Grinder pumps and chopper pumps both macerate solids before the water flows through the pump, but they accomplish the task differently. Grinder pumps grind up the solids into slurry in order to pump the liquid. Chopper pumps combine a solids handling throughlet with fixed cutting blades that chop up the solids that cannot pass through. Grinder pumps are typically used in low flow scenarios with high total dynamic head, TDH, where the peak flow rate is below 75 gpm. Chopper pumps can typically be used within the same range of flow and TDH as a solids-handling pump, i.e. 100 – 5000 gpm. Please see the following video demonstration from Vaughan of a chopper pump. http://www.youtube.com/watch?v=zhTEjFd-vxo Please see the following video demonstration from Goulds Water Technology of a grinder pump. http://www.youtube.com/watch?v=TrbcBcGww2U