During operation, when steam connecting  pipe of the water level gauge is blocked,  because of the steam cannot enter the water level gauge, the original steam condensates, so that the top space of the water level gauge forms of partial vacuum, the water level indication will soon rise; When the water connecting pipe is blocked, the water in the water level gauge can't back into the drum, the steam condensation water in  water level gauge will gradually accumulate in the water level gauge, thus making the water level indication slowly rise. If the steam and water connecting pipe are blocked  at the same time, the water level gauge will lose water level indication function, and the water level stagnated. When the water connecting valve or water discharging valve of the water level gauge leaks, part of the water leaks, the water level indication is lower. If the steam connecting valve leaks and part of the steam leaks, the steam side pressure is reduced, the water level indication is higher.（lsh）