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In the current topology, adjustment of the breath rate is achieved by turning the control knob which changes the rate of vacuum bleed. Reducing the supply vacuum too much in this way increases sensitivity to pilot tube positioning and thereby reduces reliability.

The knob used to adjust the vacuum (and effectively control the breathing rate), can fail. The shaft is easily broken when 3D printed especially at low density.

A solid rod could be used to communicate position to the control valve instead of a chord.

As is, the chamber needs only to be less than half the height.

The system control valve toggle mechanism connects and disconnects the pilot tube from the cylinder control port, however the mating of the pilot tube to the receiving port is offset with respect to the radius of trajectory. As a result, reliable operation is overly sensitive to the assembled position of the pilot tube.