Pumps:

A variety of pumps are used to maintain flow rate and pressure of the mobile phase. Also a degasser is needed to remove dissolved air and other gases from the solvent. A desirable feature of the delivery system is the capability of generating solvent gradient. A pump should be able to operate up to a pressure of 100 atm (1500 psi) though in some cases 400 atm (6000 psi) is desired. For many analytical columns, only moderate flow rates of 0.5 - 2 mL/min might be required. Therefore, for microbore columns, low flow rates of only a few microlitres/min might be sufficient. Also, a pump should have a small hold up volume.