SAFETY SUB Russian patent published in 2008 - IPC E21B17/06 

FIELD: mining, particularly devices to disconnect drilling string in the case of drilling tool jamming used as emergency protection.

SUBSTANCE: safety sub comprises upper 1 and lower 2 subs with central channel 5 connected with each other by means of left-handed thread and thread stop unit movable in axial direction. Stop unit is spring-loaded by means of cylindrical spring 9 and intermediate bush 13 from below. Spline grooves 6 are formed in central sub channel. Outer surface of stop unit and intermediate bush 13 are provided with mating extensions 11, 12. Upper sub 1 spline groove 6 length defined from lower end thereof is equal to length of extensions 11, 12 in stop unit. Cooperating ends of stop unit extensions 11, 12 and intermediate bush 13 are provided with double-sided radial facets. Lengths of grooves 6 formed in lower sub 2 are less than that of extensions 12 of intermediate bush 13.

EFFECT: simplified structure, increased efficiency and operational reliability.

3 cl, 3 dwg