Trevithick Dredger Engine.. connecting the water pre-heater

by John

A few more hours in the workshop today.


The steam exhaust from the engine passes through a tube to the chimney.

Since this was the worlds first “strong steam” (high pressure) boiler, the water level in the boiler needs to be constantly replenished.

Trevithick thought that the water coming into the boiler could be preheated by the exhausted steam.  So he conceived a double tube, with the exhausted steam exiting through the inner tube, and the water being pumped through the outer tube….  A heat exchanger.  It was awkward to make using modern heat sources and silver solder.  I can only imagine how it was made 200 years ago, using castings and black-smithed iron panels.

The users noticed that the steam which was injected into the chimney improved the coal fire.


The cap screws are temporary, until I replace them with square nuts and stainless thread.

The hardest part of these connection pieces was keeping the flanges square to the 1/4″ copper tube while silver soldering them.    Any clever methods out there?