N7  69600 – 69733  0-6-2T  GER & LNER  Hill & Gresley

n7

Power Classification 3MT
Introduced 1914 – 1928
Designer Hill and Gresley
Company GER and LNER
Weight N7/1 63t 13cwt, N7/2 64t 17cwt, N7/3 64t 0cwt and N7/4 61t 16cwt
Driving Wheels 4ft 10ns
Boiler Pressure 180psi superheated
Cylinders Inside – 18in x 24in
Tractive Effort 20,515lbf
Valve Gear Inside Walschaert (piston valves)

 

Although the Great Eastern Railway’s (GER) London suburban services were amongst the most intense and heavily loaded in the country, the GER operated them with relatively small 2-4-2Ts in the early 1900s. On an average weekday in the period 1910-14 there were over 1,200 movements into and out of Liverpool Street terminus. It was a slick operation, and one undertaken with manual signalling and a fleet of modestly powered locomotives. Chief amongst these were the small 0-6-0T engines designed by Holden which daily climbed of 1 in 70 up to Bethnal Green with packed ten-coach commuter trains.

 j69 small LNER class J69 introduced by Holden on the GNR in 1902 for suburban services
 n7 small LNER class N7 as introduced by Hill on the GNR in 1914 as GNR class L77

The GER had considered electrification in 1902 but this was soon abandoned. To handle the heavier loads, Holden produced a plan for an 0-6-2T in 1907. This was never built, and it was not until 1915 that Hill built two 0-6-2Ts to handle the heavier loads. Superheating was still a new concept so one was superheated as a comparison. GER 1000 (69600) was built with a saturated boiler, and GER 1001 (69601) was built with a 12-element Robinson superheater. These two locomotives formed the GER class L.

The driving wheels had a relatively small diameter of 4ft 10in, 4in smaller than those on the earlier F4. Walschaerts valve gear, piston valves, and a Belpaire firebox were fitted. Intended to replace a range of 0-4-4Ts and 2-4-2Ts, the N7 had a controlled side traverse to the leading coupled axleboxes in order to provide some flexibility in the wheelbase. This was similar to the mechanism used on the trailing powered axle on the B12. With the same number of axles as the earlier locomotives but with a heavier total weight, the N7s represented a significant increase in adhesive weight.

The boiler was built with two telescoping rings with the larger diameter ring at the front. Both of the original locomotives were fitted with twin anti-vacuum valves on the smokebox behind the chimney, for use with piston valves. On the superheated locomotive, they also performed the function of admitting air to the elements. The boiler feed was using Churchward’s arrangement with clack valves on either side of the dome. Four-column Ramsbottom safety valves were fitted in a rectangular casing.

With the outbreak of the First World War in July 1914 no further locomotives wwere built until ten more saturated N7s were appeared in 1921, and were followed by ten superheated examples in 1923-4. These were all to the original GER design, although the superheaters were increased in size to 18 elements. All of the GER sanctioned locomotives were built at Stratford.

The N7 design impressed the LNER and it was adopted as a Group Standard to complement Gresley’s N2 0-6-2T design. The N7s had small wheels and were able to accelerate quickly, making them ideal for suburban services between closely-positioned stations.

When the LNER was formed in 1923 the Chief Mechanical Engineer (Nigel Gresley) was quick to see the potential of the design. By this time only 15 N7 class locomotives were in service and the improvements made to the track and signalling had allowed Liverpool Street suburban services to increase very significantly (75 increase during early morning rush hour services).

The LNER built a total of 112 Group Standard N7s between 1925 and 1928 in five batches. These were built at Gorton, Robert Stephenson, W. Beardmore, and Doncaster. By this point, the LNER had stopped building new locomotives at Stratford due to high London wages, and under pressure from the Government who were trying to solve unemployment problems further north. The LNER engines were intended for work in the south and had their boiler mountings and cab cut down to fit the Metropolitan City Widened Lines. They were also left-hand drive.

Condensing gear was fitted to all of the GER locomotives, but was removed from many locomotives during LNER ownership. Some kept their condensing gear for working the East London line via the Thames Tunnel. The remaining condensing gear was removed from all N7s between 1935 and 1938.

The LNER added a number of modifications to the later batches. Long travel valve gear and a pony trucks were fitted on the last 72 N7s. The last 32 were built at Doncaster and had Doncaster-style round-topped fireboxes, instead of the original Belpaire design. The round-topped boilers were in line with contemporary LNER practice, and were also fitted with 18-element Robinson superheaters.

The LNER had constructed five spare 18-element superheated boilers before the round-topped boiler was adopted. From 1928, these were fitted to the saturated engines. The remaining saturated locomotives were altered to carry 18-element superheaters; and No. 1001’s 12-element superheater was upgraded to 18 elements. By September 1931, all 22 GER N7s were fitted with 18-element Robinson superheaters.

The round-topped boiler design became the N7 standard, and was used for all boiler replacements after 1940. Eventually all except two of the Belpaire locomotives would be rebuilt with round-topped boilers.

Many of the later boilers were fitted with Ross pop safety valves instead of the original Ramsbottom valves.

The positioning of the Walschaerts valve gear proved to be problematic. The cramped location resulted in less than ideal linkages and heavy forces acting on parts of the gear. The combination lever pins experienced heavy wear, and the anchor bracket bolts often failed. The problem with the bolts was only solved in the early 1940s when the bolts were replaced with a weld between the anchor bracket and the crosshead. The locomotives with long-travel valve gear also experienced bent valve spindles and even breakage of the anchor bracket. This resulted in a redesign of the bracket for long-travel valve gear locomotives.

