Syringe Plunger Rod Thread Venting for Piston Cavity Sterilization
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Solution Overview
Problem
Standard plunger rods in syringes often fail to facilitate effective decontamination of the piston cavity surfaces, which can lead to contamination issues during use.
Innovation Solution
A plunger rod design with a threaded extension that creates ventilation spaces between the threaded extension and the piston cavity, allowing for sterilizing fluids to pass through and sterilize the piston cavity, combined with auxiliary passages for enhanced fluid flow.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional thread geometry with root clearance is used, then manufacturing is easier, but stress concentration occurs at the root of the internal thread
Solution Approach 1:
The patent modifies the geometric parameters of the thread by eliminating root clearance and using complementary thread forms (square, rectangular, triangular, or trapezoidal profiles) where the internal and external threads fit together without gaps. This parameter change eliminates stress concentration while maintaining manufacturability through precise machining processes.
2Ease of repair
If plunger rod assembly is disassembled for maintenance, then repairs can be performed, but bacteria can enter and contaminate the wellbore
Solution Approach 1:
The plunger rod is designed with the internal thread nested within the plunger body and the external thread on the rod end, creating a telescoping assembly that can be inserted and removed as a unit. This nesting allows maintenance without disassembly, preventing bacterial entry while enabling repair through simple insertion/removal operations.
Solution Approach 2:
The assembly is segmented into modular components (plunger rod, packing, seal elements) that can be independently replaced by removing and reinserting the entire plunger rod assembly, avoiding the need to open the wellbore equipment and eliminating contamination risk during maintenance.
3Ease of repair
If plunger rod assembly is inserted and removed frequently, then maintenance is enabled, but wear occurs at the interface between packing and rod
Solution Approach 1:
The packing element is extracted as a separate replaceable component that can be removed and replaced without affecting the plunger rod. This allows the wear-prone packing to be periodically renewed while the rod maintains its precise thread geometry, separating the wear function from the structural function.
Solution Approach 2:
The packing is constructed from composite materials combining elastomeric matrices with abrasion-resistant particles or reinforcement, providing both flexibility for sealing and enhanced wear resistance for repeated insertion/removal cycles at the rod interface.
Data Source
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AI summary
A fluid-dispensing syringe includes a barrel and a plunger assembly disposed within the barrel. The assembly includes a piston with an outer piston surface, an inner piston cavity with an inner piston surface and at least one female thread, and proximal and distal piston ends. The plunger rod includes a rod body having proximal and distal rod ends, with a threaded extension extending distally from the distal rod end. The threaded extension extends distally along a distal length and threadedly engages the at least one female thread along a portion of the distal length. The threaded extension has a ventilation feature configured to create a ventilation space between the threaded extension and the inner piston surface. The proximal piston end and the distal rod end are in spaced relation to form a primary fluid passageway portion from outside of the plunger assembly into the piston cavity.