“The reverse circulation drilling is generally used for large diameter piles and consists of returning the drilled material and flushing medium to the surface inside the drill pipes. The pressure and flow of the drilling fluid at, and immediately behind, the drilling bit effectively flushes the drilled material away from the bit and also prevents the borehole from collapsing. Further back from this the hydrostatic head of the drilling fluid ensures the stability of the hole and its viscosity (calculated according to the flow of fluid provided from the drilling rig and the diameter of the hole) must be such as to allow the transport to the surface of the drilled material…”. Text from Massenza Drilling Rigs Website.
Big Bore Reverse Circulation Drilling with a Mayhew SD 54 REV Drilling Rig. Rig manufactured by Drilling Supply & Mfg.; Austin, Texas, USA.