IN EEN BOORKOLOM AANGEBRACHTE HULP-GESTUURDE KLEP.

摘要

An auxiliary controlled valve including a valve body (8) displaceable against a valve seat (9) disposed in a drilling string (6) to produce pressure pulses in drilling fluid renders possible a selective closing or opening of a low-resistance transmission section (12) which lies parallel to a main throttle section (10). The valve has a central passage which permits the passage of measuring instruments through the valve regardless of the particular position of a valve body (8). The valve body (8) is largely balanced out with regard to dynamic flow forces so that only a comparatively small actuating force is necessary.