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Bulleid’s Design and Vital Statistics

The  Innovations - and What Became of Them.


Wartime  photograph, believed to be 21C8 "Orient Line" passing Surbiton  September 1942
Photo by : Dr. T.F. Budden


The  boiler was designed for a working pressure of 280lb/sq in, later reduced  to 250. To reduce weight and cost, a welded steel firebox was fitted,  as was then common practice in America and Europe. It incorporated two  thermic syphons; although their contribution to steam production is not  proven, they are a safety aid as they promote circulation of water. The  first fireboxes suffered from cracking and had short lives, but the introduction  of comprehensive water treatment eliminated the problem. An important  advantage was that minor repairs were, and still are, carried out using  coventional welding equipment.


The  boiler being lowered onto the frames after its 1990/94 Overhaul

Photo:  R.Sewell

The boiler barrel is tapered, which is not immediately obvious because  unlike most tapered boilers it is horizontal at the top instead of the  bottom. The smokebox was a fabricated structure shaped to fit the space  available. At the rebuilding it was replaced by a cylindrical box. This  boiler is regarded as the best steam-raiser ever fitted to a British locomotive.  Its maximum output is more than the engine can use, and almost the only  thing it will not tolerate is the practice, common on some other railways,  of trying to operate it with the water level above the top nut of the  gauge-glass.

Valve  gear.

 Bulleid's decision to have three cylinders, with separate valve gears,  all driving the middle coupled axle, left very little space for the conventional  inside set of motion, and prompted the attempt to design a new motion  layout compact enough to enclose the whole lot in a casing. All three  sets were worked from an auxiliary crankshaft driven by a triple chain  from the axle. This shaft drove both eccentric rods and combination levers,  giving the desired compact layout. The piston valves had no spindles emerging  from the steam chests but were actuated by rocking shafts located between  the valve heads.

The motion and the inside connecting rod were contained in a steel box  between the main frames. About 2in depth of oil lay in the box, and pumps  sprayed it over the various motion joints. None of this was particularly  revolutionary, being borrowed from internal-combustion engine practice,  and in principle it was superb. There was no daily 'oiling round'; it  was protected from the elements and could run 100,000 miles without attention.  In practice, though, it proved unequal to its job, for two main reasons.  Firstly, the box was inadequate; water leaked in, causing corrosion, and  oil leaked out, causing wheelslip and fire hazards. Secondly, the chain  drive was not positive enough for locomotive valve motion; the slack which  could develop in the myriad pin joints of even the finest chain made the  valve movements highly unpredictable. Moreover, a steam reverser was fitted.  If this reverser decided to misbehave, the locomotive seemed to have a  will of its own. For example, if it dropped into full gear, the slackness  in the motion made the valves over-run their nominal full travel and the  locomotive would take off like an unleashed race-horse, putting the fire  out of the chimney and running the risk of a violent high-speed slip.

These antics did not worry the drivers unduly, for the engines were so  powerful and had such phenomenal steam-raising capacity that as long as  the firemen were willing to continue shovelling coal onto the 49sq ft  grate they would keep going. A 'Merchant Navy'-hauled 'Atlantic Coast  Express' once arrived right time at Waterloo with a cylinder cover missing!  It must be remembered that with modifications and careful servicing the  problems were largely brought under control, but the motion was considered  to be the cause of the high specific operating cost of the locomotives.  We have a legacy from the original arrangement in the form of outside-admission  valves on the outside cylinders.


Publicity  photograph of the first post war "Bournemoth Belle" 7th October  1946

Loco  35018 "British India Line"

Photo:  "The Times"


The  Bulleid pacific was instantly recognisable because, instead of the familiar  engine shape, it was clad in a straight-sided casing. This was claimed  to allow pipe runs to be positioned without regard to appearance, and  to enable the engine to be cleaned by putting it through a carriage washer.  In service, it was an unmitigated nuisance. The view from the cab was  poor, while at speed the flat top generated a vacuum which drew exhaust  steam down into the driver's view ahead. Due to the weight-saving drive  it was flimsy, so panels removed by fitters and dumped on the shed floor  quickly acquired premature wrinkles. All sorts of things could happen  under the casing - not least the oil-soaked boiler lagging catching fire.  Once, a driver said that whenever he opened the regulator, the lid of  one of the big horn-guide oil boxes flew open! Eventually they found that  one of the oil pipes was clamped up alongside the pipe which supplied  the steam chest pressure gauge. Vibration had worn both pipes through  where they touched, so the steam pressurised the oil pipe and blew open  the lid. On rebuilding, the casing was replaced by conventional boiler  cladding, but the cab remained in its original form. It is made of much  thinner sheeting than other cabs, and by 1980 the cab on Clan Line was  rusting through. It was rebuilt with galvanised sheet secured with pop-rivets.

