The De Winton Boiler
(by Colin Binnie)

A DeWinton boiler is small and if kept simple has a single but rather short vertical centre flue up which the hot gases from the burner pass. Unfortunately they do this with great facility without giving up much heat to the surrounding water.  The first problem is in the flue itself. Athough the moving gas column is very hot, the layer of gas adjacent to the flue walls soon gives up its heat   and sticks to the walls while the core of the gas column carries its heat out of the chimney.  To combat this I have copper rods about 2,5mm dia passing through the flue every 12mm..  Each is set at right angles to the previous one.  The real function is to promote turbulence in the gas flow and cause some of the hot central gases to impinge on the walls. They also conduct heat directly into the water.  At this spacing and diameter they do not unduly constrict the gas flow through the flue.   They are shown in figs 1 and 2.

   A further measure, intended to promote a spiral and turbulent gas flow is the provision of fins on the bottom of the flue tube.   The end of the flue tube has saw cuts in six positions and after silver soldering into the base of the boiler the projecting tabs are twisted through a right angle and pushed back against the base of the boiler.  Fig 3 should make this clear.

The next problem is in the firebox. The boiler base plate is the major heating surface but as soon as the engine starts working the induced draught pulls the flames inward and directly up the flue.  Apart from being inefficient in terms of heat transfer the flame length is severely curtailed and unburnt gas goes to waste.  So just above the burner I have a deflector plate which just like the brick arch in a full size boiler increases the flame path and allows combustion to be completed before it enters the flue. It also ensures that the hot gases do impinge on the base of the boiler. See figs 1 and 2.  A further benefit is that any oil drips falling back down the vertical flue do not land on the burner but vapourise and burn on the deflector. Steam is taken from the top of the boiler via a 5mm o/dia tube  which passes through the baseplate before making a loop around the top corner of the firebox. It reduces to 3mm o/dia as it leaves the firebox.

The thinking here is that since the internal cross sectional area of the 5mm tube is about two and a half times that of a 3mm tube the steam would spend  two and a half times as long soaking up heat as it passed through the firebox. The burner is a simple gas ring constructed as in fig.4. The upper half with its holes spigots into a hole in the base. The incoming gas tube butts up against the spigot  and is cut away on its lower half so that incoming gas spreads evenly in the burner. This is how my DeWinton boilers are constructed.   They are not perfect. They are slow to fire up.  When the boiler and hence the gas column is cold they cannot be forced.  Once the boiler is hot they do their job very well .

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