The four-wheeled cement wagons, or “bubbles” as they are popularly known, are iconic of the modernisation of Irish Railways in the 1960s. They are continuously popular subjects for modelling, so in this article a few observations are offered with that use in mind. One hundred and fifty of these wagons were constructed over a period of eight years and most, I guess, are still in service. The batch numbers are as follows:
- 25050 – 25069 (1964)
- 25070 – 25094 (1965)
- 25095 – 25099 (1967)
- 25105 – 25119 (1967)
- 25120 – 25139 (1970)
- 25140 – 25199 (1972)
The sub-plot of the article is about what information can be extracted from the Worldwide Web. With the advent of the web and the digital camera many excellent images have suddenly become publicly available representing an unparalleled information source. Of course, lacking access to the prototype, a lot of “reverse engineering” is necessary to guess how things are. A list of websites used is given at the end of this article: if the reader is not yet computer-literate then find an internet café, order a coffee and get started! I started this work in order to gather information for creating a rake of cement bubbles. The only drawing I had was the one which came with an MIR kit, which is quite good. Then I started searching the web for photographs. What became clear quite quickly was that although these wagons may seem to be standard, there are actually subtle differences which reflect the building batches and modifications carried out in service. These details might seem a bit too trivial for most people, but I believe that a little variation adds considerably to the realism of a rake of standard wagons. My notes on this aspect are as below.
Solebars: it seems as though these wagons have been built with the stronger springs and spring-hangers of the later four-wheeled stock, presumably reflecting their load capacity of 20 or 21 tons. There are many variations of lifting lugs within the class, which may be two, one or none per side and presumably not necessarily the same number on both sides. Likewise the mounting plate for these lugs may be rectangular, notched or absent and in the latter case various stiffening ribs can be seen instead.
Buffers: two types can be seen on the photographs, both massive parallel items. One (older?) type has a smaller base plate which fits inside the open channel section buffer beam. Note that the buffer beam is arranged with the open channel outwards. The larger buffer is attached to an additional plate welded across the webs of the open channel. Whearas the larger buffer has a relatively plain housing, the smaller one is lumpy with a distal bulge on each side of the housing and a flat rectangle on the top surface next to the ram.
Axleguards: most of the axleguards are solid plate items, but some photographs show the earlier fabricated type with a triangular opening on each side of the spring. This can be seen on other wagons of the same era.
Axleboxes: on a few photographs heavily bolted wing-plates can be seen on the side of the axleboxes, while most wagons have plain wings. Earlier wagons had a plain dished end-cover whereas most of the photographs on the web show the Timken boxes with the characteristic triangular three-bolt end plate.
Unloading Valves: on most photographs, two small yellow-painted handles emerge from holes in the solebar, which control the outlet valves from the tank. Although the little holes seem to be provided on both solebars, the handles appear on only one side. I can see no convention as to which solebar the handles should be on, but there seems to be about equal numbers on left and right-handed examples.
Vacuum Cylinder Covers: the cylinders are located at one end of the wagon and protrude slightly above the chassis, necessitating a chequer-plate platform for safe walking over this area. In a large number of examples this plate has been removed, exposing the vacuum cylinders and chassis, which poses an interesting challenge for the modeller.
Unloading Pipe: at the opposite end of the wagon from the brake system is the unloading pipework. The main unloading pipe of 6″ diameter emerges from the decking at about 60° and is provided with a loose cover, which may be either cylindrical or rectangular.
It is debatable how much variation in these details can be seen in one rake of wagons. New wagons would probably have entered service in very uniform condition but over time modifications would have been made and the various batches would have become mingled.
According to advice gleaned from the Irish Railway Modellers web group, the bulk cement wagons have had three liveries so far. Initially they ran in a light-to-mid grey, then were repainted into CIE orange and finally many were given the Irish Cement ivory colour. Of course since the cement is dumped into the top hatch via a loose hose a lot spills over the tank and ditto for the unloading platform. Given some rain this cakes nicely and holds track dust providing a glorious spectrum of very off-white to brown colours, interspersed with patches of virgin white where the cake has flaked off. Many tanks show a haze of light brown over the lower half of the tank suggesting track dirt and/or rust. A competition for the most realistically painted and weathered cement bubble would be in order!
We are told we should try to run our model railways realistically, so with that in mind it is worth examining the photographs for operational purposes. I have read various opinions about how many wagons rakes consist of, namely 12 wagons per rake originally later increasing to 20. Photographs of an unloading operation at Adelaide show the wagons arranged in pairs, i.e. with the unloading pipes towards each other. Presumably this is to allow the unloading pipes to be transferred easily from one wagon to the second. However, most photographs show a more irregular order, presumably after some shunting. Despite the apparent complexity, the air unloading system allows unloading the wagon into a lorry-mounted tank, which must be equipped with a suitable air blower. Thus a large unloading installation is unnecessary and cement can be delivered at a simple siding – see the example at Waterside, page 66 in Ulster Transport in Colour by Derek Young.
For completeness I should mention my understanding of how the unloading system works, based on the information available for BR’s Presflow wagons. “Fluidised bed” is common in industry to make a heavy mass of powder behave like a fluid by pumping high pressure air through it. The bottom of the cement tank is formed into two cones and it seems most likely that compressed air is injected into each via some sort of distributor ring (I’m guessing here) to fluidise the cement in the bottom of each cone. When the valve on the bottom of a cone is opened, the cement flows out into the large diameter unloading pipe, which emerges up through the decking of the unloading platform and into the unloading hose of the terminal or truck. The instructions for the Presflow state that the pipe-work must be purged with air before opening the cement valves in order to clear any water which has collected in the system, which seems wise. Loading is via the large hatch on top of the tank, most likely by gravity and since this is not a closed system, spilllage occurs.
If any reader is able to shed more light on my observations I would be very glad to receive them on email@example.com.
Reference Websites For Photographs
[We hope to have scale drawings of these characteristic vehicles in a future issue. Ed]