Definitions for "Sight glass"
A glass tube, or a glass faced section of a process line, used for sighting liquid levels or taking manometer readings.
The gauge glass and its fittings for attachment.
A window into the A/C system. Installed in the liquid line or on the receiver drier, they are used to check refrigerant charge and flow. Newer systems using R-134a refrigerants rarely have a sight glass.
Keywords:  clear, fluid, window, line
A clear window in a fluid line.