"all sealed electronic flag type" if you're referring to a magnetic flag type, those are not permitted in-place of the gauge glass per boiler code. Direct reading gage glass is required per boiler code (ASME Sec.I PG-60). However by keeping the direct reading gage glass, you can add a magnetic...
That diagram is the source of ambiguity on this subject. I've seen end users require an S-stamp level gauge, and USA Mfg companies can provide the LG as such (optional). However, the common industry practice is that the LG is built to comply with ASME code requirements (PG-60), without a stamp.
Direct reading armored sight glass (both reflex and transparent) are made using tempered borosilicate glass in standard form. Shields are used to protect the glass for applications where the glass is not compatible with the vapor or liquid phase. For example a fired boiler drum at 500 PSI WSP...
