2008 - 2009.

John R. Bentley 2009.

Model Watertube Boiler

-  Tubing the Pressure Vessel  -

First row of tubes in the convection bank
Progress to March 17:
Second row - still dirty from brazing
Slightly curved tubes for the third row
Putting them in, prior to brazing
Pretty flux job, huh?
Fitting the final (fourth) row
Fourth row - ready for brazing
Done!  4 rows brazed - convection section completed
So far I am pleased with the joints
Checking out one of the deep-curved tubes for the furnace section
Now ... the D-tubes
Fitting the inner row
View showing a single tube from the outer row filling one of the gaps
The D-shaped furnace section is starting to take shape
The question here is how to keep them all flush during brazing...
An idea is hatched:
I will use two angle pieces made from soft copper to squeeze the C-shaped tubes into one plane.
These copper angle pieces were formed in the vise
The clamped angle pieces "sandwich" the straight sections of the tubes for alignment
End view
Clamps removed and the steam generator is still almost red hot after the brazing session
Temporarily putting short lengths of tubing into the gaps to act as spacers
The outer row of furnace-wall tubes (not yet brazed in)
- together the two rows will create a solid waterwall
Checking to see if it is flush
Citric Acid pickling after brazing the outer tubes
Outer furnace row of brazed joints
Viewing the fire
There is a viewing porthole in the back wall of the boiler enclosure...
This bifurcated tube surrounds that port, absorbing excessive heat near the glass.
Here's a view of the window cooling loop brazed in position
Looking from the firehole end
(note the window is located below centre - otherwise only the end of the burner would be visible)
Drum internals
End view of deflector baffle assembly
It's made from copper pipe and is silver brazed with a higher-temperature alloy
(to prevent a meltdown when the heads are brazed in)
Baffle unit's position in the upper drum
Looking upward, showing upper right deflector position, relative to uppermost tube ends
Making the steam outlet for the collector pipe unit
Some of the 54 steam entry holes positioned across the top of the collector pipe
The collector pipe assembly (holes on top not visible)
The collector pipe will be screwed into the phosphor bronze ferrule and silver brazed in position at the top of the boiler steam drum. The ferrule (bush) will comprise the main steam outlet of the boiler.
Collector pipe mounted in position between the upper deflectors
Steam entry hole locations along the top of the collector pipe are skipped directly below the safety valve openings to avoid being located in extreme low pressure areas when the valves open and the possibility of water being carried over into the outbound steam.
Bronze ferrules (bushes)
Sawing up some more phosphor bronze to make threaded bushes for the smaller fittings
Making the smaller piece round
Finished threaded bush for the main steam outlet
It is extra tall so it will be be flush with the roof of the boiler casing (allowing for the thickness of the insulation)
I will position the tops of the two threaded bushes for the safety valves below the roof of the boiler casing (at the level of the drum the drum). This will allow some extra hidden length for the valves. With only the upper portion of the safety valves visible, they can be made to appear closer to scale in appearance yet function properly without hindrance due to extra space within.
A fistful of copper
I'll be glad when the drum heads are attached and the vessel has been pressure tested.  I went out for more citric acid, silver brazing alloy, propane and steel wool  today -  so I should be ready!
The phosphor bronze ferrules, brazed into the top drum
(blanking plugs screwed in)

That's all the tubes brazed in place...the drum heads are next.