Capillary Tube Plug Sealing to Eliminate HPLC Dead Volume
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Solution Overview
Problem
Existing connection systems for capillary tubes in high-performance liquid chromatography suffer from dead volume issues due to misalignment of sealing elements, deformation of capillary tubes, and difficulty in adapting to different diameters and tolerances, leading to unreliable connections and potential damage.
Innovation Solution
A plug unit with a sealing element and pressure piece design that ensures the sealing element is flush or slightly projects past the capillary tube end surface, allowing for axial pressure transmission to create a pressure-tight seal without dead volume, and can be adapted to different bushing unit diameters by selecting the appropriate outer diameter for the sealing element or pressure piece.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If sealing elements are pressed into a conical receptacle opening to create a tight connection under high pressure, then sealing reliability is improved, but the sealing position is offset rearward from the capillary tube end surface, creating dead volume
Solution Approach 1:
Instead of pressing the sealing element into a conical receptacle opening from the front (conventional approach), the invention inverts the approach by having the capillary tube end surface itself contact the floor wall of the receptacle opening directly. The sealing element is positioned to be surrounded by the pressure piece rather than being pressed into a conical space, reversing the traditional sealing mechanism to eliminate dead volume while maintaining sealing reliability under high pressure.
2Reliability
If an attachment screw exerts extremely high radial pressure on the sealing element to guarantee tightness, then sealing reliability is improved, but the sealing element and capillary tube deform, creating a positive-fit connection that prevents easy reconnection
Solution Approach 1:
The invention segments the connection functions by separating the sealing function from the fixing function. The capillary tube end surface provides the primary sealing contact with the floor wall, while the pressure piece and attachment screw provide the clamping force. This segmentation allows the sealing interface to remain undeformed and reusable, eliminating the need for extreme radial pressure that causes deformation and prevents reconnection.
Solution Approach 2:
The pressure piece acts as an intermediary element between the attachment screw and the sealing interface. Instead of the attachment screw directly pressing the sealing element into deformation, the pressure piece distributes the clamping force uniformly, allowing the sealing to occur at the capillary tube end surface without the harmful radial compression that causes permanent deformation and prevents easy reconnection.
3Reliability
If the sealing element is made with a conical profile to interact with a conical receptacle opening, then sealing reliability under high pressure is improved, but the connection system lacks adaptability to different bushing unit diameters and tolerances
Solution Approach 1:
The invention creates a universal connection system where the capillary tube end surface serves as the universal sealing interface for all bushing units. By eliminating the conical profile requirement and using a flat end surface contact with the floor wall, the system becomes adaptable to different bushing unit diameters and tolerances while maintaining sealing reliability. The pressure piece and attachment screw mechanism provides the necessary clamping force universally across different configurations.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enables reliable, pressure-tight connections with minimal or no dead volume, allowing for easy reconnection and adaptation to various bushing units, preventing sealing element detachment and reducing the risk of capillary tube deformation or damage.
Implementation Method 1
an axial pressure force is transmitted via the pressure piece onto the sealing element and the plug capillary tube. Here, first, the plug capillary tube is fixed in the receptacle opening of the bushing unit due to the rigid attachment of the pressure piece and the sealing element on the plug capillary tube, and second, a pressure-tight seal with little or no dead volume is created in the region of the end surface of the plug capillary tube or the sealing element by the compression of the sealing element
Data Source
AI summary
A plug unit for connecting capillary tubes includes a plug housing that has an axial borehole, a plug capillary tube that projects through the axial borehole, and a sealing element that surrounds the plug capillary tube. The front end of the plug capillary tube is sealed by an elastic and/or plastic deformation of the sealing element against the capillary tube receptacle opening of a bushing unit. A hollow cylindrical pressure piece is provided that surrounds the sealing element in an axial region facing away from the end surface of the plug capillary tube, and the pressure piece has a rearward end side that faces away from the end surface of the plug capillary tube and that can be loaded by the plug housing with an axial pressure force when the plug unit and bushing unit are connected.