Cab  Fittings and Auxiliaries


The  cab of 21C1 "Channel Packet" Note the "Ajax firedoor controlled  by a floor mounted treadle. Photo copyright A.J.Fry

The  'Merchant Navy' is the safest steam locomotive to be built for service  in this country. The firedoor is a patented type with air-holes, intended  to be kept closed except while firing is taking place, thus minimising  the risk of blow-backs. Originally, it was power operated. The blower  is operated by levers, duplicated on both sides of the cab, so that either  driver or fireman can knock it full on instantly without having to step  in front of the firehole. The cab is laid out to be convenient for the  crew. Mr R. E. L. Maunsell. Bulleid' s predecessor, had adopted the practice  of consulting with the enginemen in his cab designs, many years before  the term “ergonomics” was coined, and Bulleid followed his example.

Safety  Valves


Safety  Valves and Whistle Pull (on right)

 Photo: A Davies

Two  Davies & Metcalfe 'Monitor' type live steam injectors arc carried. Clan  Line's present owners have oft-times blessed the performance and reliability  of these injectors, but there was one crisis in their early days. Eastleigh  Works decided to manufacture some replacement steam cones, instead of  buying them, but when these home-made cones were put to use the injectors  failed to start at high pressure. resulting in much vituperation and dropping  of fires. This gave the injectors a reputation of being assembled with  some magic known only to Davies & Metcalfe, a spell which was finally  broken in the 1970s when MNLPS Chief Engineer Andy Davies machined up  a new cone which worked perfectly. The steam supply to the injectors,  brake and other fittings comes from a manifold mounted on the boiler backhead,  but the manifold itself can be isolated from outside the cab by a valve  whose handle may be seen on the front left-hand corner of the firebox  top. All Bulleid pacifies are fitted with a Stone's steam turbo-generator  supplying current at 24 volts for headcode lights, cab illumination and,  originally, lights under the casing to facilitate servicing. Electric  lights were a novelty on a British steam locomotive; after preservation,  Clan Line became the only working locomotive with such a system, and it  is much appreciated by her owners and British Railways engine crews.



35028  at the coaling plant, Stewarts Lane 10th May 1959

Photo:  R.C. Riley

 The Bulleid tender is the only type in Britain to have a curved side profile  to match the standard carriages of its period, thus attempting a visual  continuity between locomotive and train. There were two types, carrying  5,000 and 6,000 gallons of water. The coal capacity of 5 tons was adequate  for Southern requirements, but on modern-day railtours patrons are regularly  entertained by the MNLPS team producing bags of coal from their support  coach and manhandling them into the bunker. The tender is basically a  box welded up from 3/16in sheet steel. As built, it was structurally  weak and cracks or fractures were common. When called on to do repairs  inside the tank, some welders made a practice of cutting a large piece  out of the side to give themselves some light and air, and welded it back  in afterwards. The frames were also weak and tended to splay outwards,  resulting in excessive side-play in the wheels. The 6,000gal tender, No  3342, preserved with Clan Line, showed all the ailments; it received little  attention during latter BR years and when lifted in 1981 the axleboxes  were seen to have been battered to death by the side-play. New axleboxes  (at 1,600 each) and horns were fitted and the frames were reinforced  by two substantial stretchers.


The  Vital Statistics of a Merchant Navy Class Locomotive.


BR  Power Class Designation


Overall  Length

71  ft. 8 in.

Total  Weight

150  tons

Cylinder  Bore

18  in.

Piston  Stoke

24  in.

Valve  Diameter

11  in.

Valve  Travel

6.75  in.

Coal  Capacity

7  tons

Water  Capacity

5700  Imp gallons

Firegrate  area

49  sq. ft.

Heating  Surface

2450  sq. ft

Coupled  Wheel diameter

74  in.

Nominal  Tractive effort

15  tons

Working  Pressure

250  psi


Dual  Braked Vacuum and Air



The  overhaul completed in September 1994 saw some major design changes incorporated  into Clan line. These changes were not undertaken lightly but were in  response to the changing conditions and requirements of today's modern  railway. The coal capacity of the tender was increased from 5 to 7 tons  (nominal) by extending the bunker towards the back of the tender and  platform level water fillers have been fitted. The latter modification  permits servicing in safety under electrified catenery. Air braking  equipment (see photo below) has been fitted to allow the locomotive  to haul modern air braked coaching stock as older vacuum braked stock  is progressively being phased out.


Air Brake Compressor as installed on  28's Tender.

Compressor  mounted on tender. Shown before the doors were fitted


©MNLPS  2012



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