Mobile phase composition is produced by mixing the outputs of pump A and pump B. The solvent selection valve allows the pump A output to originate from either channel A1 or channel A2. The pump B output may originate from either channel B1 or channel B2.
The primary flow produced by the two pumping units is proportioned in an electromagnetic proportional valve (EMPV). The remaining column flow is measured in a mass flow sensitive flow sensor. The measured flow is compared with the user-entered column flow setpoint.
The flow sensor controls the EMPV current, causing the EMPV to correctly proportion the column flow. The primary flow in excess of the required column flow volume is directed to the waste.
Solvent degassing is not done directly in the pump. A 4-channel, low volume micro vacuum degasser, available as a separate module, provides degassed solvents to the pump channel inputs. Solvent degassing is required for best flow stability and detector stability, especially at the low flow rates required to run nano LC applications.
The flow range of the nano pump is between 0.1 μl/min and 1 μl/min.