I'm trying to mechanically interlock three small 3/8" valves so that only one of the three is available at any one time. This is three gas supplies to a piece of small equipment, which are subsequently tied together. The interlock is to prevent backflow from one to the other.

Searching eng-tips has shown up Castell and similar interlocks and interlocking via AOVs and the DCS. Given the line size, both of these seem rather over the top. I'm thinking along the lines of discs with cutouts, but can not come up with a layout that I can convince myself will work. Any other suggestions from anyone?

If you already have the valves etc. then this will not interest you - but swagelock makes som block assembly sample valve ports where you can "stack them":These are actuated by air.But max port size is 1/4".It would be more practical and safer to simply put check valves in the lines to prevent back-flow.

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