Fluid End Nut Retention to Prevent Preload Loss and Face Cracks
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Solution Overview
Problem
Reciprocating pumps suffer from face cracks around the preload-applying nut due to pressure pulse-induced vibrations, which cause the nut to rotate and reduce the tensile preload, leading to thread fatigue and eventual cracking.
Innovation Solution
A fluid end assembly with a retainer, such as a retaining ring, tabs, or spring-loaded detents, is used to restrict the nut's rotation relative to the body, maintaining compressive and tensile preloads and preventing face cracks by ensuring the nut remains engaged with the threads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the nut is allowed to rotate freely under pressure pulse-induced vibrations, then the assembly is simpler without additional anti-rotation components, but the nut backs out from threads causing loss of tensile preload and face cracks
Solution Approach 1:
The nut is segmented into two functional parts: a threaded portion that engages with the body to maintain tensile preload, and a split end with tabs that can be restrained by a retainer. This segmentation allows the nut to simultaneously provide clamping force and anti-rotation capability, resolving the contradiction between reliability and device complexity.
Solution Approach 2:
A retainer (such as a retaining ring, tabs, or spring-loaded detents) is introduced as an intermediary component between the nut and the body. This retainer restricts rotation of the nut without interfering with the threaded engagement, thereby maintaining preload while preventing back-out caused by vibrations.
2Strength
If the nut is tightly secured to prevent rotation, then face cracks are prevented, but the assembly becomes more complex requiring additional retaining components
Solution Approach 1:
The anti-rotation function is merged with the existing nut structure through the split end design. The tabs on the split end can be directly restrained by simple retainers already present in the assembly, combining the fastening and anti-rotation functions into a unified system that enhances structural integrity without significantly increasing complexity.
Solution Approach 2:
Instead of trying to make the nut itself resistant to rotation through complex threading or locking mechanisms, the solution inverts the approach by using the split end tabs as the primary anti-rotation feature. This simpler tab-based approach, restrained by minimal retainers, achieves the same structural integrity goal with less complexity.
3Device complexity
If the nut rotates under vibration, then the assembly structure remains simple, but thread fatigue occurs leading to eventual cracking
Solution Approach 1:
The split end with tabs is designed in advance to engage with retainers that prevent rotation. This preliminary anti-rotation design ensures that before vibration-induced back-out can occur, the nut is already restrained, thereby preventing thread fatigue and extending service life without complicating the overall assembly structure.
Solution Approach 2:
The vibration that would normally cause harmful back-out and thread fatigue is countered by the split end tabs that convert the vibration energy into a beneficial locking action. The tabs engage with the retainer under vibrational loads, transforming the harmful oscillation into a self-reinforcing anti-rotation mechanism that extends component life.
Data Source
AI summary
The present disclosure relates to reciprocating pumps, such as to fluid end assemblies of reciprocated pumps. In a first aspect, a fluid end assembly includes a body defining a bore and including at least one first thread. The assembly further includes a cover capable of being disposed within the bore, a nut including at least one second thread, and a retainer capable of being disposed relative to the nut such that the retainer restricts the nut from rotating relative to the body. The at least one second thread can engage with the at least one first thread such that, when the at least one second thread is engaged with the at least one first thread, the nut applies compressive force to the cover. Other aspects and features are also claimed and described.