No 21 Backhead Detail
NPC No 21 was the first engine built with a marine boiler.
Furthermore, it was a water tube boiler. So the big question was, what
kinds of devices were installed on its backhead. No complete drawing of
this area of No 21 has surfaced to this point.
The following is two photos and a drawing of the backhead of a
Yarrow Boiler installed in the New Zealand Steamer Waimarie in 1889 by the
Yarrow Company in London.
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While No 21's boiler is definitely not a Yarrow Boiler, it
shares the characteristic that an upper steam tube contains a combination
of water and steam. both are water tube boilers. |
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This photo of the engine, after being salvaged from the river shows the
upper steam tube. Both the water tubes and the tri-cocks (or
bi-cocks) are located on the upper steam chamber as that is where the
water level needs to be monitored and controlled. |
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In this photo, the dual water tubes are even more
apparent. The valves for two of the three tri-cocks are to the left
of and between the water tubes. Note that a tube from the tri-cocks
routes the water down past the back of the boiler toward the bottom of the
engine where it can be safely discharged. |
The boiler for No 21 also contains an upper steam tube mounted above the
boiler as the following two drawings show.
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Four vertical tubes connect the boiler to the upper steam
tube in this drawing. Note that the steam tube is half filled with
water, the other half with steam.
Click drawing for a larger image. |
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The left drawing shows the back side of the boiler.
The hand holes appear in this drawing. The curved tubes going up each side of the boiler route
steam from the steam chamber to the cylinders under the cab. A T connector is at the level of the top of the
cab. As can be seen from the previous drawing, they connect and then
the line runs laterally the length of the steam chamber.
Click drawing for a larger image. |
In order to gain resolution and detail, I blew up key sections of these two
drawings.
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Not a lot is revealed in this photo other than a blown up
version of the pipes coming down from the steam chamber routing steam to
the cylinders. What is not shown in the drawing is the two hydrostatic lubricators
that were mounted, one each on each of the pipes. The lubricators
show on a later photo. The hydrostatic lubricators provide steam oil
to the cylinders in order to provide
lubrication to the cylinders.
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This drawing reveals a number of key backhead details.
- The piping at the top of the drawing is where the vertical pipes to
the cylinders join forming a tube exiting out of the drawing to the right into the steam tube.
This is the dry tube that picks up steam from the steam chamber.
- The handle hanging down from that area
is the throttle, controlling the quantity of steam to the cylinders.
- A water tube is visible immediately below the cylinder pipes in the
top right corner of the drawing.
- Further down is a lever. We've concluded that it controls the
air intake into the boiler by controlling the size of the openings to
the right of the lever. These openings are air holes that
admit air to the combustion chamber. Note that this device does
not show in any of the photos showing backhead detail. It was
mounted to the large hole in the bottom of the backhead in the
previous photo.
- To the left of the air control lever is a floor mounted Johnson bar.
- Not shown is a set of tri-cocks. If they existed, they would
have been mounted to the steam chamber to provide a separate way of
measuring water level than the water tube.
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These photos show the rear portion of the boiler while under construction.
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This photo shows the back portion of the boiler during the
inner jacket part of construction. There were 40 water tubes in this
boiler. The large round opening at the bottom of the boiler is the
combustion chamber. Two rings are shown on the right side of this
photo.
The closer outer ring is the actual backhead. The holes are the
hand access holes to the tubes. The inner ring contains the ends of
the tubes. Light shows through the holes in the outer rings because
the inner jacket has not yet been slid into the outer jacket.
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This photo shows the boiler and steam tube after
installation of the outer jacket. Note the vertical pipes connecting
the steam tube and boiler. Both water and steam flowed through these
tubes. We are looking at the actual backhead.
Notes in the Harlan book indicate there were hand hole openings in the
backhead for access to the tubes. You are looking at the hand
holes. They are likely to be oval in shape to allow the metal plates
covering these openings to be slid inside the backhead. The small
dark spots between the hand holes are the stay bolts that hold the outer
backhead to the inner ring seen in the previous photo.
The device shown in the previous drawing that controls air flow to the
boiler fit over the large hole in the bottom of the backhead. It was
probably removable to allow access to
the combustion chamber. The backhead has not yet been rivited
to the outer shell.
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In this photo you see the backhead after the hand hole
covers have been installed. The shaded objects that cross the hand
holes are brackets that pull the hand hole covers tight against the inside
of the backhead. There were 40 on this backhead.
It is unlikely that any appliances were mounted to the backhead in that
they would block access to the hand holes needed to clean out the tubes.
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This paint drawing shows probable hand hole detail.
