Assembling the Parts

 

In tackling the assembly of the components that I printed as described in Part 2 of this series, I was reminded of President Kennedy’s words “We choose to … do the other things, not because they are easy, but because they are hard“

 

I had realised that the assembly of the parts was not going to be easy but it turned out even trickier than I had expected. To re-cap, the parts I printed were as shown below:

 

3D printed Atmospheric Apparatus Components

 

The tricky aspects arise from the need to align the four axle bearings with the appropriate axles. The locations of these axles are, in turn, determined by the placement of the axle boxes on the main carriage under-frame.

 

My idea was to suspend the hangers, which carry the cylinder frame and the two cylinders, from a brass rod passing across the centre of the octagon. The inboard ends of the longitudinal frames have sockets to accept the ends of this brass road, thus holding together the entire upper part of the apparatus. I included holes in the octagon and hangers, plus sockets in the longitudinal frames, within the 3D models of these components and, rather to my surprise, they actually appeared as required from my basic 3D printer.

 

A little opening out with a reamer was all that was required to enable a 1mm brass rod to pass through the octagon and the hangers, as I had intended. This stage of the assembly is shown below:

 

Octagon, with Hangers suspended from Brass Rod

 

In this photo above, the octagon is actually upside down, as I soon realised, but it does show the method of assembly quite clearly. I used superglue to attach the lower ends of the hangers to the piston frame, then clamped these parts together to allow the glue to harden.

 

Next, it was time to press the longitudinal frames onto the ends of the brass rod and align the whole assembly with the axles of the carriage wheels. At this point, I realised that the octagon was upside down and also that the brass road had to be removed to allow the central axle to pass through the bearings on the octagon – now turned downwards.

 

Getting everything to fit together proved to be something of a trial! [understatement] The parts are small and it was difficult to hold every thing still, in order to set up the correct alignments. Fortunately, the brass rod was quite a firm fit into the ends of the longitudinal frames, so this helped me to wiggle everything into place, without it all falling apart.

 

I think some more thought about this part of the assembly might result in a better method but we are where we are! After a certain amount of cursing and swearing, the assembly looked like this:

 

Atmospheric apparatus attached to Carriage Chassis

 

It was a great relief when I found that the sloping longitudinal frames did not clash with the lateral parts of the carriage frame, although it was close! My 3D model proved itself to be accurate!

 

When in the operating position, the piston carriage hangs below the level of the running rails but, in my model, it is hinged like the prototype, so it can be swung to one side to allow this vehicle to run on normal track.

 

All that remained was to attach the two pistons, connected by a brass piston rod to the piston carriage and the model was complete – hurrah!

 

My 4mm scale 3D-printed model Piston Carriage

 

On the evidence of the contemporary paintings by William Dawson, it seems most probable that the carriages were painted brown overall, so I have adopted this colour for my model.

 

After fettling, painting, and general ‘tidying up’ of the model, I posed it on my short length of broad gauge track. The roof is covered in self-adhesive vinyl. I used a leather punch to create holes in the vinyl for the oil lamp housings. The windows are glazed with overhead transparency sheet. The piston for the atmospheric apparatus can be seen below the front buffer beam of the carriage.

 

My 4mm scale model of SDR Piston Carriage

 

 

The Atmospheric Train in Operation

 

To add a sense of realism to the scene, I placed a few of my models against a back-scene representing the red sandstone cliffs at Dawlish Warren:

 

 

Diorama showing some of my Broad Gauge models

I think it might be useful to add a few notes on how the trains were operated and how the pistons under the carriage were inserted into the propulsion pipe.

 

The first point is that the system was designed for single-line working only. Because the flap valve was hinged to one side of the slot along the top of the pipe, it had to be raised by the apparatus below the carriage from the side opposite to the hinge. Research by the BGS strongly suggests that the hinge ran along the ‘seaward’ side of this coastal railway, from which it follows that the lifting apparatus must work from the landward side. Surprisingly, the protective metal covers, shown in Samuda’s Patent illustrations, were not fitted, despite the obvious detrimental effect on the leather arising from the seaside environment.