The N7 valve gear also suffered under the GE Section practice of coasting with the engine in full gear followed by a sudden change in cut-off at speed. This would often result in a complete failure in the valve motion. During the 1930s, the GE Section had a campaign that attempted to get drivers to coast at half cut-off. This reduced the failures, but they still occurred occasionally. After No. 69721’s valve gear disintegrated at speed in 1956, the N7s with long travel valve gear were fitted with larger diameter valve spindles and heavier valve guide bushes.

Six sub-classes were used to cover the various variations.

  • The N7 class consisted of the original 22 GER engines (69600-69621). These were fitted with Belpaire fireboxes and short-travel valves and were fitted for right-hand drive. They were later rebuilt with Gresley round-topped boilers and classified N7/4
  • The N7/1 class consisted of the LNER engines which were built in 1925-6 (69622-69671). These engines were built with left-hand drive and fitted with the Metropolitan line loading guage. They had some detail differences from the N7s but they were also fitted with Belpaire fireboxes and short-travel valves. They were later rebuilt with Gresley round-topped boilers and reclassified N7/5.
  • The N7/2 class consisted of thirty LNER engines which were built in 1927 (69672-69701). They were fitted with long-travel valves and redesigned Walschaert valve gear but they still retained Belpaire fireboxes. They were fitted with pony trucks instead of radial axle-boxes and they were fitted with higher bunkers without coal rails. Most were later rebuilt with Gresley round-topped boilers and reclassified N7/3.
  • The N7/3 were the last batch of engines (69702-69733) and were built new at Doncaster with Gresley type round-topped boilers in 1927-28. The N7/2 engines were also classified N7/3 when rebuilt with round-topped boilers from 1943 onwards.
  • The N7/4 class was the original N7 class when rebuilt from 1940 onwards with Gresley round-topped boilers.
  • The N7/5 engines were the N7/1 engines which were rebuilt from 1943 onwards with Gresley round-topped boilers.

Ten locomotives were fitted with push-pull control apparatus.

The first two locomotives, Nos. 1000 and 1001, were initially put to work on the Enfield and Chingford lines. By 1921, the first twelve engines were being used on the heavier or faster suburban trains operated by the Stratford shed. The next batch were distributed between the West Riding, Stratford, and Hatfield. The four allocated to the West Riding were re-allocated to Neasden during 1924 and 1925 to haul services to the British Empire Exhibition at Wembley. The later Group Standard locomotives were allocated to GN and GE Section suburban services in the London area. As well as the heavier and faster suburban services, the N7s also hauled evening excursions. They were also used on the boat trains from Liverpool Street to Royal Albert Dock.

After World War 2, electrification and the introduction of large numbers of L1 2-6-4Ts resulted in a number of N7s leaving the London area. Allocations away from London were initially to Ipswich, Melton Constable, and Norwich. A number of other allocations to country sheds occurred during the 1950s, including Cambridge, Lincoln, and Staveley. During 1954, four N7s were allocated to Leeds-Bradford and Leeds-Castleford push-pull services as a stop-gap whilst newly introduced diesel multiple units (DMUs) had their teething problems fixed.

The N7s survived on their original suburban London services until displaced by the introduction of DMUs and electrification in the 1950s.

69614 was based at Stratford from September 1951 until it was withdrawn from service in December 1960. This locomotive was used as station pilot at Liverpool Street and was always turned out in pristine condition.

Withdrawals started in 1957 and were complete by 1962.

Number in Service.

Built Withdrawals No. in Service
BR Numbers Quantity
1914 69600-1

  2

    2

1921 69602-11

10

  12

1923 69612-14

  3

  15

1924 69615-21

  7

  22

1925 69622-31 & 69652-69

28

  50

1926 69632-50 & 69670-71

21

  71

1927 69651, 69672-77 & 69682-712

38

109

1928 69678-81 & 69713-33

25

134

1929-57

134

1958 12

122

1959 40

  82

1960 45

  37

1961 28

    9

1962   9

    0

  • 69600-69621 were built at Stratford
  • 69622-69651 and 69672-69681 were built at Gorton
  • 69652-69671 were built by Robert Stephenson & Co Ltd
  • 69682-69701 were built by Beardmore Ltd
  • 69702-69733 were built at Doncaster

Locomotive allocations during British Railways operation

Depot as at 1st January

1948 1952 1957 1959 1960 1961

1962

Annesley

2

Bishop Storford

1

1 1 1 1

1

Buntingford

2

2 2

2

Cambridge 2

1

Colchester 4 2

8

Colwick

3

Enfield Town

14

14 14 14 7 4

1

Hatfield

8

7 15 13 11

7

Herford East

11

11 10 10 9

1

Hornsey 4 3

1

Kings Cross

5

Kings Lynn 1 3

1

Lowestoft 1

3

Norwich Thorpe 5 2

1

Palace Gates

2

2

Parkeston 3 5 2 4

3

Wood St Wallthamstow

14

14 14 8

1

Southend Victoria

2

2

Stratford

80

59 55 51 47 21

8

Tilbury

3

Yarmouth South Town 3

2

134 134 134 122 82 37 9
  • Buntingford in Hertfordshire was the end of a short branch line from the Liverpool Street to Cambridge line. There was a direct rail service from Liverpool Street to Buntingford until 1960.
  • Wood St Wallethamstow depot was a small sub shed of Stratford which from the 1920s the only engines based here were class N7 tank engines for working suburban trains into Liverpool Street. The shed was closed in 1960 when the line was electrified.
  • Palace Gate depot was a very small sub shed of Stratford which was on a branch line off the Liverpool Street to Enfield line. The depot closed in 1954.

 

Preservation

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