Two of the simplest machines
Most of a chemical plant is just moving material around and combining it in the right amounts. Two tiny pieces of equipment do most of that work.
A Mixer takes two or more streams coming in and blends them into one stream going out. A Splitter does the opposite — it takes one stream and divides it into parts (say, 70% one way and 30% another). Together they let you route material wherever it needs to go.
Mixers join streams; splitters divide one stream into parts.