Drawing is not to scale. Tubes were 3 inches in diameter. It
is likely that hand holes were oval (to get the flange through the hand
hole from the outside) and in the range of 3 1/2 by 4 1/2 in
diameter. Variance in width and height would depend on width of
flange. A gasket (not shown) would seal the hand hole cover against
the inside of the backhead. |
The following photos are blown up from photos appearing on the previous page
and concentrate on backhead detail visible through the cab windows. These
are all in service shots.
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This is Bill Thomas sitting in the engineer's seat.
Yes, the engineer sat on the right when facing toward the front of the
engine.
The nearer larger of the two pipes feed brings feedwater to the
injector. The smaller pipe takes overflow from the injector and
exhausts it out of the bottom of the engine. The injector would also
have received steam from a steam line from the above turret providing the venturi effect that
would inject water into the boiler.
It is likely there was a second feedwater injector on the fireman's
side. Tender photos show that there were redundant water lines running from
the tender along the running boards in both the left and right side of the
engine.
Click photo for a larger image. |
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For comparison with the above photo, here's a picture of an
Edna injector from David Fletcher's MasterClass 2001 series. As you
can see the water line and the overflow line come from below, just as in
the above photo. The water to the boiler exits horizontally from the
injector. In the above No 21 photo, the water exits the injector to the rear
(behind Bill Thomas' head). This pipe continues along the seam
between the steam chest and the boiler to the other side of the steam
chest. It is likely injection occurs from the tender side into the lower part of the steam chest
through a perforated pipe running laterally through the chest. This
line is the lower line shown in the above drawings. |
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This is a diagram of a typical arrangement for an oil
fired locomotive. Three valves control the distribution of steam.
- Top valve - burner blow through.
- Pipe Heat - Heats the oil just prior to injection.
- Atomizer - Atomizes the fuel just prior to injection.
Click drawing for a larger image. |
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This shot clearly shows three valves just to the left of the
fireman's head.
The steam line in the above photo is likely to drop down from the steam
chest area.
The thick horizontal tube is likely to be the steam
manifold. |
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The leftmost device in this photo is the hydrostatic
lubricator feeding steam oil to the cylinder on the
fireman's side of the engine. Immediately to its right is the
hydrostatic lubricator feeding steam oil to the cylinder on the engineer's side of
the engine. The lines coming in from the top are the steam lines
from the turret feeding the hydrostatic lubricators.
Click the photo for a larger image. |
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This is a photo of a hydrostatic lubricator from David
Fletcher's MasterClass 2001 series. The copper line from the bottom
of the lubricator feeds oil to the piston. The top line is oncoming
steam from the turret. The bottom wrapped line controlled by a valve
allows condensed water in the lubricator to be drained. |
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This photo is not at all clear.
Click photo for a larger image. I would appreciate any theories
anyone has as to what we're looking at through the engineer's window in
this photo. |
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These three photos are from David Fletcher's MasterClass
2001 series. The left handle controlled the Westinghouse Brake
system. The right handle controlled the engine brakes. These
would have been mounted to the right of the engineer. |
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It is likely each brake system had a gauge although some
engines had a single gauge that displayed both readings. The
partially hidden gauge on the left displays boiler pressure. |
It is likely that there were one or two steam pressure gauges. Readings are
likely to have been taken from the lower portion of the steam tube. A
copper wire would have routed water to the pressure gauges mounted at a level
that would have been visible to the engineer and fireman.
A turret also would have been somewhere in the backhead area to provide steam
to various accessories. It would have been fed by a steam line from the
upper portion of the steam chamber. The reason we don't see it in photos
is it may have been mounted high enough that it was invisible in these
photos. This is supported by the fact the steam lines for the injectors
and hydrostatic lubricators appear to come from above.
All of us owe a big thank you for Keith Christenson who was of tremendous
assistance in nailing down this backhead detail.
Keith commented on the fact that the NPC moved the whistle after No 21 was
outshopped. He theorizes that water sloshing in the steam tube caused the
original whistle to occasionally malfunction, requiring a change in mounting
point.
Keith also feels that the comments relating to fire glowing through seams in
the firebox was actually blowback from the burners through the air intake holes
in the cab. It is possible that the hole cut in the front of the cab after
outshopping was a shroud that covered the air intake reducing the possibility of
fire in the cabin.
Backhead Drawing
Based on the information contained in these photos and David Fletcher and
Kieth Christenson's combined steam engine knowledge, Fletch prepared CAD
drawings of No 21's backhead. The Backhead
Drawing page, goes through these drawings in detail.
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