Pressure Control Valve Minimizing Dead Volume in SFC
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Solution Overview
Problem
In supercritical fluid chromatography (SFC), existing pressure control valves have significant dead volume, which leads to stagnation of the mobile phase and mixing of separated components, impairing analysis accuracy when connected to mass spectrometry (MS), particularly due to high pressures and small flow rates.
Innovation Solution
A pressure control valve design with a minimal dead volume, utilizing a valve body made of chemically and pressure-resistant materials like PBT or PEEK, and an elastic sealing member with a protective film, along with a cylindrical bore hole and thread engagement for precise pressure control, minimizing internal volume and preventing component mixing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional pressure control valve structure is used, then pressure control function is achieved, but dead volume increases causing mobile phase stagnation and component mixing
Solution Approach 1:
The invention extracts and eliminates the unnecessary large-volume control chamber from conventional diaphragm valves. By removing the traditional diaphragm structure and large control chamber, the patent creates a compact pressure control valve with minimal dead volume that maintains effective pressure control while preventing mobile phase stagnation and component mixing.
Solution Approach 2:
The pressure control valve is segmented into compact functional components: a valve body with precisely positioned inlet and outlet channels, a needle valve mechanism for pressure control, and integrated sealing structures. This segmentation allows each component to perform its function efficiently within a minimal volume, eliminating the large control chamber of conventional designs.
2Stress or pressure
If high pressure (10 MPa or more) is applied to achieve supercritical state, then supercritical fluid properties are obtained, but sealing difficulty at insertion portions increases
Solution Approach 1:
The invention employs flexible sealing members including O-rings and elastic sealing elements at the insertion portions where inlet and outlet tubes connect to the valve body. These flexible sealing components deform under high pressure (10 MPa or more) to maintain contact and sealing, ensuring reliable sealing performance under supercritical conditions without requiring complex sealing structures.
Solution Approach 2:
The valve body is constructed from chemically and pressure-resistant materials such as PBT (polybutylene terephthalate) or PEEK (polyether ether ketone) that can withstand high pressures (10 MPa or more) and resist degradation from supercritical carbon dioxide and mobile phase chemicals. These composite material properties ensure structural integrity and sealing reliability under extreme operating conditions.
3Stress or pressure
If valve tube is completely flattened to achieve high pressure control, then pressure control is improved, but opening area becomes extremely small (0.001 mm²)
Solution Approach 1:
The needle valve mechanism provides dynamic control of the opening area between the needle and the orifice opening. By adjusting the insertion depth of the needle into the orifice, the opening area can be precisely controlled from fully open to nearly closed positions. This dynamic adjustment allows pressure control across a wide range while maintaining adequate opening area for the required minute flow rate (3 ml/min or less).
Solution Approach 2:
The invention changes the control parameter from complete flattening of the valve tube to needle insertion depth control. This parameter change allows for more precise and gradual pressure control, maintaining a small but non-zero opening area that accommodates the minute flow rate requirements of SFC while achieving the necessary pressure control precision for supercritical conditions.
4Volume of stationary object
If internal volume of control chamber is reduced to prevent dead volume, then component mixing is prevented, but manufacturing precision requirements increase
Solution Approach 1:
The inlet channel, outlet channel, and pressure control mechanism are merged into a single integrated valve body structure. The inlet channel is positioned at the center of the valve body, with the outlet channel and needle valve mechanism arranged in close proximity. This merging eliminates the need for large control chambers and complex assembly, reducing internal volume while maintaining manufacturability through integrated design.
Solution Approach 2:
The valve body employs asymmetric channel positioning with the inlet channel at the center and the outlet channel offset to one side, optimized for minimal internal volume. The needle valve is positioned asymmetrically to achieve the required pressure control function with minimal clearance volumes. This asymmetric design reduces dead volume while maintaining adequate sealing and control functions.
Data Source
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AI summary
A pressure control valve includes a pressure control block including a bore hole that is bored perpendicularly from one outer surface, and two internal channel openings of whose end portions are at a bottom surface of the bore hole, a valve body having elasticity and covering the bottom surface of the bore hole, a sealing member for pressing a portion of the valve body against the bottom surface of the bore hole, the portion abutting a peripheral edge portion of a portion of the bottom surface where the openings are provided, and an actuator for driving a portion, of the valve body, abutting the portion where the openings are provided in a direction perpendicular to the bottom surface of the bore hole.