Heavy and Light Pacific’s
Oliver Vaughan Snell Bulleid – 19/09/1882 – 25/04/1970. Born in Invercargill, New Zeeland to immigrant British parents. We felt that as this is the 50th anniversary of Bulleid’s death it would be appropriate to explore some of this noted engineers’ achievements during the second world war.
At the outbreak of The Second World War Oliver Bulleid had been employed as Chief Mechanical Engineer for The Southern Railway (SR) since 1937. During his time with SR he developed many well-known locomotives. It was during 1938 that Bullied gained approval to build the Merchant Navy and West Country class of modern 4-6-2 Pacific locomotives.
Bullied had worked and trained under Gresley, and for a time had travelled Europe whist he worked with the Board of Trade. Bulleid drew on these experiences when he was drawing up the designs for the new 4-6-2. He employed all of the most up to date equipment in these engines, incorporating partially welded boiler’s and fire box’s, forgoing the traditional original rivet design.
He also employed Thermic Syphon’s. These are heat exchange elements incorporated into the fire box and combustion chambers of the steam boilers, because these elements are directly exposed to the radiant heat of combustion they have a high evaporation capacity relative to their size, and if arranged vertically they also provide very good water circulation by means of this thermo-syphon effect, circulating the water by passive heat exchange based on natural convection ( a method employed today in solar water heaters ). This provided the 4-6-2 locomotives with a complex but compact and lightweight means of increasing boiler capacity.
Bulleid believed that it was better that the working parts of a steam locomotive were not exposed to the open air and elements. He wanted to draw steam locomotive design closer to the internal combustion engines which enclosed working parts and pumped lubricants to enable smooth running.
To this end he designed and patented the radial chain driven valve motion, which he immersed in an oil bath. Unfortunately design errors in the casing for this caused leaks to form over time, this was problematic if the valve gear was not maintained properly and was of course an extra difficulty under war conditions. Bulleid aimed for a boiler pressure of 280 lb the highest ever used in England, the barrel of the boiler was tapered but on the base side only. All SR Locomotives designed by Bulleid are fitted with B.F.B ( Bulleid Firth Brown ) a complex form of disc wheel which gave an even tyre support. In America similar wheels are known as Boxpok wheels, however these are of segment construction unlike the BFB which is one solid casting. Instead of spokes the wheels have contoured solid struts throughout the wheel, rendering them shatter proof, extraordinarily strong and easy on track ware. These wheels did not completely eliminate the need for balance weights on the wheels however combined with the setup of the Bulleid valve gear, and 3 cylinder layout it did eliminate wheel hammer blow. Later, when some of the locomotives were retro fitted with Walschaerts valve gear, balance weights had to be added to the 4-6-2 engine wheels. They also featured multi-jet exhausts.
The whole simple locomotive was streamlined and encased and was fondly named the “Spam Can” after its resemblance to the oblong can of “SPAM” luncheon meat.
The first Merchant Navy Pacific 4-6-2’s were introduced in early 1941 and as the first ten emerged from the Eastleigh works, they were named after well-known shipping lines. The very first was Merchant Navy 21C1 Channel Packet after this a further 39 were built, the last one being Pacific 35030 Elder Dempster Lines. A remarkably similar but slightly smaller lighter version Pacific as also designed utilizing the same mechanical principals, but with a higher route availability, enabling them to be used on lighter track as found on some secondary routes. The complete class of this lighter type of locomotive amounted to 110 and they too were classified not as passenger locomotives but mixed traffic motive power. Many the class bore the names of the West Country towns and cities in the area’s they served; hence the Class were referred to as the West Countries. Later, some were named after wartime aerodromes, squadron’s or famous war leaders, for example “Biggin Hill”, “Squadron” and of course “Winston Churchill” which hauled his funeral train. These so named members of the class became a sub-class The Battle of Britain Class.
Bulleid also designed the SR Q1 an SR Austerity type 0-6-0 tender engine (A truly Ugly engine) for the War Effort.