Factorio Forums

TL;DR

The new fluid mixing prevention for passthrough ports in 2.1 no longer allows using "smoothie pipes" with Electromagnetic plants and Thrusters the way they used to work, even though the "smoothie pipe" mechanic itself remains unchanged.

What?

The "smoothie pipe" mechanic in Factorio is the ability to connect the inputs or outputs of multiple machines with different fluids in a single pipe. The game allows this as long as the connections are unidirectional.

However, the rules change with bidirectional connections. This is explicitly stated in FFF #442 "Fluid mixing prevention":

"Notably, fluid mixing only occurs on bidirectional connections; you can still create smoothie pipes by connecting pumps or unidirectional machine outputs with different fluids in them, and the game will not get in your way."

This system is designed to protect certain machines — such as boilers or steam engines — which have bidirectional connections and only use one fluid. They simply don't need "smoothie pipes."

The problem arises with machines that have bidirectional connections but also use multiple fluids. The new fluid mixing prevention prevents "smoothie pipes" from working with them.

So far, I have only found two machines that fit this description: Thrusters and the Electromagnetic plant (if I'm not mistaken). For these machines, the new prevention system limits the use of "smoothie pipes," closing off interesting design possibilities that existed before version 2.1. I would like the "smoothie pipe" mechanic to remain usable with machines that have bidirectional connections and use multiple fluids.
The GIF below shows the thrusters working when controlled by logic circuits while using smoothie pipes (ver. 2.0.77).

Why?

Technically, smoothie pipes are allowed — just not for this particular case. So why not make an exception for them, somehow? It's an alternative to straightforward pipe routing, and it opens up creative designs that would otherwise require messy pipe spaghetti.