Abstract: A fluid path opening/closing valve comprises a plate-like valve plug and a rack which is fixed to a piston of an emergency shut-down air cylinder. The rack meshes with a pinion which rotates by a reversible motor with a clutch. If a seismic detecting valve detects earthquake which has over predetermined seismic intensity and opens, compressed air is sent from an air tank via the opened seismic detecting valve to a switching cylinder which disconnects the clutch. At the same time, compressed air is sent from the air tank to the emergency shut-down air cylinder via a delay valve to lower the piston with the fluid-path opening/closing valve which closes the fluid path.

Abstract: In a swimming pool in which water is circulated by a pump, a schoolboy child is liable to be absorbed into a discharge port, which is dangerous. A sensor which has a load cell is provided at the back of a water-permeable cover in the discharge port. If a human body of the child is absorbed into the discharge port and contacted with the cover, the load cell is pressed by the water-permeable cover to transmit a signal to a control circuit in which it is determined whether or not pressure variation applied to the sensor is normal or abnormal. If abnormality is determined therein, an alarm is sounded to inform a watcher of the accident and the pump is stopped to release the child from the discharge port.