Reverse circulation drilling system (RCD), also known as air-lift system, is that compressed air is injected into the drill pipe below water level just above the drill bit. This reduces the density of the internal water column and starts the circulation. The mixture of water, air, and cuttings is then flushed out through the drill pipe into settling tanks.Working with RCD rigs are a highly efficient, safe and environmentally friendly solution for drilling large diameters and depths.If there are drilling conditions required as follows:1) Large Diameter (from 0.8 m to 3.3 m)2) Deep Depth (more than 40 m)3) Hard Rock Layer (75 Mpa ~ 250 Mpa)Definitely the most suitable equipment is RCD rig.StabiliserThe stabiliser diameter is decided according to drill bit cutting diameter. To avoid jam inside of casing, the drill bit cutting diameter is recommended to be 100 mm less than casing in-diameter. And stabiliser diameter should be 50 mm less than drill bit cutting diameter.Ex) Casing in-dia 2,000 mm => Drill bit dia 1,900 mm => Stabiliser dia 1,850 mmBUMA stabiliser guide is assembled by bolting to body. Changing by stabiliser guide, it can be applied to different diameter. However, the stabiliser guide needs to be assembled by welding because of diameter limit for each drill pipe (NW200, NW300).NW200 drill pipeStabiliser dia assembled by welding: from 750 mm ~ less than 900 mmStabiliser dia assembled by bolting: from 900 mm ~NW300 drill pipeStabiliser dia assembled by welding: from 1,100 mm ~ less than 1,200 mmStabiliser dia assembled by bolting: from 1,200 mm ~Drill string (Drill pipe)There are two types of drill string (drill pipe) according to internal pipe diameter, NW200 (200 mm) and NW300 (300 mm). NW200 drill pipe can be used up to RCD R1820 because of handling torque limit. Mainly up to drilling dia. 1.5 m, using recommended NW200 drill pipe is recommended.Basic drill string: In order to prevent buckling in the bottom part of casing and for better verticality, Basic drill string is required. The basic drill string is composed of drum stabiliser, heavy duty space pipe, heavy duty stabiliser and reducing pipe.Drill rod pipe stabiliser: In order to prevent bending of drill string and keep verticality, the drill rod pipe stabiliser is used for every three units of drill rod pipe (1 drill rod pipe = 3 m). That means, it is required to install one drill rod pipe stabiliser in every 9 m.Selection of RCD rigAccording to drilling diameter required, one needs to choose RCD rig.From dia 800 mm to 2,000 mm, customers prefer to use RCD R1820.From 2,000 mm to 3,000 mm customers prefer to use RCD R3030.Selection of clamping deviceRCD rig is operated on the top of the casing.For the stable and safe operation of the drilling rig, the clamping device is holding the casing.To prevent deforming when it clamps casing, the wall thickness of the clamping section (top 2~3m of casing) must be at least than 25 mm.