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At present, the plunger pump is the main infusion unit of liquid chromatography, especially the double plunger reciprocating pump. It has a well-designed eccentric cam, which is driven by synchronous motor or variable speed DC motor. The eccentric cam drives two pistons to move back and forth. At the same time, another piston corresponding to the long radius end of the eccentric cam is pushed in to open the upper one-way valve and send the mobile phase to the chromatographic column. The utility model has the advantages of convenient operation, stable flow rate, small pressure fluctuation and low failure rate.