Selectatec SM
The essential component of the Selectatec system is a steel ball, free to move within a cage between two nylon valve seats (orange in section). Two springs act on the ball, one from within the large gas union below, and the other from within a sliding chromed peg that sits in the vaporizer connector component. Without a vaporizer fitted the gas union spring is the stronger, pushing the ball into the upper valve seat. This means fresh gas arriving via the smaller gas union, and passing through the channel horizontally to the cage around the ball, has to pass directly to the gas union below, and not upwards to the vaporizer connection. When a vaporizer is fitted the chromed peg is pushed downwards, increasing the pressure on the spring within the peg and thereby pushing the ball down into the lower valve seat. As a result fresh gas arriving as before via the channel to the cage is now diverted upwards and into the vaporizer. 1975.

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