| 摘要 |
A lockdown screw having a gland nut threaded into a radially extending bore in a head. The radial bore is threaded only so far as to accommodate the gland nut. A stem is threaded into the gland nut for reciprocation into or out of the main bore of the head. The threads on the stem and in the gland nut are the sole working threads of the lockdown screw. A self-energizing packing is disposed around the stem for sealing between the stem and the radial bore. There is zero extrusion gap between the gland nut and the radial bore, adjacent and outwardly of the packing. A step shoulder on the stem carries the packing with it when the stem is removed from the head. An annular backseat shoulder on the stem is engageable with an annular backseat in the gland nut, forming a metal-to-metal seal, in the event of a leak. In the event that the leak is not stopped by actuation of the backseat seal, additional metal-to-metal seals are actuated between the gland nut and the stem, and between the gland nut and the head at the inner and outer ends of the gland nut, by torquing down on the gland nut. |
