Working principle of metering pump: the motor of metering pump rotates to drive the worm to rotate. The worm obtains the reciprocating motion of the connecting rod through the action of the worm gear mechanism and the eccentric wheel. The connecting rod pushes the piston to make the piston reciprocate in the metering pump working chamber (as shown in the figure). When the piston moves to the left, a vacuum is formed in the pump cavity, the suction valve is opened, the discharge valve is closed, and the liquid enters the pump cavity; when the piston moves to the right, the suction valve is closed, the discharge valve is opened, and the liquid is discharged from the discharge valve.