Patent ID: 6923916

Claim:
A method for controlling a pump for feeding a liquid for chromatography, including, first and second chambers, first and second plungers forming first and second volumes respectively together with the first and second chambers and being capable of reciprocating in the first and second chambers respectively in such a manner that the first and second volumes are variable in accordance with respective movements of the first and second plungers, a communication path connecting fluidly the first and second volumes to each other, an inlet path communicating fluidly with the first volume, from which inlet path the liquid to be fed is capable of being supplied into the first volume, and an outlet path communicating fluidly with the second volume, by which outlet path the liquid to be fed is capable of being discharged from the second volume, comprising the steps of: opening a drain valve in the outlet path to discharge a gas out of the outlet path through the drain valve so that the outlet path is filled with the liquid when the first plunger decreases the first volume, closing the drain valve when the second plunger decreases the second volume to discharge the fluid from the second volume to the outlet path for the chromatography, and controlling at least one of the movement of the first plunger for decreasing the first volume sufficiently for feeding the liquid from the first volume into the second volume and the movement of the second plunger for increasing the second volume in such a manner that a difference between a difference in absolute value between an increasing rate of the second volume increased by the second plunger and a decreasing rate of the volume of the first volume decreased by the first plunger and a desired flow rate of the liquid to be discharged from the second volume to the outlet path for the chromatography is kept within a predetermined range.