Generally used for non-critical applications. When using standard weld pad gages, the tank must be relieved of pressure and drained to service the gage. Seal pots are a typical application. This type of gage is not used on process equipment (ex. Distillation tower in a refinery) because you cannot perform maintenance or replace a gage without shutting down the entire process. Isolable weld pad gages are available with needle-type isolation valves integral to the chamber.
Brochure: Weld Pad Liquid Level Gage Brochure
Drawings: Series 20 Weld Pad