Fluid that is pumped back to the bit is clean drilling can be done faster with a light
weight fluid than with a heavier liquid the system should also be designed to enable a
large volume of liquid under high pressure to reach the bit. the proper combination of
pump, drill stem nozzles and hole diameter achieves this by enabling about 50 to 60
per cent of the fluid pressure generated by the pump to reach the bit nozzles and clean
the bottom of the hole