The liquid feeding device includes a discharge speed calculation part configured to calculate a discharge speed v of the plunger pump so that a converted value L.sub.ATM under an atmospheric pressure of a flow rate L.sub.PRE of the mobile phase discharged to the discharge channel from the pump part becomes a set flow rate L.sub.SET using a volume V of the mobile phase in the pump chamber of the closing pump immediately before the precompression process is started, a volume ΔV reduced due to the precompression process of the mobile phase in the pump chamber of the closing pump, and a feeding pressure P; and a discharge operation controller configured to control a discharge speed of the plunger pump to a discharge speed v calculated by the discharge speed calculation part.

A closed-loop hydraulic circuit includes a piston chamber housing a piston rod and a ram piston coupled to an end of the piston rod, and a pump in fluid communication with the piston chamber at first and second hydraulic ports. Pumping a hydraulic fluid to the first hydraulic port causes a forward stroke of the ram piston and the piston rod, and pumping the hydraulic fluid to the second hydraulic port causes a return stroke of the ram piston and the piston rod within the piston chamber. An accumulator is in fluid communication with the pump and the piston chamber, and a 3-2 valve is actuatable between a first position, where pressurized hydraulic fluid is conveyed from the accumulator to the pump during the forward stroke, and a second position, where excess hydraulic fluid is conveyed from the first hydraulic port to the accumulator during the return stroke.

A solvent supply system for supplying a composite includes a first supply path with a first pump unit, the first supply path being adapted for supplying a first solvent to a mixing unit, the first pump unit operating periodically, and a second supply path with a second pump unit, the second supply path being adapted for supplying a second solvent to the mixing unit, the second pump unit operating periodically. The mixing unit is adapted for mixing the first and the second solvent and for supplying a composite solvent. The solvent supply system further includes a control unit adapted for controlling operation of the first and the second pump unit.

Provided is a tube pump including: a housing unit that has an inner peripheral surface, which is formed in an arc shape around an axis, along which a tube with flexibility is disposed, and that is opened toward one end side along the axis; a pair of roller units that are accommodated in the housing unit and rotate about the axis in a state in which the tube is blocked; a pair of drive units that cause each of the pair of roller units to rotate about the axis in the same direction; and a cover member that is disposed in the housing unit such that the cover member covers the pair of roller units and provides an annular opening region into which the tube is able to be inserted toward the inner peripheral surface.

A solvent supply system for supplying a composite solvent is described. The solvent supply system comprises a first supply flow path with a first pump unit, the first supply flow path being adapted for supplying a flow of a first solvent to a mixing unit, the first pump unit operating periodically, and a second supply flow path with a second pump unit, the second supply flow path being adapted for supplying a flow of a second solvent to the mixing unit, the second pump unit operating periodically. The mixing unit is adapted for mixing the first and the second solvent and for supplying a composite solvent. The solvent supply system further comprises a control unit adapted for controlling operation of the first and the second pump unit, the control unit being adapted to prevent at least one of a predefined phase relation and a predefined frequency relation between the first pump unit and the second pump unit.

A positive displacement pump for pumping a fluid mastic comprises a plurality of cylinders each having a piston arranged for reciprocal motion within the cylinder. Movement of the piston in a first direction draws the fluid into the cylinder and movement in a second, opposite direction pumps the fluid out of the cylinder. A variable speed electric motor is drivingly coupled to a cam arrangement providing a reciprocating drive to the pistons. The cam arrangement comprises cams shaped and arranged to drive each piston in the first direction over less than half of a rotational cycle and to drive each piston in the second direction over the remainder of the rotational cycle. The cams are arranged to drive the pistons out of phase with one another.

A tube pump system is provided, which includes a pair of roller units which are rotated around the axis line from a contact position to a separate position in a state where the pair of roller units compress the tube, a pair of drive units which rotate the pair of roller units respectively, and a control unit which controls each of the pair of drive units, wherein the control unit controls each of the pair of drive units such that, when one of the pair of roller units passes the separate position, an angular velocity of the other of the pair of roller units toward the separate position is gradually decreased.

A positive displacement pump for pumping a fluid mastic comprises a plurality of cylinders each having a piston arranged for reciprocal motion within the cylinder. Movement of the piston in a first direction draws the fluid into the cylinder and movement in a second, opposite direction pumps the fluid out of the cylinder. A variable speed electric motor is drivingly coupled to a cam arrangement providing a reciprocating drive to the pistons. The cam arrangement comprises cams shaped and arranged to drive each piston in the first direction over less than half of a rotational cycle and to drive each piston in the second direction over the remainder of the rotational cycle. The cams are arranged to drive the pistons out of phase with one another.

A control device of a piston pump unit comprising at least two piston-cylinder units that operate in a phase-shifted manner for the purpose of liquid chromatography and to a piston pump unit is described. The control device corrects fluctuations of the system pressure while switching from one piston cylinder unit to the respective other piston cylinder unit. The fluctuations can occur as a result of the cooling of the liquid medium that is heated in an adiabatic manner during a pre-compression phase in the working piston. The control unit controls the piston speed of at least one piston-cylinder unit during the transition phase depending on at least one characteristic, which is ascertained from chronologically previously detected pressure values, such that variations of the system pressure as a result of the cooling of the adiabatically heated medium are at least partially compensated for.

A pumping system includes at least three electrically driven pumping units. Each pumping unit includes a linear actuator driven by at least one electric motor and driving a shaft. Pistons on each end of the shaft move within fixed cylinders to draw fluid from an inlet and expel the fluid to an outlet. Each pumping unit draws fluid at one end while expelling an equal quantity of fluid at the opposite end. The shaft velocity is controlled such that a total flow of the pumping system is constant, eliminating flow ripple.