Liquid delivery devide and liquid chromatography device

A liquid delivery device comprising:

• a first cylinder and a second cylinder which are connected to each other via a flow passage conduit pipe;
• a first plunger and a second plunger which are provided in inner portions of said first cylinder and the second cylinder, and reciprocate within the respective cylinders;
• an inlet-side check valve which is provided in an inlet side flow passage of said first cylinder;
• an outlet-side check valve which is provided in said flow passage conduit pipe of the outlet side flow passage from said first cylinder;
• a cylinder internal pressure detector which measures a pressure within said first cylinder;
• a discharge side flow passage internal pressure detector which measures a pressure within the discharge side flow passage from said second cylinder;
• a motor which drives said first plunger and the second plunger in such a manner as to carry out reciprocating motions having approximately reverse phases;
• a control unit which controls a rotation of said motor;
• and
• an eluent being sucked into said first cylinder from said inlet side flow passage, and the eluent within said second cylinder is discharged from the discharge side flow passage, if a moving direction of said first plunger is turned to a direction of enlarging a volumetric capacity within said first cylinder from a direction of reducing it, said outlet-side check valve is closed, and said inlet-side check valve is released,
• wherein said control unit is structured such that when the moving direction of said first plunger is turned to the direction of reducing the volumetric capacity within said first cylinder from the direction of enlarging it, said inlet-side check valve is closed, and the compression of the eluent within said first cylinder is started,
• said control unit increases a rotational speed of said motor,
• said control unit measures a change amount of the pressure within said first cylinder until a predetermined first elapsed time has passed before the pressure within said first cylinder reaches the pressure within said discharge side flow passage, from the compression starting time of the eluent within said first cylinder, by means of said cylinder internal pressure detector,
• said control unit calculates a time change rate of the pressure within said first cylinder on the basis of said first elapsed time and said measured change amount of the pressure within the first cylinder,
• said control unit estimates a second elapsed time until the pressure within said first cylinder comes to the same pressure as that within said discharge side flow passage after starting the compression of the eluent within said first cylinder, on the basis of said time change rate of the pressure, and
• said control unit determines that the pressure within said first cylinder comes to the same pressure as that within said discharge side flow passage in the case that the elapsed time after starting the compression of the eluent within said first cylinder reaches said estimated second elapsed time, thereby executing such a process as to reduce the rotational speed of said motor to a speed before being increased,
• wherein when the rotational speed of said motor is reduced on the basis of the process, said outlet-side check valve is opened, the compression of the eluent within said first cylinder is finished, the eluent within said first cylinder is delivered to said second cylinder, and the eluent overflowing from said second cylinder is discharged out of said discharge side flow passage.