Self-adjusting automatic locking piston for RAM blowout preventers

摘要

An improved self-locking piston for use in ram blowout preventers has a hollow cylindrical outer piston which slidably contains an inner locking piston. The inner locking piston has a tapered, frusto-conically shaped front section with a plurality of circumferentially spaced apart, sloping flats formed therein. Apertures provided through the outer wall surface of the main outer piston contain radially slidable driver segments each having a sloping surface complementary to the sloping surface of the flats on the inner piston. Forward motion of the inner piston relative to the outer piston forces the driver segments radially outwards in the apertures. A plurality of locking segments, one each positioned in a groove rearward of and communicating with a separate one of each of the apertures is provided. Each locking segment has a sloping lower front surface adapted to sliding engagement by the sloping upper rear surface of a driver segment. Outward radial motion of the driver segments causes the locking segments to move into locking engagement with an annular groove provided in the inner wall surface of the ram cylinder. Each rear locking segment groove is longer than that of the rear portion of a locking segment. Thus, locking segments may move rearward in their grooves, permitting forward motion of the inner piston, outer piston, piston rod, and ram sealing element to compensate for ram rubber wear while still maintaining the ram sealing element firmly locked in its forward-most sealing position.