| 摘要 |
PROBLEM TO BE SOLVED: To provide a check valve having a valve element displacement detecting function capable of effectively detecting a small amount of counterflow caused when a small foreign object is bitten, which is difficult to detect by a conventional structure. SOLUTION: The check valve includes a valve stem in a valve case. The valve stem slides along the direction of passing of water toward a secondary side of the valve element urged in a valve-closing direction by a spring pressure. The check valve has a measurement target portion arranged integrally with a secondary side of the valve stem and having an electromagnetic responsiveness, a sensor head which generates a high frequency magnetic field by passing a high-frequency current through a coil and is located at a position where a coil impedance changes depending on a distance between the measurement target portion and the sensor head, and a displacement calculating portion for calculating the displacement of the valve element based on oscillation output from the sensor head. A sensor casing made of a non-magnetic material is connected to a secondary side of the valve case so that they are in a shape of a straight tube. The sensor head is arranged on a secondary side of the sensor casing via a waterproof wall and the measurement target portion is arranged on the secondary side of the valve stem so as to extend into the sensor casing. COPYRIGHT: (C)2008,JPO&INPIT
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