It’s strange—when my 4x4 splitter is facing left, everything works perfectly. But if I flip the design to face right, the belts get jammed and the flow stops. (see the red arrow) Can anyone knowledgeable explain why this happens? Is there a technical reason for this behavior, or a fix to make it work properly when facing right?
I’d really appreciate any insights or suggestions!
splitter bug / problem
- brunzenstein
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splitter bug / problem
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Re: splitter bug / problem
There are no bugs visible here.
- brunzenstein
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Re: splitter bug / problem
Thanks - your really swift

Sorry - it was the wrong screenshot - here the right one and the BP
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Re: splitter bug / problem
There's nothing wrong. That lane with the stone items is blocked by the underground entry by purpose. It's the lane balancing part of that balancer. These items are doomed to eternally remain there by purpose, it's an undesired but unavoidable side effect of the balancing.
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Re: splitter bug / problem
The first one will also jam if items are only on one (wrong) side of the belt. Side loading an underground only lets through the product that hits the "open" half of it.
- brunzenstein
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Re: splitter bug / problem
Sorry for bothering everyone — turns out it was just user error on my part.wobbycarly wrote: Mon Jul 21, 2025 8:47 am The first one will also jam if items are only on one (wrong) side of the belt. Side loading an underground only lets through the product that hits the "open" half of it.
Funny how easy it is to miss the obvious... especially when you're probably the oldest Factorio addict around (like me)!
Re: splitter bug / problem
Understanding and debugging complex belt setups is like the child's game to follow some colored thread through an (image of a) ball of yarn until its end at the other side of the image. It's a labyrinth-like game. I play that (in Factorio) every day.
You just need basic knowledge of belt behavior. The only not completely trivial thing is sideloading at underground entries and exits. An entry and an exit piece blocks one lane and allows sideloading for the other. That's a wanted side effect and enables you to block one lane of a belt but not the other.
One lane is like one worm or one thread in that child's game. The other lane is its brother. They travel together, but sometimes one of them stays behind. You follow the worm and see where it will lead you. Splitters double the worm, and sideloading is like a river mouth where one river flows into another.
That's a much more pleasant view of the world than to imagine the mess of cables behind my computer and investigate to which plug the cable leads from this USB device over here.
You just need basic knowledge of belt behavior. The only not completely trivial thing is sideloading at underground entries and exits. An entry and an exit piece blocks one lane and allows sideloading for the other. That's a wanted side effect and enables you to block one lane of a belt but not the other.
One lane is like one worm or one thread in that child's game. The other lane is its brother. They travel together, but sometimes one of them stays behind. You follow the worm and see where it will lead you. Splitters double the worm, and sideloading is like a river mouth where one river flows into another.
That's a much more pleasant view of the world than to imagine the mess of cables behind my computer and investigate to which plug the cable leads from this USB device over here.