Pumps pressurised coil

Figures. A diagrammatic representation of the pressurised coil pump.

Constant pressure pumps utilise pneumatics or hydraulics apply the pressure required to force the mobile phase through the column, either directly or indirectly. Two main designs of constant pressure pump exist the pressurised coil pump, and the pneumatic pressure intensifier type. The pressurised coil pump is now all but redundant, but as it represents the most simple means possible of pumping at high pressure through an HPLC column it is described briefly. 

The earliest form of constant pressure pump in hplc (the coil pump) used pressurised gas from a cylinder to drive mobile phase from a holding coil through the column. This type of pump was used in some of the older hplc instruments, but is now only of historical interest. If you want to know any more about it, there are details in most textbooks. 

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