Plug Valve Indicator Shear Key Failure
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Solution Overview
Problem
In hydraulic fracturing operations, high fluid pressures can cause shear keys in plug valve drive mechanisms to fail, leading to incorrect indications of valve position due to the indicator continuing to rotate with the drive sleeve after the shear key shears, despite the valve element not rotating.
Innovation Solution
A plug valve design where the indicator is fixed to the drive output member, ensuring it rotates only with the valve element, providing accurate position indication regardless of shear key failure, with indicia on the housing face and a pointer on the indicator plate to clearly show open or closed positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the indicator is mounted to the drive sleeve to indicate valve position, then the indicator can show the position, but the indicator may indicate an erroneous position when the shear key shears due to excessive force
Solution Approach 1:
The system is segmented into two independent rotational indicators: one mounted to the drive sleeve (showing drive mechanism rotation) and one mounted to the valve element (showing actual valve position). This segmentation allows the system to distinguish between drive mechanism rotation and actual valve element rotation, preventing erroneous readings when the shear key fails.
Solution Approach 2:
A second indicator mounted to the valve element acts as an intermediary reference that directly reflects the valve element's position regardless of drive mechanism status. This intermediary indicator provides a reliable reference point that mediates between the drive sleeve indicator and the actual valve position, ensuring accurate indication even when the shear key shears.
2Strength
If a shear key is used to connect the drive shaft and drive sleeve, then the drive mechanism can protect against excessive force, but the indicator becomes unreliable when the shear key fails
Solution Approach 1:
The indication system is segmented into two independent indicators: one on the drive sleeve and one on the valve element. This segmentation allows the system to maintain accurate position indication through the valve element-mounted indicator even when the shear key fails and the drive sleeve becomes decoupled from the drive shaft.
Solution Approach 2:
The indicator mounted to the valve element serves as an intermediary that directly reflects the valve element's actual position. This intermediary indicator bypasses the potentially failed shear key connection and provides reliable position information regardless of the drive mechanism's mechanical integrity.
3Ease of operation
If the indicator rotates with the drive sleeve, then it can indicate position changes, but it continues to rotate after the shear key shears causing erroneous readings
Solution Approach 1:
The indication system is divided into two separate indicators with independent rotation: one on the drive sleeve and one on the valve element. This segmentation ensures that the valve element-mounted indicator rotates only with the valve element, providing accurate position information even when the drive sleeve rotates independently after shear key failure.
Solution Approach 2:
The indicator mounted to the valve element acts as an intermediary that directly tracks the valve element's position without being influenced by drive sleeve rotation. This intermediary indicator provides a reliable reference that mediates between the drive mechanism's motion and the actual valve position, preventing erroneous readings.
Data Source
AI summary
A valve has a body having a rotatable valve element. A drive mechanism has a drive input member and a drive output member that are coupled to the valve element for rotating the valve element. A shear member is operatively located within the drive mechanism between the drive input member and the drive output member for shearing in the event the force to rotate the valve element is excessive. The valve has indicia indicating open and closed positions for the valve element. An indicator is mounted to output drive member to properly align with the indicia regardless whether the shear member has sheared or not.