All boilers having a fixed water level (steam and water interface) shall have at least one gage glass (a transparent device that permits visual determination of the water level). Boilers not having a fixed water level, such as forced-flow steam generators and high-temperature water boilers of the forced circulation type, are not required to have a gage glass. The lowest visible water level in a gage glass shall be at least 2 in. (50 mm) above the lowest permissible water level, as determined by the boiler Manufacturer. Electrode - type electric boilers are required to have only one gage glass, regardless of MAWP. Gage glasses having multiple tubular sections shall have a minimum of 1 in. (25 mm) overlap of the sections in which the water level may be visible. Segmented gage glasses, such as ported or end-connected strip gages, shall be equipped to provide obvious visual discrimination between water and vapor in the individual sections.
Boilers having a maximum allowable working pressure exceeding 400 psi (3 MPa) shall have two gage lasses. Instead of one of the two required gage glasses, two independent remote water level indicators (two discrete systems that continuously measure, transmit, and display water level) may be provided.
Boilers having a maximum allowable working pressure exceeding 400 psi (3 MPa) shall have two gage lasses. Instead of one of the two required gage glasses, two independent remote water level indicators (two discrete systems that continuously measure, transmit, and display water level) may be provided.
ASME Section I 2004 Edition.
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