A back view of the tiny partially completed boiler
I felt, that with so many unfinished projects in my workshop far from completion, it would be nice to have a good general purpose miniature boiler to run a few steam engines for demonstration and experiment. I have three finished engines on hand which are not connected to steam plants and it seems a shame not to be able to run them for guests - except on noisy compressed air. The charm of a steam engine is totally lost when visitors are denied the pleasant smell of warm oil, feeling the heat and hearing the sound of the exhaust. This boiler job provides a break from my Naphtha Launch Engine project which really has a lot of work yet to be done.
Early mockups to give an idea of the general arrangement
A later shot showing further work on the burner
This is not quite so serious as it might first appear :-)
The fabricated bottom skid of the boiler awaiting cutouts for the mud drum
Please note:
Pressure boilers which are improperly designed, constructed or operated can be dangerous regardless of their size. As I have stated elswhere, this is not a suggestion about how someone else should build a boiler but simply a description of how I made this particular example.
Of course the past year was the second year of the pandemic so let's hope that the virus will burn itself out in 2022 and we can all start having fun again.
Here on our island 2020 was our hottest summer on record and wasn't great for working on the boiler or this website. Due to that I chose to spend more time with family and renewing old friendships (you might say my boiler and these web pages have been on the back burner recently). That carried on throughout 2021 and consequently the following pages have not been fully edited, just as the model is also not yet completed. There could be some inaccurate references, and typographical, gramatical or spelling errors. I hope to get back to my workshop and to more editing soon. - John
(This is not a large model - the boiler only stands as tall as my hand)
(obviously the burner components were held together with clamps for these photos)
(including temporary paint)
Test fitting a power supply module into one of the three electrical boxes on the burner front
The burner is intended to run without any electrical (or electronic) assistance. A tiny steam turbine blower will provide the necessary draft through the boiler as well as supplying secondary air for the methanol burner. However during starting, a battery powered electric motor will do that work until enough steam is raised for the turbine. As the motor, turbine and blower fan all share a common shaft, the motor will act as a micro power generator when the turbine is operating. I thought it would be nice to use an electronic voltage regulator to operate LED panel lights thereby indicating when it is safe to disconnect the battery supply from the motor after steaming up.
The pressure vessel in the final construction stages
I have embarked on a miniature D-boiler, modelled loosely after the large Cleaver-Brooks packaged industrial watertube boilers. This model will represent a typical CB D-series boiler circa mid-1970's. As a model it has much smaller drums than my original plan for a similar size Babcock boiler and hence materials for it are less problem to obtain.
D-type boiler is a term used particularly in North America which simply denotes a pressure vessel configuration which resembles a capital letter "D" when viewed from the end. Two small drums are located on the vertical line of the D - one at the top (the steam drum) and one on the bottom (mud drum).
In operation: the fire is projected longitudinally through the open space of the D, which is enclosed by walls of water-filled tubes. These tubes receive heat by radiation from the flame. When the hot combustion gases reach the back end of the boiler, they are turned around 180 degrees and come forward between a bank of vertical water tubes (convection bank) which extract heat by contact with the gases as they pass toward a large flue gas outlet at the front of the side wall leading to the smokestack. This convection bank is represented by the thick vertical line on the left side of the capital letter "D". Typically as much as 70% of the heat is transferred to the water in the open section of a D boiler and the remaining 30% of the heat transfer takes place on the return pass through the convection bank. It is a popular type of boiler both on land and formerly in oil-fired warships.
Of course my boiler will require fittings, but they will be larger and
different from those above out of practical and safety considerations.
My plan is to use this model as a small shop boiler to run a few of my loose engines and to test any new ones that I may make. A watertube boiler is not always the best for the shop as it requires paying close attention to water and firing levels much more diligently than a pot boiler. However a watertube type raises steam very quickly and is faster to shut down - well suited to the requirements of quick testing in the workshop.
Note:
I am adding comments and pictures as I work along in this project. Some of the text here (and in pages to come) may appear to suggest that the
"present" covers a very long span of time which started some weeks, months or even years
ago. Please remember also that in many cases the "future" as referred to in these pages has already come and gone!
End flanges partially formed
Two ends finished and silver brazed
Beginning the assembly of the skid
Lots of clean-up and silver
brazing yet to do
A dull pencil is a sign that lots of
work has been going on!
(those are not "rusty spots" but some sporadic copper plating that happened in the pickle solution)
Convection-section floor
with the supporting gusset piece awaiting brazing
The mud drum shell being tested in its eventual position
Cooling off - upside down after silver
brazing
Back into the acid!
Painted in red oxide...the mud drum cradle is
visible here
(the shed roof piece on the right actually overhangs the wall - that's a pencil line on the roof, not the top edge of the right wall)
Checking that the four corners are in one plane on a granite surface block
Now it's time to join walls and roof (along the white seam)
Easy-flo 45 has flashed into the joint
beautifully -
There is Commercial Bronze - no good, as it
contains too much zinc, there are machining bronzes which contain lead, but Phosphor
Bronze A, B or C are almost "pure bronze" - copper and tin. They will not
disintegrate in a model boiler like many of the brassy bronzes.
or