| 摘要 |
PROBLEM TO BE SOLVED: To miniaturize a gas meter, to simplify a structure of a master/slave meter selector valve, to improve reliability, to widen rangeability in use of an estimation type flow meter, and to reduce a pressure loss and a cost in installation of a shut-off valve essential to a safety function. SOLUTION: In a low flow rate time, a flapper valve 7 is closed. Gas fed from an inlet 2 passes between a valve element 4 and a valve seat 5 of the shut-off valve 3 and passes through an ultrasonic flow meter 15 in a bypass flow passage 13 via an inlet port 12 from a communication passage 9 so as to flow to an outlet port 14. When a valve pressure difference of the flapper valve 7 is increased according to increase of a flow rate, the flapper valve 7 is opened, and the gas merges with the flow in the bypass flow passage 13 and passes through an ultrasonic main flow meter 18 so as to flow outward from an outlet 19. A flow rate at this time is measured by means of the main flow meter 18.
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