In K2 there is a recipe in the reverse factory 4 to convert 8 sand to 3 stone (based on the reverse crusher recipe, I imagine). When less than 8 sand is given to the machine, the sand moves into the output slot, preventing it from converting any sand on into stone, and the machine becomes blocked. Since sand to sand wouldn't make any sense, is there a way to prevent it from passing through?

There is a setting called "automatic ingredient push", or something like that. This setting was implemented for players who use this mod to recollect scrap from various random items, so they may only end up with something like, 1 half of an underground belt, which can't be recycled on its own, and would thus remain stuck in the input slot, preventing any further recycling.

With it 'pushed' to the output slot, it can be removed from the machine, and keeps the recyclers from becoming permanently stuck (without manual intervention). There is a short delay for this, which seems is not enough for your inserters to place 8 sand in the machine before it triggers.

I believe I made it so this setting can be disabled, if you aren't using the machines in the way outlined above.

Thanks for the response. I did notice the delay. I’ll try to rig some circuit conditions to insert only when there is at least 8…