Liquid Feeding Device Plunger Speed Control for HPLC Flow Accuracy
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Solution Overview
Problem
The liquid feeding device in HPLC systems faces challenges in accurately controlling the flow rate of the mobile phase due to the compressibility of the mobile phase, leading to deviations in flow rate accuracy, especially when the pressure changes from high pressure in the analysis channel to atmospheric pressure, making it difficult to determine the correct drive speed of the plunger without prior information on the mobile phase's type and compressibility.
Innovation Solution
A liquid feeding device with a discharge channel, pump part, feeding pressure sensor, precompression process execution, discharge speed calculation, and discharge operation controller, which calculates and adjusts the discharge speed of the plunger pumps to maintain a set flow rate under atmospheric pressure by using the detected feeding pressure and compressibility, even without prior knowledge of the mobile phase's type or compressibility, through a precompression process that adjusts the pressure in the pump chamber to match the system pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the primary-side plunger pump performs suction operation with the outlet-side valve closed, then the pressure in the pump chamber decreases, but the liquid feed flow rate temporarily decreases when switching to discharge operation
Solution Approach 1:
The patent applies preliminary action by introducing a precompression operation before the discharge operation. The plunger is driven in the discharge direction during a precompression step to raise the pressure in the pump chamber close to the system pressure before actual discharge begins. This preliminary pressure buildup eliminates the delay in liquid discharge and maintains continuous flow rate, resolving the contradiction between pressure reduction during suction and flow rate maintenance during discharge switching.
2Productivity
If the discharge flow rate is controlled to be a set flow rate, then the volume flow rate at the outlet side of the analytical column becomes larger than the set flow rate due to mobile phase compressibility
Solution Approach 1:
The patent applies feedback by using a pressure sensor to detect the actual pressure in the discharge channel and feeding this information back to the controller. The controller then calculates the compressibility of the mobile phase based on the detected pressure and adjusts the plunger drive speed accordingly. This closed-loop feedback mechanism compensates for the compressibility effect and ensures the volume flow rate at the analytical column outlet matches the set flow rate, resolving the contradiction between discharge flow rate control and volume flow rate accuracy.
3Productivity
If the plunger drive speed is controlled to maintain set flow rate, then the volume flow rate at atmospheric pressure becomes larger than set flow rate due to pressure difference
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the plunger drive speed based on the detected discharge channel pressure. The controller calculates the compressibility and determines the appropriate drive speed to compensate for the pressure difference between high-pressure discharge conditions and atmospheric pressure at the analytical column outlet. This parameter adjustment ensures the volume flow rate at atmospheric pressure matches the set flow rate, resolving the contradiction between maintaining discharge flow rate and achieving accurate volume flow rate measurement.
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
This solution allows for precise control of the plunger drive speed, reducing deviations in the liquid feed flow rate due to mobile phase compressibility, ensuring the volume flow rate at the analytical column outlet matches the set flow rate, even under changing pressures, without requiring information on the mobile phase's type or compressibility.
Implementation Method 1
a precompression operation of driving the plunger in the discharge direction so that the pressure in the pump chamber is raised to a pressure close to the system pressure
Implementation Method 2
a primary-side plunger pump on an upstream side and a secondary-side plunger pump on a downstream side operate in a complementary manner
Data Source
AI summary
The liquid feeding device includes a discharge speed calculation part configured to calculate a discharge speed v of the plunger pump so that a converted value LATM under an atmospheric pressure of a flow rate LPRE of the mobile phase discharged to the discharge channel from the pump part becomes a set flow rate LSET using a volume V of the mobile phase in the pump chamber of the closing pump immediately before the precompression process is started, a volume ΔV reduced due to the precompression process of the mobile phase in the pump chamber of the closing pump, and a feeding pressure P; and a discharge operation controller configured to control a discharge speed of the plunger pump to a discharge speed v calculated by the discharge speed calculation part.