A Bridle is a special piping arrangement done by the piping designer to hold the Level Instruments for a Vessel or Tank.
Level instruments such as: Level Glass (or Gage), Level Transmitter, Level Controller and Level Alarm. See example of an Instrument Bridle below.
You should note that there are three parts here. In the middle there is a “Stand Pipe” or “Stilling Well”. This is just a pipe to connect all the instruments to instead of connecting them directly to the vessel (not shown is the connection from the “Stand Pipe” to the Vessel). On the left is a Level Controller (LC). On the right is a Level Glass (LG). The LG is there to, a) give the operator a quick local visual indication of the liquid in the Tank or Vessel and, b) to give the operator the ability to have a visual indication of the liquid when setting the LC controls. The valves are for shut-off of the individual item for removal and repair without shutting down the whole plant.
This text is an extract from questions gathered from numerous queries of anonymous people in the Piping Engineering and Design profession. The answers or discussion of the topics were provided by James O. Pennock. Images obtained from www.coastalflange.com