Pigging system

Pigging is a method of pushing product residue out of a pipe into a tank or filling machine instead of flushing it down the drain.

When product transfer is complete, some product always remains in the pipeline: on the pipe walls and in the pipe itself. In the traditional approach, it is flushed out with water, so it ends up in the wastewater. A pigging system sends a special flexible plug, called a pig, into the pipe, which fits tightly against the walls. Compressed air, nitrogen, water or the next batch of product is fed in behind the pig. The pressure pushes the pig through the pipe, and the pig pushes the product ahead of it to its destination. The pig then returns to the launch station, often after CIP cleaning, ready for the next cycle.

The name comes from oil pipelines, where pigs were used to remove deposits. In the food, cosmetics and chemical industries, however, the main purpose is to recover finished product. A pigging system can recover up to 99.5% of the product left in the pipe.

Example: A plant produces wet dog food. Meat slurry flows through a pipeline from the mixer to the can filling machine. When a batch is finished, thick slurry that sticks to the pipe walls remains in the pipe. Instead of flushing it down the drain, the plant sends a pig through the pipe, driven by compressed air. The pig pushes the slurry into the filling machine, so it ends up in the cans. The pipeline is then cleaned using the CIP system, and the pig returns to the launch station, ready for the next cycle.