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LNER Route: Leicester to Marylebone
Rugby Central Station: gcrcs197
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An LNER built K3 Class 2-6-0 locomotive is silhouetted
against the morning sun whilst crossing the GCR viaduct just north of the
'Birdcage'. The concept for the K3 2-6-0 began in August 1917 when Gresley
started to consider a new express goods engine for the Great Northern Railway
(GNR) based on his K2 2-6-0 (GNR Class H3), but with a higher boiler pressure
of 180psi and 20in or 20.5in diameter cylinders with a 28in stroke. The greater
piston loads resulted in a lot of attention being given to the coupling rod pin
bearing surfaces which would have had to have been increased. This is thought
to have been the main reason for the scheme being eventually dropped. By this
time, Gresley's three cylinder O2 2-8-0 mineral locomotive was being built.
This was the first locomotive to incorporate his patent 'conjugated' valve gear
on the middle cylinder, and was quickly deemed a success. Gresley announced
that his future designs would concentrate on three cylinder designs, and turned
his attention to the 2-6-0 express concept from 1917. With three cylinders, he
reduced the cylinder diameter to 18.5in but kept the boiler pressure at 180psi,
with the net effect of an increase in tractive effort of 36 per cent over the
K2s. The boiler was enlarged to a then-unprecedented 6ft diameter, in order
provide an adequate supply of steam. The outside cylinders were almost
horizontal, but the inside cylinder was steeply inclined to clear the leading
coupled axle.
Although very similar to the K1s and K2s, the K3s looked
different due to their large diameter boilers and stout boiler mountings. The
cab continued the austere style started by Ivatt. No side windows were
provided, but a 1ft 6in deep side cut-out was provided as a driver look out.
The roof also extended back 9in over the cab entrance. Later batches of K3s
would introduce side windows and padded seats to the design. The first ten
locomotives (Nos. 1000-9) were constructed between 1920 and 1921. Their advent
coincided with the coal strike of 1921. Although intended for fast goods work,
the strike meant they they were often used on express passenger services as an
economy measure. The K3s managed this very well, and quickly made a name for
themselves hauling trains up to twenty bogies in size. Jazz music was just
becoming popular in Britain at that time, and they quickly earned the name of
"Jazzers" due to their syncopated exhaust beat and uneven gyratory movement at
the rear. The exhaust beat was a side-effect of the three cylinder design, and
would become a common sound with the advent of further Gresley types.
The poor riding, however, would pose problems for
maintenance. Early testing showed an over-travel problem on the middle valve
during high speed coasting. This was partly due to the design of the conjugated
gear multiplying any slackness in the pins and joints, and partly due to a whip
action in the motion levers at speed. The problem was avoided by limiting the
maximum cut-off to 65 per cent. The K3 became a Group Standard design quickly
after Grouping in 1923, and in total 193 locomotives would be built in seven
batches between 1920 and 1937. Construction only stopped after the new V2s had
proven themselves as good replacements. Each batch would show minor
refinements, so between 1923 and 1935 each batch was classified chronologically
by its part number, e.g.. the 1920/1 batch was K3/1, and the 1934/5 batch was
K3/6. Due to the differences being deemed minor in nature, classes K3/4, K3/5,
and K3/6 were merged in with K3/2 in 1935. The original ten K3/1s were built to
the larger GNR loading gauge, but were reclassified as K3/2 when they were cut
down to the Composite LNER loading gauge. The last K3/1 was cut down and
reclassified in 1940. Usage of the K3/2 and K3/3 class parts was discontinued
with Nationalisation in 1948.
Courtesy
LNER
Encyclopedia
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