Borehole drilling device

摘要: In order to control the free fall of cement slurry down a borehole casing (10), float shoe (12) at leading end lowermost section, or an annular internal collar in one sections, preferably lowest, is fitted with check valve hold back inflowing until pressure reaches predetermined value. The comprises spring-biassed piston (30) and cross-sectional area flow passage (38) past when open four times inlet (20) valve.