Please read what happened to the previous boiler!
The new boiler is Swedish B2 Ånga 25 kW vertical firetube boiler.
It has 53 liter water capasity and steam productiom capacity of 32
kg/h. The boiler diameter is b 525 mm, height 856 mm and weight 94 kg. I bought the boiler unfinished, so I had to paint,
insulate and panel it. The firebox had all the masondry work
done, but the grate was missing.
The new boiler panted with heat resistant paint.
The boiler was welded on 5 mm steel plate. Before the welding, the
plate was fitted to the supports on the boat. The boiler was
insulated with xx mm mineral wool and panelized with khaya panels from
the previous boiler. The panels were riveted with pop-rivets to the
steel bands welded around the boiler. The pop rivet rows were covered
with brass bands.
The boiler was lifted into the boat and the plumbing was done.
The plant is condensing with a surface condenser. The condenser
has been changed from a marine diesel heat exchanger to keel condenser. The boiler
is fed by engine pump,
piston pump, eccentric driven from crank shaft. The air
pump has been removed, because in single expansion engines the power
needed for the pump is aproximitely same as the extra power caused by
the vacuum at the exhaust. The condensed water is pushed by the
exhaust steam to the hot well.
B2 boiler is designed for fresh water use, where you can use the
exhaust steam improving the draught. With condensing plan and the
original boiler top it was impossiple to keep pressure with engine was
running. At the end of summer 2008 I installed the chimney blast to
improve the draught. In the chimney blast there is a small steam
nozzle, using fresh steam from the boiler, in the base of the
funnel. With the chimney blast it was possible to run the
engine normally, but it is noisy and wastes fuel and fresh water.
In the summer 2009 I made a new boiler top with more
room for the smoke flow from the fire tubes to funnel. In
addition to lower noise and better fuel and fresh water economy, heat
up time is ~15 minutes shorter with the new boiler top.
New Boiler top.
The purpose of the hot well is filter the lubrication oil out of
the condense water. The other purpose is to regulate the feed
water pump by pass with the floating valve. The oily water from
the condenser go to perforated tube and spreads evenly into
the oil absorbent. The absorbent is piece of foam from a old mattress.
In the bigger compartment of the hot well, there is a oil
absobant pillow floating, absobing the remaining oil. The pillow
is normally used fir keeping the pilge clean.
When the hot well is full the floating valve shuts off the bypass of
the engine pump and the water goes to the boiler.The bypass valve can also be a manual valve.
You can find more about the hot well design at Pegasus home pages.
Injector is a steam powered jet pump, which you can
pump the feed water to the boiler same or higher pressure than the
driving steam. Is has fairly simple structure and it doesn't have any
It has three main parts: steam nozzle (steam cone), combining tube
(mixing cone) an delivery tube (output cone).
Steam nozzle converts the pressure to velocity. Steam condenses in
combining tube and its volume is decreasing, building up vacuum. The
vacuum sucks the water from the container. The water gets high velocity
from steam and the divergent shape of delivery tube changes the speed
to pressure and the water pushes its way though a check valve to the
boiler. When starting the injector, steam escapes in the middle
of the combining tube to the first overflow and sucks the water. When
the water reach the combining tube, the steam starts to condense and
forming vacuum, which closes the check valve in the first overflow.
When the pressure in the delivery tube in not high enough, water run
through the second overflow. When the water pressure in the delivery
tube reaches the boiler pressure, check valve in the boiler feed
tube opens and the overflow stops.
More info about injectors and injector design you can find in
"Locomotive Injectors" published by TEE Publishing 1994 available at Chronos.
Another good injector book is Camden's
reprint of W.W.F. Pullen "Injectors,: Their Theory, Construction
& Working" 1893
My own injector design based on standard fittings and four
This injector in based on design in Model Engineer magazine.
Same in practice, before final polishing and installation.
These two injectors are under construction now and I will publish the
detailed drawing after I have tested them.
May 2004, the "Model Engineer" injector is under testing, not working
Testing the steam nozzle
Update!! Since I didn't get my
injector working, I went back to the theory. I just recently bought excellent
injector book: "The Model Injector" by Ted Crawford. It is published by
Australian Model Engineering and it is available from Camden. Reading
the book I realized that small size injectors are needing very accurate
manufacturing. This book very practical unlike the two books mentioned
above. It has chapter giving relative dimensions of the critical parts
of injector based on averages of published designs. I made a
injector calculator for the
injector cone dimensions, just fill in the feed rate. I
The ejector is also a jet pump and close relative of injector. I
use it as a bilge pump.
My ejector design uses standard 3/4" T-fitting is base of the ejector.
The combing/discharging cone is made of plastic
because of easier processing without lathe. I used a conical drill, normally used drilling different
size holes on sheet metal. The ejector can lift 30-40 cm (from bilge
bottom to ejector) at 4bar pressure.
Boiler Feed Pumps
The challenge of the feed water pumps is the boiler pressure. The feed
pump has to be able to pump against 10 bar boiler pressure. A
piston pump is good choice when pumping against high pressure. Its flow
direction is determined by the check valves, not the direction or
Because the force is directly proportional to the piston area, piston
can't pump high water volumes against high pressure. This is not a
in the engine pump, because the needed volumes are low, less than 80
l/h. But filling the boiler with the hand pump is real sports.
The cylinder diameter of the hand pump is 25 mm and engine
pump has 32 mm.
They utilize Parker-PDF B7 piston sealing. It is a
standard polyurethane sealing used in hydraulics. The piston has
been designed according the recommendations
of the piston sealing manufacturer. The engine pump is driven from
crank shaft with eccentric and the stroke length is 30mm. The hand pump
has longer stroke.
You can find information about steam whistle design here