Three common types of pumps are constant pressure pumps, syringe type pumps and reciprocating piston pumps.

Figure 1.Constant pressure pump.

• Constant Pressure Pumps:As the name suggests, they provide constant flow rate in the column thanks to a constant pressure. They use the low pressure of a gas contained in a cylinder to create the desired high pressure of the mobile phase.

Figure 2.Syringe pump.

• Syringe Type Pumps:They use a motorized syringe to get a constant solvent delivery. Changing the voltage of the motor, different flow rates can be obtained.

Figure 3.Reciprocating piston pump.

• Reciprocating Piston Pumps:They consist of a hydraulic chamber were a reciprocating piston is placed. This way, solvent gets in the pump when the piston moves back and is pushed into the column when the piston moves forward.