Magma Diaphragm Pump: Performance Data Under Different Pressure Conditions
Applications in bioprocessing may involve liquid transfer to a vessel or disposable container at atmospheric pressure as well as applications such as pumping into a pressurized vessel, a sterilizing grade filter, or a bioreactor. Using the Magma APS-50 data collection feature, data was generated when pumping water into a vessel at atmospheric pressure and against a pressurized vessel. A schematic of the setup is shown in Figure 1. The data in Figure 2 was generated under steady-state conditions of vessel pressures of 0psi, 5psi, 10psi and 15psi. The data generated was flow versus pump head outlet pressure at the different pressure conditions.
Figure 1 Process Setup (water at 23 Degrees C with 3/8 inch ID braided tubing and check valves with 0.5 psi cracking pressure)  
 
 
 
 
 
 
 
 
 
 
   
  Data: The data was generated using a simplex mode of operation. In this operating mode, there is a period of filling the pump and discharging the pump in each complete cycle as shown in Figure 4 (two complete cycles are shown). The period of relatively constant air pressure during a pump discharge is equivalent to the pump liquid outlet pressure. The liquid pressure at the vessel inlet is shown also in the figure. There is a slight elevation is pressure (about 0.2psi) when liquid flows into the vessel.
  Figure 2 Pump Outlet Pressure Versus Flow at
Different When Pumping Against Different Vessel
Pressures		 Figure 3 Flow Rate and Pump Pressure Changes
as Downstream Pressure Increases (with no flow
rate adjustments)
 
 
 
 


The effect of a changing downstream back pressure without adjusting the flow is shown in Figure 3. In a positive displacement pump, the flow is controlled by mechanical movement (such a movement of a piston or rotation of rotors in a peristaltic pump) and if downstream pressure increases, pump pressure increases. When using air pressure to transfer liquid from a pressurized vessel, a constant pressure is supplied and flow will drop if downstream back pressure increases. In Magma APS, the air is precisely metered into the pump at a certain setting that controls the liquid-out flow rate (NOTE: there is also a constant pressure mode possible). However, if the downstream back pressure increases, and the valve controlling the liquid flow out of the pump is not changed, the flow will drop and the pump outlet pressure will increase as demonstrated in Figure 3. The Magma APS external pressure warning feature could be utilized to prevent over-pressurization if downstream back pressure was to increase to a particular set-point. To maintain constant pressure, the liquid flow would need to decreased and to maintain constant flow, the liquid flow would need to be increased (and pressure would increase).

  Figure 4 Sample of Pressure Data Pumping Against 10psi vessel in Simplex Mode (two complete pump cycles shown and flow rate of 0.21 liter per minute and data Sampling rate one sample every 1.1 seconds)
     
   

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