PRESSURE DRIVEN FLOW CONTROL
How to perform ultra-precise and responsive flow control thanks to a pressure controller?
For historical reasons syringe pump is the most used system in microfluidics. However, researchers are starting to switch to pressure control systems because their unique performances enhance experiments.
In this document we will explain how pressure driven flow control works, the advantages / disadvantages of the different technologies and how to choose between a syringe pump and pressure control depending of your requirements.
List of components
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SETUP DIAGRAM : Turn your system into a powerful syringe pump
Pressure driven flow control is a smart alternative to syringe pump. It allows pulseless flow within subsec response time. It consists in using a gas input pressure within a hermetic liquid tank in order to flow liquid from the tank to your microfluidic device.
Flow control principle
A pressure controller pressurizes a tank, such as Eppendorf, Falcon or a bottle containing the sample, which is then smoothly and quasi-instantly injected into a microfluidic chip.
figure 3 : The reservoir is pressurized, the gas pushes on the fluid surface, the fluid will flow through the outlet. Thus, controlling the input gas pressure of the tank will enable to control the liquid that flows out of the tank. Thanks to piezoelectric pressure regulation, Elveflow’s system are able to regulate flow within 40 ms with a 0.005 % stability. One advantage of pressure driven flow control relies in the ability to handle fluid volumes of several hundreds of mL. You can thus turn your system into a powerful syringe pump.
By coupling our pressure controller with one of our flow sensor, you can perform ultra precise and responsive flow control. You can request a flow rate value in the Elveflow Software and the pressure controller will automatically adjust pressure to reach the requested value thanks to a customizable PID Feedback loop.
advantages / weakness
Figure 3: pressurized reservoir
- Fast setup for fluidic experiments.
- The amount of dispensed liquid can be known for long term experiment.
- Maximum pressure generated by a syringe pump can be at several hundred bars.
- Fast response time (down to 40ms)
- High stability and pulsless flow
- Possibility to handle fluid volumes of several liters
- Possibility to control fluids in dead-end channels
- Enable both flow and pressure control when used with a flow meter
- Response time (1)
- Knowledge of the real time flow rate (2)
- Limited volume dispensed (3)
- Pulses (4)
- Device destruction (5)
- No pressure measurement (6)
- Dead-end channels (7)
- 8 bar maximum
- Possible BackFlows (8)
(1) Response time can vary from seconds to hours depending on the fluidic resistance and compliance.
(2) Without flow meters, users cannot know the real flow rate during the transient period (seconds to hours).
(3) The amount of fluid dispensed by the syringe pump is limited in volume.
(4) Even pulseless syringe pumps require to carefully choose the syringe size depending on your experimental conditions to avoid periodic pulsations on the flow rate due to the step-by-step motor of the syringe pump.
(5) If channel clogging (dust for example) the pressure increases without limit and can lead to the device destruction.
(6) Knowing the pressure inside the fluidic system requires a pressure sensor.
(7) Flow control of fluids in dead-end channels (like integrated valves) is impossible using syringe pumps.
(8) When pressure is unbalanced, it is possible to have back flows, when doing flow switches with multiple inputs (association with valves is required to solve that problem)
Performance : Syringe Pump VS Pressure Control
The main advantage of syringes pump is that they are quite easy to use, and the two main drawbacks of syringe pumps in microfluidics are slow response times when setting a new flow rate and flow oscillations due to motor steps. Flow changes inside chips can take seconds to hours (see our tutorial on syringe pump responsiveness in microfluidics). This lack of reactivity is one of the main limitations of syringe pumps for numerous applications.
Modern microfluidic pressure controllers also enable you to control both pressure and flow rate by integrating a flow meter with a feedback loop. Microfluidic researchers mainly use pressure controllers when they require high flow responsiveness and high flow stability and precision, as well as when they work with dead-end channels or require large sample volumes.
Response Time & Stability
OB1 flow control in action
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