Syringe-type pumps generally consist of a cylinder that holds the mobile phase which is expelled by a piston. The piston is advanced by a motor connected through worm gears, to provide smooth pulseless flow. Figure below shows the schematic of a typical syringe pump.
Syringe pumps have a number of advantages. Pressure capability is generally quite high (up to 78,000 psi) and maintenance is infrequent since there are no fluctuating check valves; gears are simple and strong.
The disadvantages of the system are the limited possibilities to form gradients and the limited reservoir capacity. Widely used in the early stages of HPLC, syringe pumps are now mostly used for SFC and microcolumn chromatography where the flow rates are 1 - 100 Ál/min. The 20 ml reservoir capacity is more than enough for the whole day operation.
Two of these pumps can be easily combined and driven through an electronic system which
provides mixed mobile phase and gradient-programming operation, or drive can be arranged
synchronously so that one pump can be refilled while the other is operating in order to
obtain continuous elution.