Apparatus for metering and discharging a liquid

A liquid dispensing apparatus comprising:

• a syringe containing liquid;
• an air supply coupled to the syringe for supplying air under a positive pressure to the syringe;
• a dispensing solenoid valve disposed between the syringe and the air supply;
• a first pipe line disposed between the syringe and the dispensing solenoid valve;
• a second pipe line disposed between the dispensing solenoid valve and the air supply;
• a first pressure sensor for measuring the internal pressure in the first pipe line;
• a second pressure sensor for measuring the internal pressure in the second pipe line;
• an accumulator coupled to the second pipe line;
• a controller means for outputting a shifting output signal to the dispensing solenoid valve and for controlling an output time of the shifting output signal in accordance with a variation of an integral value of pressure measured by the first pressure sensor integrated during a preset output time of the shifting output signal after communicating with the first and second pipe lines;
• a suction solenoid valve coupled to the dispensing solenoid valve by a third pipe line;
• an air suction source coupled to the suction solenoid valve by a fourth pipe line;
• a vent solenoid valve coupled to the third pipe line;
• and
• an accumulator coupled to the fourth pipe line, each of the solenoid valves being coupled to the controller.