The flowmeter of the present invention comprises at least two separate flow passages wherein one of the two flow passages include a shut-off valve with an actuator and the other of the two passage includes a flow rate sensor for measuring flow rate through that flow passage. In the mode of full capacity operation, both of the two flow passages stay fully open and the flow rate through the two flow passages is determined from the flow rate sensor measuring the flow through one of the two flow passages by multiplying by a factor such as two. In the mode of reduced capacity operation, the shut-off valve shuts off one of the two flow passages and the flow rate is directly determined from the flow rate sensor. The actuator actuating the shut-off valve may be controlled by the amplitude of the electric signals representing the flow rate wherein the valve is shut automatically when the amplitude of the flow signal is less than a preset threshold value and is opened automatically when the amplitude of the flow signal is greater than the threshold value, or it may be operated manually.