Pump Stroke Control for Gradient Chromatography Flow Stability
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Solution Overview
Problem
High pressure gradient liquid chromatography systems face disturbances and inaccuracies in solvent composition due to pump refilling processes, leading to overlapping flow rate variations and compositional inaccuracies in the delivered mobile phase.
Innovation Solution
The method involves synchronizing pump strokes of multiple solvent pumps at the same frequency with offset initiations to prevent overlapping flow rate variations, ensuring accurate composition gradients by interspersing pump strokes and adjusting volume contributions based on a predetermined gradient.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If pump refilling is performed periodically to maintain constant fluid flow, then the pump can sustain continuous operation, but flow disturbances and pressure ripples occur during refilling
Solution Approach 1:
The system performs preliminary refilling of pump heads during periods when the other pump is delivering fluid, ensuring that refilling operations are completed before they would cause overlapping disturbances. This advance preparation maintains continuous operation while preventing flow instability.
Solution Approach 2:
The patent implements periodic refilling cycles for each pump head, alternating between the two pumps in a coordinated manner. By establishing regular periodic action with offset timing, the system maintains continuous operation while distributing refilling disturbances across different time periods, preventing overlapping disruptions.
2Adaptability or versatility
If multiple pumps operate in parallel to deliver multiple fluids, then the system can achieve specified final fluid composition, but overlapping refilling causes composition inaccuracies
Solution Approach 1:
The control system anticipates potential overlapping refilling events and schedules refilling operations in advance to occur during periods when the other pump is in its delivery phase. This preliminary coordination ensures that composition gradients are established accurately without contamination from simultaneous refilling disturbances.
Solution Approach 2:
The system dynamically adjusts the timing and scheduling of refilling operations based on the operational state of each pump. By making the refilling schedule adaptive rather than fixed, the system can maintain precise composition control while accommodating the dynamic needs of parallel pump operations.
3Productivity
If pump refilling occurs during pressure disturbances from another pump, then continuous fluid delivery is maintained, but solvent composition does not match desired composition
Solution Approach 1:
The system schedules refilling operations to occur in advance during periods of stable pressure and flow from the other pump, preventing refilling from occurring during pressure disturbances. This preliminary timing ensures both continuous delivery and composition accuracy.
Solution Approach 2:
The control system creates temporal separation between refilling operations and pressure disturbance periods, cushioning the system against composition errors by ensuring refilling occurs during stable conditions. This beforehand cushioning prevents the harmful overlap of refilling and pressure disturbances.
Data Source
AI summary
Described is a method of generating a flow having a composition gradient such as a mobile phase gradient for liquid chromatography. A pair of pumps is operated such that the initiations of pump strokes for one pump are controlled to occur between the initiations of pump strokes for the other pump so that the sequences of pump strokes fort the two pumps are interspersed in time. Initiations of the pump strokes of the second pump are offset in time relative to initiations of the pump strokes of the first pump such that variations in the flow rates of the first and second pumps due to initiation do not overlap in time. The volume of liquid contributed by a pump stroke is controlled according to the relative contribution of the respective pump to the composition gradient.