A surge bin is a relatively small-capacity storage vessel positioned between two processing stages in a feed mill, intended to absorb short-term variations in flow rate between an upstream and downstream process so that each can operate at its own optimal, steady rate without being forced to exactly match the other's instantaneous output. Surge bins are not generally intended for extended bulk storage in the way a main storage silo is, but rather to smooth out the inevitable minor timing mismatches that occur between connected but independently controlled pieces of equipment.

A common example is a surge bin positioned between a grinding operation and the downstream batching or mixing stage: the hammer mill may run continuously at a steady rate, while the batching system draws material in discrete batch quantities at intervals — the surge bin absorbs this difference, preventing the grinder from needing to start and stop in lockstep with each individual batch cycle.

Surge bin sizing is a deliberate engineering decision based on the expected flow rate mismatch between the connected processes and the desired operational buffer time, with undersized surge capacity providing little practical benefit (since the bin fills or empties too quickly to meaningfully decouple the two processes) and oversized capacity adding unnecessary cost and floor space without proportional operational benefit.

Level sensing within a surge bin — typically using point-level sensors (high and low level switches) or continuous level measurement — is commonly integrated into the plant control system, allowing the upstream process to be automatically slowed, stopped or started based on surge bin fill level, maintaining the buffering function without requiring constant manual operator attention.

Because surge bins are typically smaller and turn over their contents more frequently than main storage silos, they are also more susceptible to flow problems such as bridging if not adequately designed with appropriate hopper angles for the specific material being handled, making the general principles of feed flowability and hopper design particularly relevant to reliable surge bin operation.

Surge bins are also commonly used immediately ahead of pellet mills to buffer conditioned mash flow, and at various points in finished product handling to decouple cooling, screening, bagging or loadout operations from each other, making the surge bin concept a recurring design element appearing at multiple points throughout a well-designed feed mill rather than a single specific location.