Circulation system:

The complete, circuitous path that the drilling fluid travels.

Starting at the main rig pumps, major components include surface piping, the standpipe, the kelly (rotary) hose, the kelly, the drillpipe, drill collars, bit nozzles, the various annular geometries of the openhole and casing strings, the bell nipple, the flowline, the mud-cleaning equipment, the mud tanks, the centrifugal precharge pumps and, finally, the positive displacement main rig pumps.