 

Patent Illustration showing hinged leather seal

 

Because of this ‘handed-ness’ the carriage always had to work in one orientation and could not be turned. That is why there had to be two pistons and driving compartments at both ends. Brakes were only fitted to the wheels on the landward side, so the drivers position was towards that side, where the brake operating levers were situated.

 

The propulsion pipes were laid in 3 mile lengths, each length attached to a pumping station. Flap valves at the ends of the pipe were opened in response to a trigger device, operated as a train approached the end of one of the pipes. Once the pistons had entered the evacuated pipe, the driver had no means of regulating the speed of the train other than by applying the brake.

 

The propulsion pipes stopped short of stations and the train ‘free-wheeled’, in the manner of a slip coach, after leaving the pipe until stopped, hopefully at the station platform, by the driver. Under- and over-runs were apparently not infrequent. At that time, manhandling or horse-shunting of railway vehicles were not unusual and these were, in general, the only methods available, if the train had to be moved when ‘off’ the pipe.

 

The exception was for starting a train from a station. An auxiliary pipe was laid alongside the track ahead of each station. This pipe contained a piston attached to a length of rope that could be hooked to the front of the piston-carriage. The rope started the train into motion until the pistons entered the main propulsion pipe, when the driver released the staring rope. The flying end of the rope was a potential hazard to any gangers that might be near the line at the time!

 

Before the train could start, the pumping engine for the appropriate section of pipe had to be operated. This was done according to the timetable so, if a train was late, the pumps had to be run for much longer than was strictly necessary, which increased the costs of running the system. Curiously, although the electric telegraph was installed along the line, it was never used to signal when the pumps were needed!

 

Whenever the piston carriage had to be taken off the main line, its atmospheric apparatus had to be raised, in order to clear any pointwork and crossings. This was achieved by use of a winding handle fitted into a socket on the seaward side of the carriage.

 

All these factors were clearly inconvenient, when compared with the flexibility of steam locomotive working.

 

For any one who wishes to learn more about this railway, I can recommend the book ‘Brunel’s Atmospheric Railway’ which, apart from containing the set of 25 contemporary watercolour illustrations by William Dawson (1790-1877), provides extensive text and drawings, edited and produced by Paul Garnsworthy of the Broad Gauge Society (BGS). A new edition has recently been printed.

 

Addendum

 

Robert Stephenson carried out a technical review of the Kingstown & Dalkey atmospheric railway in Ireland in 1844.

 

Kingstown & Dalkey atmospheric railway

 

His conclusions were:

 

1st That the atmospheric system is not an economical mode of transmitting

power, and inferior in this respect both to locomotive engines and stationary

engines with ropes.

 

2nd That it is not calculated practically to acquire and maintain higher

velocities than are comprised in the present working of locomotive engines.

 

3rd That it would not in the majority of instances produce economy in the

original construction of railways, and in many would most materially augment

their cost.

 

4th That on some short railways, where the traffic is large, admitting of trains

of moderate weight, but requiring high velocities and frequent departures, and

where the face of the country is such as to preclude the use of gradients suitable

for locomotive engines, the atmospheric system would prove the most eligible.

 

5th That on short lines of railway, say four or five miles in length, in the

vicinity of large towns, where frequent and rapid communication is required

between the termini alone, the atmospheric system might be advantageously

applied.

 

6th That on short lines, such as the Blackwall Railway, where the traffic is

chiefly derived from intermediate points, requiring frequent stoppages between

the termini, the atmospheric system is inapplicable ; being much inferior to the

plan of disconnecting the carriages from a rope, for the accommodation of the

intermediate traffic.

 

7th. That on long lines of railway, the requisites of a large traffic cannot be

attained by so inflexible a system as the atmospheric, in which the efficient

operation of the whole depends so completely upon the perfect performance of

each individual section of the machinery.

 

I remain, Gentlemen,

Your most obedient servant,

ROBT. STEPHENSON.

 

Stephenson’s assessment, especially his 5th point, is being re-applied with modern technology in both Indonesia and Brazil. See https://www.youtube.com/watch?v=GM2Zxn7ybNQ

 

 

Mike