Liquid feeding pump and liquid feeding method

A liquid feeding pump comprising:

• a first plunger pump including a first plunger;
• a second plunger pump connected to the first plunger pump in series, the second plunger pump including a second plunger;
• a pressure sensor disposed downstream of the second plunger pump;
• a control section that controls driving of the first plunger and driving of the second plunger;
• and
• a memory section that stores a compression rate parameter for calculating an amount of compression of a solvent by the first plunger,
• wherein the control section is configured to:
• calculate a first amount of compression of the solvent by the first plunger in one driving cycle based on the compression rate parameter and control the first plunger to compress the solvent by the first amount of compression in the one driving cycle;
• when a change amount of the compression rate parameter changed in accordance with a pressure value measured by the pressure sensor is smaller than a threshold in the one driving cycle, change the compression rate parameter in accordance with the pressure value and calculate a second amount of compression of the solvent by the first plunger in a subsequent driving cycle, which is subsequent to the one driving cycle, based on the compression rate parameter after being changed by the controller in accordance with the pressure value;
• and
• when the change amount of the compression rate parameter is greater than the threshold, calculate a third amount of compression of the solvent by the first plunger in the subsequent driving cycle, based on the compression rate parameter.