Liquid delivery pump and liquid chromatograph

A liquid delivery pump comprising:

• a primary plunger pump;
• a secondary plunger pump fluidly connected in series downstream of the primary plunger pump;
• and
• a pressure sensor that detects a system pressure that is a pressure of a mobile phase delivered from an outlet of the secondary plunger pump,
• wherein the liquid delivery pump is configured to alternately and continuously execute a primary discharge process in which the primary plunger pump performs discharge operation and a secondary discharge process in which the secondary plunger pump performs discharge operation,
• the liquid delivery pump further comprising:
• a liquid delivery control part configured to execute first constant pressure control in a first constant pressure control term and to execute second constant pressure control in a second constant pressure control term, wherein the first constant pressure control term is a term, which is in a liquid delivery cycle consisting of the primary discharge process and the secondary discharge process, in which the primary discharge process is executed, the second constant pressure control term is a part of a term in which the secondary discharge process is executed, and the second constant pressure control term is including a term that is continuous after the first constant pressure control term;
• and
• a target pressure setting part configured to set a target pressure for the first constant pressure control and the second constant pressure control with reference to the system pressure in a term other than the second constant pressure control term in the term in which the secondary discharge process is executed, wherein
• in the first constant pressure control, an operation amount of a combined flow rate, which is a flow rate obtained by subtracting a suction flow rate of the secondary plunger pump from a discharge flow rate of the primary plunger pump, is calculated using a first equation, and an operation speed of the primary plunger pump and/or the secondary plunger pump are/is adjusted so as to increase or decrease the combined flow rate by the calculated operation amount,
• in the second constant pressure control, an operation amount of a discharge flow rate of the secondary plunger pump is calculated using a second equation, and an operation speed of the secondary plunger pump is adjusted so as to increase or decrease a discharge flow rate of the secondary plunger pump by the calculated operation amount,
• the first equation includes at least a proportional term and an integral term of a pressure deviation that is a difference between the target pressure and the system pressure, and
• the second equation includes at least a proportional term of the pressure deviation, and degree of contribution of an integral term of the pressure deviation in the second equation is smaller than that in the first equation.