New Boiler

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.

new boiler
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.
lifting the boiler
The boiler  was lifted into the boat and the plumbing was done.


pi diagram

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, a 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.

Hot Well

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.
hot well


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 moving parts.
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 custom parts.

This injector in based on design in Model Engineer magazine.
injector pic
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 fully. 

injector testing
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 engine rotation. Because the force is directly proportional to the piston area, piston pumps can't pump high water volumes against high pressure. This is not a problem 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.
engine pump   enginepump
 Engine pump
handpump handpump2


You can find information about steam whistle design  here