hi in this image : https://imgur.com/a/sIWxAsz
here the process of coal liquefaction, for the heavy oil, the output/input work only as an input, whereas for the steam, both work as input and output,
Their is just the unidirectional output wich work for the heavy oil,
For end, the thumbnail for this mod, havn't the additional input/output that their is in the mod (in game).

Hmm. I'll check it out when I get a chance, thanks.

Both inputs are setup exactly the same. The coal liquefaction recipe has a heavy oil input and a heavy oil output. The input is functioning as input-output but the output is a pure output; in this case since the recipe has three outputs, it assigns two heavy oil outputs to fill up the 4 outputs on the still. So this is expected behaviour based on this recipe. In my setup it requires a valve to make sure the output heavy oils gets used before any new heavy oil is added from an external source: https://imgur.com/a/IiQxgBN