Communication occurs between a server and a terminal. A cylindrical valve conduit having a hollow structure, a yoke and a sensor conduit are connected in tandem. The backboard includes a frame and a light-shield plate. By employing the current detection values, the high voltage control unit can identify and provide notification of a location where the leakage current is increased and the insulation is deteriorated, and can request an operator to perform maintenance for the pertinent location. The vortex generated inside the chamber body will scour the surface of the metal diaphragm continuously so as to cool the heat and remove the air bubble.