Abstract: A valve apparatus adapted for connection in a drill stem comprises a sleeve member slidably guided in a body having a longitudinal fluid passage and lateral openings that communicate with an annular space surrounding the sleeve member. The sleeve member also comprises lateral holes of small diameter and bottom orifices or channels of large diameter. In a first position of the sleeve member, the fluid flows from the drill stem towards the annular space through the holes of small diameter. When the rate of flow reaches a sufficient value, the sleeve member is moved against a biasing spring to a second position, where the small holes are closed and the large channels permit the passage of the fluid through the valve, towards the lower part of the drill stem, without any noticeable pressure drop. The sleeve member is retained in the said second position through the pressures in the drill stem and in the annular space acting on different areas of the sleeve member.

Abstract: The process enables, while starting from the same basical members, assembled in two different arrangements, to drive an earth-boring tool such as a bit, a milling cutter, a core barrel or the like with a reduced speed or a fast speed, according to the prevailing boring conditions. The downhole motor comprises a shaft and a body constituted by two helicoidal gears arranged within each other, providing an encapsulation preferably of right-handed pitch and having K and K+1 teeth. For providing a reduced speed the body is rotatably mounted and the tool is connected to said body. The shaft is angularly fixed and free to undergo a nutation movement. The resulting speed is the relative speed of rotation between the said body and the said shaft. For providing a fast rotation speed, the body is angularly and radially fixed. The helicoidal shaft meshes with the body and is supported in order freely to rotate around a crank system. The tool is connected to the crank.