Plug mechanism for wellhead tool

A wellhead tool for removing and replacing a valve on an operating wellhead assembly having a housing defining a pressurized chamber, a conduit mounted with the housing and in fluid communication with the pressurized chamber, a fluid coupling on the conduit, and a valve having inlet and outlet fluid couplings with one fluid coupling mounted on the conduit fluid coupling such that the valve is in fluid communication with the pressurized chamber, wherein the wellhead tool comprises:

• an elongated housing having a fluid coupling on one end for engaging a fluid coupling of the valve;
• a plug mechanism for mounting in the conduit to temporarily block fluid flow through said conduit;
• latch means associated with the plug mechanism to temporarily secure the plug mechanism within the conduit of the wellhead assembly;
• a resilient annular sealing member associated with the plug mechanism to temporarily seal off the conduit preventing communication of pressurized fluid from the wellhead to the valve to be removed;
• an operating mechanism carried by the housing and removably connected to the plug mechanism to displace the plug mechanism through the valve into the conduit between the pressurized chamber of the wellhead assembly and the valve to be removed, the operating mechanism operable to expand and release the sealing members and to engage and release the latch means;
• the plug mechanism having a hollow cylindrical body member with an abutment facing one end thereof, the sealing member being positioned adjacent the abutment of the body member in substantially coaxial relationship therewith, a seal retaining member longitudinally slidable into and coaxial with the one end of the body member and having an abutment facing the other side of the sealing member, and an activating shaft rotably mounted in the body member and received through the seal retaining member and operably connected thereto, the activating shaft being operably engageable by the operating mechanism and rotatable to move the seal retaining member longitudinally towards the body member so that the sealing member is compressed between the body member abutment and seal retaining member abutment to radially expand the sealing member;
• and
• the latch means having a latch displacing member mounted on the end of the activating shaft received through the seal retaining member, and a generally cup-shaped end cap received on the end of the seal retaining member, thereby, enclosing the latch displacing member and forming a latch chamber, the end cap having a plurality of slots formed therein communicating from the latch chamber to the exterior circumference of the plug mechanism, the slots having interior walls which are divergently angled toward the central longitudinal axis of the plug mechanism, the latch chamber having a plurality of ball bearings positioned in a surrounding relationship with the activating shaft and being in a free abutting engagement with the activating shaft at all times so that upon rotation of the activating shaft by the operating mechanism the latch displacing member is operable to displace the ball bearings into the slots of the end cap, such that the ball bearings ride or cam along an exterior portion of the latch displacing member between extended and retracted positions.

In an improved wellhead tool of the type used for removing and replacing a valve on an operating wellhead assembly and having an elongated housing with a fluid coupling on one end mountable with a fluid coupling of a valve on the wellhead assembly, a plug mechanism mountable in a conduit communicating to the valve from the wellhead assembly to temporarily block fluid flow through the conduit, an operating mechanism associated with the housing to displace the plug mechanism through the valve and into the conduit and to releasably operate the plug mechanism in the conduit, the plug mechanism having a resilient sealing member associated with the plug mechanism to temporarily seal off the conduit to prevent communication of pressurized fluid from the wellhead assembly to the valve to be removed, wherein the improvement comprises:

• the plug mechanism having a latch means associated therewith to secure the plug mechanism within the conduit of the wellhead assembly against the pressurized fluid existing therein;
• the plug mechanism further including a hollow generally cylindrical body member, a seal retaining member longitudinally slidably mounted on one end of the body member, a threaded activating shaft longitudinally fixed within the body member and threadably received within the seal retaining member and extending therethrough, the activating shaft being operable upon rotation in one direction by the operating mechanism to move the seal retaining member toward the body member, the activating shaft being operable upon rotation in the opposite direction by the operating mechanism to move the seal retaining member away from the body member;
• the latch means having a latch displacing member mounted on the end of the activating shaft extending through the seal retaining member, and a generally cup-shaped end cap received on the end of the seal retaining member, thereby, enclosing the latch displacing member and forming a latch chamber, the end cap having a plurality of slots formed therein communicating between the latch chamber and the exterior circumference of the plug mechanism, the slots having interior walls which are divergently angled toward the central longitudinal axis of the plug mechanism, the latch chamber having a plurality of ball bearings positioned in a surrounding relationship with the activating shaft and being in a free abutting engagement with the activating shaft at all times so that upon rotation in one direction of the activating shaft the seal retaining member and attached end cap are moved towards the body member and latch displacing member to direct one ball bearing into each slot such that the ball bearings ride or cam along an exterior portion of the latch displacing member, the ball bearings being of a sufficiently small diameter to allow the ball bearings to completely enter the slots and sufficiently large diameter to prevent them from completely exiting the slots exteriorly of the plug mechanism, the ball bearings extending beyond the circumference of the plug mechanism when in the extended position to positively secure the plug mechanism within the conduit of the wellhead assembly, the activating shaft being operable upon rotation in the opposite direction to move the seal retaining member and end cap away from the body member and latch displacing member to allow the ball bearings to recede into the slots and latch chamber, thereby, releasing the plug mechanism from the conduit of the wellhead assembly.