Clamshell Wristpin Retainer for Safer Rod Pump Installation

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Solution Overview

Problem

Conventional wrist pin nuts for connecting pitman arms to crank arms in reciprocating pump units are difficult to install, prone to galling and corrosion, and require large hammer wrenches for tightening, making them hazardous and strenuous to use.

Innovation Solution

A clamp-based retainer system with spacers and tensioning bolts is used to connect the pitman arm to the crank arm, allowing for easy installation and secure attachment without the need for a hammer wrench, and is resistant to galling and corrosion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If a conventional wrist pin nut is used to connect the pitman arm to the crank arm, then the connection is secure, but the installation is difficult and requires large hammer wrenches

Engineering Contradiction:

Improveease of installationVSAvoidtool requirement

Core Design Contradiction:

Ease of operationVSDevice complexity

Solution Approach 1:

The retainer is divided into two separate halves that can be independently positioned and secured. This segmentation allows the retainers to be installed without requiring large hammer wrenches, as each half can be separately attached to the wrist pin end, simplifying the installation process while maintaining secure connection.

Inventive Principle:

Principle #1Segmentation

2Reliability

If a conventional wrist pin nut is used, then the connection is secure, but the nut is prone to galling and corrosion

Engineering Contradiction:

Improveconnection securityVSAvoidgalling and corrosion

Core Design Contradiction:

ReliabilityVSObject-affected harmful factors

Solution Approach 1:

The invention extracts the problematic threaded nut component from the connection system and replaces it with a clamp-style retainer that secures the wrist pin end through mechanical clamping force. This eliminates the threaded interface that is susceptible to galling and corrosion, while maintaining secure connection through the retainer's clamping action on the wrist pin end.

Inventive Principle:

Principle #2Taking out (Extraction)

3Strength

If a conventional wrist pin nut is used, then the connection is secure, but the installation is strenuous and hazardous

Engineering Contradiction:

Improveconnection strengthVSAvoidinstallation difficulty

Core Design Contradiction:

StrengthVSEase of operation

Solution Approach 1:

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of using a nut that threads onto the wrist pin end from the inside of the crank arm, the invention uses retainers that clamp onto the outside of the wrist pin end. This inverted approach eliminates the need for threading operations and large wrenches, making installation less strenuous and hazardous while maintaining connection strength.

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS12595791B2Multi-bolt clamshell retainer for wristpin on rod pump unit

Publication Date: 2026.04.07 TRC SERVICES INC

AI summary

An assembly connects a pitman arm to a slot in a crank arm of a pumping unit. A pin extends from the pitman arm disposed on a first side of the crank arm. The pin is disposed in the slot of the crank arm and has a distal end exposed on a second side of the crank arm. The distal end defines an external shouldered profile. A clamp is positioned on the distal end of the pin. The clamp has an internal shouldered profile, which is configured to engage the external shouldered profile on the pin. One or more spacers are disposed on the clamp and are configured to adjustably extend from the clamp toward the second side of the crank arm.