METHOD FOR DETECTING FLUID FLOW

PROBLEM TO BE SOLVED: To provide a method for detecting the flowing state of fluid in an ink jet printer. SOLUTION: In the method for detecting the flow of fluid, a low speed air flow type catcher 18 is provided in order to form a bubble flow in a catcher vacuum port and a catcher return line 25. Pressure fluctuation of returning fluid is monitored in the catcher return line to an ink tank 30 having tank vacuum pressure. The tank vacuum pressure is lowered automatically to a predetermined level higher than the bubble flow forming level. Subsequently, the vacuum pressure of tank is lowered increasingly while monitoring the pressure fluctuation. When the pressure fluctuation 15 reduced lower than a predetermined level due to formation of a bubble flow, the vacuum pressure of tank is sustained at a constant level. The vacuum pressure of tank is increased by a predetermined level and the increased level is sustained as the operating point for the bubble flow of a printer.