A piezoelectric DOD printing system including a piezoelectric-based print engine, a micro pump, an ink line, a vacuum sensor, and control circuitry. The micro pump delivers ink from a cartridge reservoir to the print engine. The ink line fluidly connects an outlet of the micro pump with an inlet of the print engine. The vacuum sensor is fluidly connected to the ink line. The control circuitry is electrically coupled to the vacuum sensor and programmed to control operation of the print engine and the micro pump. The control circuitry activates and deactivates the micro pump based upon information from the vacuum sensor.