With pressure accumulation (or buffering) the conveyor or system that receives and holds the products does this in a way that slowly builds pressure between the buffered products (also known as backpressure). Some products can perfectly handle pressure when buffered or accumulated. Other products can be damaged by the pressure or worse, break. On the other hand, with a zero pressure accumulation (or buffering) the products are accumulated in such a way that it avoids the producsts building up pressure. The products are stored in such a way that they don't touch each other.