Self-aligning stuffing box with oversized apertures
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Solution Overview
Problem
Conventional stuffing boxes face issues with misalignment of the polished rod, leading to excessive wear, leaks, and potential wellbore safety risks due to side loads on seals, and existing adjustable designs either compromise on pressure rating or require specialty components.
Innovation Solution
A self-aligning stuffing box with a laterally adjustable upper sealing section and annular bushings that can accommodate misalignment without subjecting seals to excessive side loads, featuring oversized apertures for flanged connections and annular bushings to constrain and align the polished rod, allowing for high-pressure operation with commonly available components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional stuffing box is used, then the structure is simple and manufacturing is easy, but the polished rod misalignment causes excessive seal wear and leakage
Solution Approach 1:
The stuffing box incorporates a laterally adjustable upper sealing section that can be displaced relative to the lower section to align with misaligned polished rods. This dynamic adjustment capability allows the sealing section to adapt to rod misalignment, preventing excessive seal wear and leakage while maintaining a relatively simple overall structure.
Solution Approach 2:
The stuffing box is divided into a lower section and an upper sealing section that can be independently positioned. The lower section remains fixed while the upper sealing section can be laterally adjusted to align with the polished rod, allowing the sealing function to be separated from the mounting function and resolved independently.
2Reliability
If an adjustable stuffing box with angular alignment interface is used, then alignment with misaligned rods is improved, but the device height increases and pressure rating decreases
Solution Approach 1:
The adjustable stuffing box uses a dynamic lateral adjustment mechanism where the upper sealing section can be displaced horizontally relative to the lower section through oversized apertures and washers, rather than requiring a tall angular alignment interface. This maintains a compact height while achieving alignment capability.
Solution Approach 2:
The design changes the alignment parameter from vertical/angular displacement to horizontal/lateral displacement. By allowing lateral movement of the sealing section through oversized apertures with washers, the system achieves alignment capability without increasing height, thereby maintaining compact dimensions and pressure rating.
3Adaptability or versatility
If oversized bolt holes are used for lateral adjustment, then alignment range is improved, but flange size and component complexity increase
Solution Approach 1:
Oversized washers are introduced as intermediary elements between the bolts and the flange. These washers allow lateral displacement of the sealing section through the oversized apertures while distributing the load and enabling alignment adjustment without requiring larger or more complex flange structures.
Solution Approach 2:
The connection system transitions from a rigid fixed-hole bolt connection to a dynamic adjustable connection using oversized apertures with washers. This allows the connection to adapt laterally during assembly for alignment, then maintains structural integrity when tightened, providing both adjustability and strength.
4Reliability
If the sealing section is laterally displaced for alignment, then alignment with misaligned rods is achieved, but the fastening stability must be maintained
Solution Approach 1:
The fastening system operates in two states: during alignment, the oversized apertures allow lateral displacement of the sealing section; during operation, the tightened fasteners constrain the section to maintain alignment. This dynamic transition ensures both alignment capability and fastening stability are achieved.
Solution Approach 2:
The alignment adjustment is performed preliminarily during assembly before the fasteners are fully tightened. Once the sealing section is laterally displaced to achieve proper alignment with the polished rod, the fasteners are then secured to lock the position, ensuring both alignment accuracy and fastening stability.
Data Source
AI summary
A self-aligning stuffing box is provided for mounting to a wellhead and aligning with a polished rod extending therethrough. The stuffing box has an upper sealing section housing stuffing box seals and an annular retaining plate for clamping a flange portion of the sealing section to the wellhead. The flanged portion of the sealing section has oversized bolt apertures, allowing it to be laterally displaced relative to the wellhead before being secured to the wellhead. The retaining plate and the wellhead have bolt apertures corresponding to the oversized apertures. The stuffing box can be mounted on a wellhead using a plurality of fasteners. The stuffing box can be aligned with a polished rod by loosening the fasteners and stroking the polished rod to allow the sealing section to be laterally displaced. The fasteners can then be tightened or re-tightened to secure the sealing section to the wellhead.