Liquid delivery device, liquid chromatograph, and method for operation of liquid delivery device

1. An improved liquid delivery device having a plurality of cylinders, each with a reciprocating plunger, a motor to drive said plunger, a control unit to control operation of said motor, a discharge pressure detector to measure the discharge pressure of the liquid being discharged from said cylinders, and a cylinder pressure detector to measure the pressure of said liquid flowing in said cylinders,

wherein said improvement is characterized in that said control unit establishes the judgment point before the pressure measured by said cylinder pressure detector agrees with the pressure measured by said discharge pressure detector and controls the speed of rotation of said motor on the basis of the discharge pressure measured by said discharge pressure detector and the pressure measured by said cylinder pressure detector.

2. A liquid chromatograph equipped with the liquid delivery device defined in claim 1 , a column, and a detector.

3. An improved liquid delivery device having a plurality of cylinders, each with a reciprocating plunger, a motor to drive said plunger, a control unit to control operation of said motor, a supply flow channel to supply a liquid from the supply source to said cylinder that functions as a supplier, an inlet valve means attached to said supply channel, an intermediate flow channel to lead said liquid, which has been pressurized in multiple stages including cylinders at said supply side, to said cylinder in the final stage, an outlet check valve means attached to said intermediate flow channel, a discharge pressure detector to measure the discharge pressure of said liquid being discharged from said cylinder in the final stage, and a cylinder pressure detector to measure the pressure of said liquid flowing in said cylinders excluding said cylinder in the final stage,

wherein said improvement is characterized in that said control unit establishes the judgment point before the pressure measured by the said cylinder pressure detector agrees with the pressure measured by said discharge pressure detector and controls the speed of rotation of said motor on the basis of the discharge pressure measured by said discharge pressure detector and the pressure measured by said cylinder pressure detector.

4. An improved liquid delivery device having a first cylinder supplied with an eluent, a second cylinder which is connected in series with said first cylinder and discharges said liquid which has been pressurized repeatedly, a motor to drive a first plunger and a second plunger which reciprocate in said first cylinder and said second cylinder, respectively, a control unit to control the motion of said motor, a discharge pressure detector to measure the discharge pressure of said liquid discharged from said second cylinder, and a cylinder pressure detector to measure the pressure of said liquid flowing in said first cylinder, wherein said improvement is characterized in that said control unit has a function to read the discharge pressure of said discharge pressure detector, a function to calculate the judgment pressure, which is lower than the discharge pressure of said second cylinder, on the basis of the value of width in which the pressure is set up, a function to calculate the rate of change in pressure (K) of said first cylinder on the basis of the change in pressure in said cylinder pressure detector, a function to calculate the point of completion of compression at the high-speed rotation of said motor on the basis of said rate of change in pressure (K) and said value of width in which the pressure is set up, a function to judge that the pressure of first cylinder which said cylinder pressure detector detects has reached the judgment pressure, and a function to make said motor continue high-speed rotation until said point of completion of compression when the pressure of said first cylinder has reached the judgment pressure and shifts the high-speed rotation to low-speed rotation after the pressure of said first cylinder has passed said point of completion of compression.