Instead of blood, the pump pushes water through the lines in order to keep the system up and running. OCH uses a 145GPH pump which is more then enough for our setup! They also give you the ability to install two pumps in the water container! Why? Duallies! Indeed ... That way you have to seperate water flows ... one for each cpu. With one pump the cold water goes into the first cpu block, gets hot and then enters the second cpu block.