A method and apparatus for changing the speed of a
drill bit down hole in a fluid-actuated motor, including a positive displacement motor and a
hydraulic motor, is disclosed. The apparatus comprises a
bypass valve installed in the motor for controlling flow through and around the power section of the motor. When closed, the
bypass valve forces all fluid to flow through the power section of the motor, imparting maximum speed to the
drill bit. When opened, a portion of the fluid flow is allowed to flow around the power section of the motor, thereby reducing the speed of the
drill bit. The
bypass valve may be opened or closed mechanically, electrically, hydraulically, pneumatically, or by any other means, including a removable plug.