Its purpose is to deflect the downhole motor off vertical to drill a directional hole. See drill stem. This bit consists of a cutting element and a circulating element. The circulating element permits the passage of drilling fluid and utilized the hydraulic force of the fluid stream to improve drilling rates. In rotary drilling, several drill collars are joined to the bottom end of the drill pipe column, and the bit is attached to the end of the string of drill collars.
Most bits used in rotary drilling are roller cone bits, but diamond bits are also used extensively.
It is used in a tubing string where high-velocity flow through perforations may cause external erosion. To bleed down, or bleed off, means to release pressure slowly from a well or from pressurized equipment.