The phenomenon, that the flow rate of a loop with a cross pipe switches nonperiodically between a high level and a low level under certain flow conditions was experimentally investigated by using air flow test equipment (Re≒2×105). The influence of the branching discharge ratio and structural factors (e.g. the offset angle and length of laterals of the cross pipe) on the phenomenon was found. A switching occurs in the case for the offset angle of about 8 to 20°, and it is restricted within a certain range of the branching discharge ratio. The discharge ratio of the center branching pipe to the main pipe at the peak value of the branching loss coefficient increases as the offset angle increases. In the case for the flow rate of the lateral exceeding about 1.7 times as that of the opposing lateral, switching does not occur.
