When water or liquids in long pipes must be within a certain temperature range, A steam fitters "swing joint" may be installed in the line to allow pipe expansion or contraction without breaking the pipe.
Example: If pipe about 100 feet long has each end mounted solid in concrete a given pipe at certain temperature will have same pipe movement. We attach long lever flag to swing joint to detect this small movement shown as the long line in center part of vertical pipe along the bottom.
Now you are thinking, "if we have mechanical movement we can add micro- switches and alarms to this mechanical indicator and monitor this condition elsewhere." Right.
