Underflow Gate

The Underflow Gate is a Serpulo-exclusive transport block that instantly transmits items through adjacent belts and conveyors, functioning as one of the game's four "instant transfer" devices. It was added in Version 5.0 (build 103) and behaves as the inverse of the Overflow Gate: when deciding how to route items, the Underflow Gate gives priority to outputting items to its lateral (side) directions rather than to the forward direction. This makes it useful for forcing items out sideways while still allowing pass-through or conditional routing in the forward lane.

Underflow Gates are grouped with Sorter, Inverted Sorter, and Overflow Gate as the set of instant-transfer components. These devices do not move items gradually like normal conveyors; they teleport items between connected lanes according to their internal routing priorities and rules. Because they operate on discrete transfer rules, they are commonly used to implement compact routing logic, conditional lane-balancing, and tight item switches that would be difficult or slow with ordinary conveyors.

Practical notes and constraints:

• Placement and chaining: Instant-transfer devices share a consecutive placement limit. You cannot build arbitrarily long chains of these devices; a maximum of 2 consecutive instant-transfer blocks is enforced as of Version 6.0. This prevents abuse of long, pure "light-transfer" lines. The four instant-transfer types count toward the same consecutive limit, so mixing types does not bypass the restriction.
• Historical change: The Underflow Gate was added in Version 5.0. In Version 6.0 the previous unknown item limit was removed and the consecutive-limit behavior was clarified and capped at two.
• Usage patterns: Use Underflow Gates where you want an item stream to preferentially exit to side outputs while still allowing items to continue forward when side outputs are blocked or full. Combining Underflow Gates with Sorters and Overflow Gates allows construction of compact splitter/merger circuits and priority-based distribution nodes.
• Compatibility: As a transport block it integrates with conveyors, routers, and the other instant-transfer blocks; however, designs that rely on long sequences of instant-transfer blocks must respect the consecutive-placement cap.
• Map/sector relevance: The block is flagged as Serpulo-exclusive content, so it appears in Serpulo maps and scenarios where that content set is enabled.

Because Underflow Gates operate by prioritized, instantaneous transfers rather than by moving objects along a physical belt, their behavior is deterministic and best used in compact, logic-like layouts where precise routing is required.