommodating for these unique seals was a significant challenge. Although there were some minor tweaks and changes after the critical design review, the presentation below encapsulates much of the design inspiration and process.

Manufacturing

The run valve consists of seven parts, all machined in house in the Columbia Makerspace. Six of the parts are stainless steel 303, and one is PTFE, or Teflon. Four of the seven components are designed such that they can just barely be machined in one work holding setup on the  4-axis lathe in the Columbia Makerspace (Haas ST-20Y). The three outer body pieces are far more complex and require extensive milling on both sides after turning on the lathe.  Careful calibration, measurements, and constant attention to geometric tolerances was necessary in order for the valve to be functional.