What Is Back Pressure?
In the use of syringe pump systems several characteristics should be considered according to each application. Especially for low flow applications, the performance will depend on the right setup choice, excessive back pressure and inefficient power should be avoided2. The back pressure is defined as a resistant pressure exerted by a liquid or gas against the forward motion or flow of an exhaust or pipe system. The back pressure is very important since the high back pressure is one of the main causes of stalls of syringe pumps.
Back Pressure Control
For the control of the back pressure, some factor such as fluid viscosity, flow rate, tubing diameter, and distance should be considered. The selection of the type of syringe is also crucial to controlling the back pressure 3. To avoid stalls due to back pressure for high viscosity fluids the material of the syringe has to be not deformable and resistant to high pressures, in this case stainless steel is preferred. However, its application for low flow applications is limited due to typically they do not come in sizes smaller than 5 mL. In the case of tubing selection, larger inner diameters and shorter length tubing should be used to minimize back pressure problems. When low flows are necessary for the application, a high-quality back pump pressure regulator is recommended to prevent fluctuation in the outflow.
Back Pressure Cases
Typically, continuous flow systems operate with back-pressure regulators. In other words, if reactor tubing has leaks or breaks operating a 150 psi of back pressure; the content will be released with 150 psi of pressure. The practical outcome of back pressure operation is that solvents can be heated above their atmospheric boiling points. The operation under back pressure regime is justified by the reaction kinetics enhancements which is reached with solvent evaporation.
Chemyx offers the option to control high-pressure dosing applications without a back-pressure modulator. The Chemyx Fusion 6000 high-pressure syringe pump is able to dose viscous solutions against pressure (which also can allow volatilization for pack-bed reactors). Additionally, the machined stainless-steel syringes are robust and perfect for back pressure applications, especially in continuous systems.
- Britton, J., & Jamison, T. F. (2017). The assembly and use of continuous flow systems for chemical synthesis.Nature Protocols, 12(11), 2423–2446. https://doi.org/10.1038/nprot.2017.102
- Chemyx. (2017a). The syringe pump stalls during a run. Retrieved from https://www.chemyx.com/support/knowledge-base/technical-support/troubleshooting-syringe-pump/
- Chemyx. (2017b). Selecting a Type of Syringe. Retrieved from https://www.chemyx.com/support/knowledge-base/getting-started/selecting-a-syringe/