Both conveyor node types move material between process steps using length and speed to determine travel time. While everything is running they behave identically. The difference appears only when flow is restricted downstream — and it is the most consequential modeling choice that looks like a detail.
The difference in one sentence
A standard conveyor moves material. An accumulating conveyor moves material and holds it.
When the next machine stops:
- On a standard conveyor, material cannot continue onto the belt. The stoppage propagates directly upstream and the feeding machine is blocked.
- On an accumulating conveyor, material queues on the belt itself. The upstream machine keeps running until the conveyor's capacity is used up.
Why the wrong choice distorts the model
The error runs in both directions, and both are costly:
- A real accumulation lane modeled as a standard conveyor makes the line look more fragile than it is. Every downstream hiccup propagates instantly upstream, so the model reports stoppages the floor does not have — and you end up justifying storage that is physically already there.
- A plain transport belt modeled as accumulating hands the line storage it does not own. The model over-predicts throughput, absorbs stoppages that in reality propagate, and quietly makes the case for doing nothing.
The test is physical, not conceptual. Stand at the conveyor and ask: when the next machine stops, does product keep coming onto this and stack up, or does it stop dead? Roller beds, pallet conveyors and dedicated accumulation lanes accumulate. A simple transfer belt normally does not. Model what the equipment does.
What sets the capacity
Both node types share the same three parameters, and it is the third that does the work.
| Parameter | Controls | Why it matters |
|---|---|---|
| Length | distance travelled | with speed, sets transit time |
| Maximum speed | how fast material traverses | an upper limit on transport capacity |
| Height | units held per unit length | on an accumulating conveyor this is the storage — length × height is how much it holds |
Which leads to the practical point: an accumulating conveyor is a buffer with a travel time attached. Before sizing new storage, work out length × height on the transport you already have — some of the capacity being costed may already be on the floor.
The travel time is not free, though. Unlike a buffer, material on a conveyor must still traverse the length before it becomes available downstream, so a long accumulating conveyor adds latency along with its storage. On a line where material ages or must be tracked, that delay is a real modeling consideration rather than a rounding error.
Choosing, in practice
- Standard conveyor — where travel time or physical layout matters but product does not queue; a straight transfer between two adjacent steps.
- Accumulating conveyor — wherever transport also provides storage, and work-in-process builds along the line rather than in a discrete location.
- Buffer — where the storage is a place rather than a path, and travel time is not meaningful.
Start simple. Get the structure right with rough parameters and refine afterwards — a wrong node type is a structural error that no amount of parameter tuning corrects.
For the throughput argument behind buffer sizing generally, see How big should a buffer be? on the ReliaSim site.