Sorting Systems in Satisfactory: Smart Splitters and Filters

Sorting a mixed belt is the one logistics problem that genuinely needs the smart buildings. Doing it well comes down to understanding five filter settings, one of which most players never notice.

The five filter settings

A Smart Splitter output can be set to:

Setting	Behaviour
None	Output is disabled. Nothing goes here
Any	Takes anything, competing normally with other outputs
A specific item	Only that item passes
Any Undefined	Takes anything not named by another output on this splitter
Overflow	Only receives when the other outputs are blocked

Any Undefined is the setting that makes sorting systems maintainable, and it is the one people miss. On a splitter filtering Iron Rod to one output, setting a second output to Any Undefined sends everything else onward without you having to enumerate what “everything else” is.

Compare that to Any, which competes with your named filter for items it could also take. Any Undefined explicitly excludes what the other outputs have claimed.

Overflow is a pressure valve, not a sorter

Overflow only passes items when every other output is backed up. That makes it the correct setting for a relief line into storage or an AWESOME Sink.

The mistake worth avoiding: Overflow is not “the leftovers”. If your named outputs are flowing freely, an Overflow output receives nothing at all, even if the items it would accept are passing by. For leftovers you want Any Undefined; for pressure relief you want Overflow.

Getting these two backwards produces a sorting line that either never fills the sink or diverts everything into it.

Throughput and buffering

Three figures worth knowing:

All splitter types run at 2,000 items/min. That is well above even a Mk.6 belt at 1,200/min, so the splitter is never the bottleneck. Whatever is limiting your line, it is not the splitter.

A splitter buffers nine items. When all outputs are blocked it fills that buffer and then stops accepting from the input, which is what backs the line up.

Splitters only divide across the outputs you actually use. Two connected outputs give you halves; three give thirds. This is the basis of simple early smelting ratios, and it means leaving an output unconnected is a deliberate choice rather than a mistake.

Building a sorting line that does not jam

The standard pattern for sorting a mixed belt into several destinations:

One Smart Splitter per item you are extracting, chained in series along the belt.
Each splitter: one output filtered to its item, feeding that item’s destination.
Second output set to Any Undefined, feeding the next splitter in the chain.
At the end of the chain, everything unclaimed arrives. Send it to storage, or to a sink through an Overflow output.

The failure this avoids: if any destination fills and its splitter has nowhere else to send items, the whole chain stops. Giving every filtered destination an overflow route — or accepting that it stops on purpose — is a decision to make deliberately rather than discover.

Programmable Splitters

The Programmable Splitter works identically but allows multiple item filters per output. That turns a chain of five Smart Splitters into one building.

It costs Computers and High-Speed Connectors, so the trade is materials against space and complexity. For a genuinely mixed belt with many item types — the output of a container farm, or a Lizard Doggo enclosure — it is worth it. For separating two items, a Smart Splitter is cheaper.

Vertical splitters

Since 1.1, splitters can be placed directly on Conveyor Lifts, becoming Vertical Splitters.

This matters more than it sounds for multi-floor factories. Previously, sorting on a vertical run meant breaking out to a horizontal section, splitting, and going back up. Now a lift can sort as it climbs, which keeps a vertical layout genuinely vertical.

Where sorting is actually needed

Worth asking, because sorting is frequently built where it is not required.

Genuinely needed: the output of a storage bank containing mixed items, the return line from a Lizard Doggo farm, a shared belt serving several unrelated production areas.

Usually not needed: a production line making one thing. If a Constructor produces only Iron Rod, a plain splitter distributing to consumers is simpler and cheaper.

The general rule: sort as late as possible. Every item type you can keep on its own belt from the source is one you never have to filter out later, and dedicated belts are easier to diagnose than a sorted mixed line.

A worked example: emptying a mixed storage bank

The most common real sorting job is a bank of containers holding a jumble of items you collected over hours, and you want the useful ones back in circulation.

The arrangement that works:

Belt everything out onto one line. Do not try to sort at the containers — you would need a splitter per container and the filters would have to know what is inside each one.

Chain Smart Splitters along that line, one per item you want to reclaim. Filtered output goes to that item’s storage or straight into production; Any Undefined carries the rest onward.

End the chain at an AWESOME Sink. Whatever nobody claimed becomes coupons. This is the right destination because the alternative — another container — simply recreates the problem you were solving.

Order the chain by volume, not by value. Put the most common item first. Every item removed early is one that does not have to traverse the rest of the chain, and a chain whose first splitter rarely fires is a chain doing unnecessary work.

When the chain backs up

A sorting chain stops for exactly one reason: something downstream cannot accept items and there is no alternative route.

Diagnosing it is mechanical. Walk the chain forward from the input. The first splitter whose outputs are all blocked is the one holding everything up, and the blockage is in whatever that splitter feeds.

The prevention is to give every filtered destination somewhere to overflow, or to deliberately accept that a full destination halts the line. Both are legitimate; what causes trouble is not having decided which.

Common mistakes

Using Any where you want Any Undefined. Any competes with your named filters.

Using Overflow as a leftovers output. It only passes when everything else is blocked.

Sorting a single-item line. A plain splitter does the job.

Assuming the splitter is your bottleneck. They run at 2,000/min, above every belt.

Building the sort at the start of the line. Sort late; keep separate belts separate.