be employed. Full port (or full bore) ball valves cause no problems because the inside diameter of the ball opening is the same as that of the pipe. Etymology Some early cleaning "pigs" were made from straw bales wrapped in barbed wire while others used leather. Both made a squealing noise while traveling through the pipe, sounding to some like a pig squealing, which gave pigs their name. In production environments Product and time saving A major advantage for multi-product pipelines of piggable systems is the potential of product savings. At the end of each product transfer, it is possible to segregate the next products using a pigging sphere. Alternatively it is possible to clear out the entire line contents with the pig, either forwards to the receipt point, or backwards to the source tank. There is no requirement for extensive line flushing. Without the need for line flushing, pigging offers the additional advantage of much more rapid and reliable product changeover. Product sampling at the receipt point is faster with pigs, because the interface between products is very clear; the old method of checking at intervals to determine where the product is on-specification takes considerably longer. Pigging can also be operated totally by a programmable logic controller (PLC). Environmental benefits Pigging has a significant role to play in reducing the environmental impact of batch operations. Traditionally, the only way that an operator of a batch process could ensure a product was completely cleared from a line was to flush the line with a cleaning agent such as water or a solvent, or even with the next product. The cleaning agent then had to be subjected to effluent treatment or solvent recovery. If a product was used to clear the line, it was necessary to downgrade or dump the contaminated portion of the product. All of these problems can now be eliminated due to the very precise interface produced by modern pigging systems. Safety considerations Pigging systems are designed so that the pig is loaded into the launcher, which is pressured to launch the pig into the pipeline through a kicker line. In some cases, the pig is removed from the pipeline via the receiver at the end of each run. All systems must allow for the receipt of pigs at the launcher, as blockages in the pipeline may require the pigs to be pushed back to the launcher. Many