6023 King Edward II Project

The King class was the final and most powerful development of the GWR’s 4 cylinder designs. GWR CME (Chief Mechanical Engineer) Charles Collett’s Castles were arguably the GWR’s finest passenger engine design, and on a tractive effort basis, had proved themselves more powerful than LNER’s Flying Scotsman. Nevertheless, the advent of the Southern Railway’s King Lord Nelson class as the new leader in British express steam tractive effort (33,500lbs) pushed the GWR’s publicity office to push for one greater engine class, with a nominal tractive effort of 40,000lbs.

The apparent need for such a class existed on the heavily graded routes in South Devon, en route to Plymouth. However the ‘hammer blow’ of the weight of each axle plus the effect of reciprocating parts was expected to be in the region of 22½ tons, 3 tons in excess of the 19½ ton static design limit of most GWR bridges. Luckily, across the huge and unwieldy GWR organisation, the civil engineering division had been independently raising the bridge loadings to 22 tons for the previous 22 years, and a concession of 22½ tons was made for 4-cylinder engines. For 22½ ton axle loading, routes from London to Plymouth and Cardiff, on a handful of bridges would need strengthening. These routes would become the ‘double red’ routes of the GWR, and the Kings would rarely stray from them.

 Collett opted for smaller wheels on the King than his Castles, after casting aside the conventional wisdom that large wheel diameter was needed for the greatest speed. He had observed an express train being overhauled by a mineral train hauled by a close-coupled GWR 4-8-0 with small wheels. When compared with the Castle class, the slightly smaller wheels adopted for the King Class allowed more space above them for a fatter boiler to be built, as little extra engine height was available for expansion.

Nevertheless, such a reduction in wheel size was not without its corresponding problems. A long standing Swindon design constraint imposed by former CME George Jackson Churchward, was that the pistons would be level and not slanted. This meant the centre height of the pistons would be the same as the driving wheel axles. The smaller wheels thereby lowered the height of the pistons. At the same time, to achieve the 40,000lb tractive effort, the pistons were enlarged to 16¼” bore and 28” stroke. The outer pair of pistons, acting on the centre wheels, needed to hang either side of the rear wheels of the front bogie. The hidden inner pair of pistons, acting on the front set of driving wheels, hung low between the front wheels of the bogie. Both factors meant a traditional springing arrangement for the bogie was impossible. A compromise design with the front wheels sprung on the outside and the back wheels of the bogie sprung on the inside, produced the distinctive and decidedly odd-looking long front bogie of the Kings.

Like on the Stars and Castles before them, the Walschaerts valve gear was concealed between the frames, and driven off the front set of driving wheels. The two inner valves, directly above the inner pistons, were driven directly from these sets of valve gear. The outer valves, directly above the outer pistons, took a reflected drive from the inner valve gear via a pair of rocker arms emerging from the frames above the front bogie. Like the Stars and Castles, no external valve gear was visible, but this aesthetically pleasing arrangement made for a maintenance nightmare, with over 120 oiling points, many hard to reach, before the engine could take to the road.

Draughting arrangements included a 'jumper' blastpipe ring (the blastpipe is inside the smokebox and directly under the chimney - it directs the steam exhaust straight up into the chimney and in doing so creates a strong sucking action on the fire in the firebox, drawing the hot gases through the tubes of the boiler.) A jumper ring was designed to allow the blastpipe to lift and expand under heavy working.

The first member of the class, 6000 King George V, left Swindon in 192-, and after running in was sent to represent the GWR at the 100^th Anniversary of the Baltimore & Ohio Railroad. It returned with a memorial bell that it wears to this day. Subsequent class members were named after Kings of England in reverse order from King George V. 

Trials proved Kings to be only marginally better than Castles on gentle gradients, but the Devon banks proved their mettle. 

The principles of the King design did evolve further, but not on the GWR. Collett’s assistant William Stanier became CME of the London Midland and Scottish Railway, and improved the design by having four full sets of valve gear, and a longer boiler with a wide firebox over lowered rear frames supported by a rear bogie. These giant 4-6-2 Pacifics were his Queen Elizabeth Class, further improved in the shape of the magnificent Duchess class. 

The Kings played an important part in the evolution of British Express steam locomotives, but their further development within the GWR was unnecessary as the need for a more powerful express engine was not justified. The long runs from London to Scotland provided the need for bigger engines with more speed and more stamina, but these routes were under the LNER & LMS.

All GWR engines were designed for Welsh Steam Coal, with its high carbon content and low proportion of volatile gases. Poor coal quality during World War 2 forced changes in the draughting arrangements soon after the war, and the removal of the jumper ring and replacement with a larger plain blastpipe was found to improve performance on the poorer coal available, which had a high amount of volatile matter in it.

After 1956 the Kings were fitted with a double blastpipe and narrower double chimney draughting arrangement. Four row superheater elements were fitted to give a greater level of superheat. Performance shot up, with power rising by 20% at speed, and an 8% improvement in coal and water consumption.

6023 is to be returned to 'Single chimney' condition, unlike its sister 6024, which retains the double chimney and blastpipe..