NZR G class (1928)
Encyclopedia
The NZR
G class was a type of Garratt
steam locomotive used in New Zealand, the only such Garratt type steam locomotives ever used by New Zealand Government Railways. They were ordered to deal with traffic growth over the heavy gradients of the North Island Main Trunk and to do away with the use of banking engines on steep grades. They were one of the few Garratt designs to employ six cylinders. A mechanical stoker was used to feed coal into the locomotive.
of the United Kingdom
. These engines had three cylinders (24 inches x 16.5 inches) on each of the two set of engine frames, thus creating a 6 cylinder Garratt. The engines entered service in 1929.
Walschaerts valve gear operated the outside cylinders with the inner third cylinder operated by a Gresley mechanism
. The locomotives proved a disaster on the light NZR tracks. W. W. Stewart, in his book When Steam was King (pp. 98-104) suggested the most likely reason was because the engines were too powerful for the system and also the valve gear mechanisms were complicated. Stewart stated, and existing photos verify, that the design was most unusual in that the coal bunker was carried on an extension to the boiler frame rather than the normal Garratt positioning on the rear engine frame.
The engines operating at 200 psi and delivered 51,580 lbs of tractive effort, which on the lightly laid New Zealand tracks, proved to be too powerful for the drawbars on rolling stock, and broken drawbars occurred wherever the engines ran. Further, the locomotives when hauling a full load, generated such intense heat in restricted tunnels, which are common in New Zealand, that crews refused to work them.
. The trailing engine axle under the cab carried a heavier load than the leading engine trailing axle and experienced continual problems with overheating. Also the coal bunker carried insufficient fuel in-service and this problem was never remedied, because it would have increased the axle loads beyond the light trackage capabilities.
In 1931 the engines were withdrawn from service. Their numerous design faults sealed these locomotives' fate when the K class
was introduced in 1932.
, and some parts were incorporated into six G class three-cylinder Pacific locomotives constructed at Hillside Workshops. The engines were provided with an AB class
boiler, a new roller bearing trailing truck was fitted, also a new cab, and a Vanderbilt tender
of similar design to that of the AB class - although of larger and all-welded construction. All bogies on the engine and tender were equipped with roller bearings, and other modern equipment included power reversing gear and exhaust-steam injectors. The three cylinders retained their conjugated valve gear
from the Garratts, but this gear was rather light in construction and gave persistent trouble in maintaining the correct settings. The locomotives were used in the South Island
mainly on the Christchurch
to Arthur's Pass
section of the Midland line
and mainly in freight service. The class was far from popular and their shortcomings far too numerous to justify the high cost of major improvements.
New Zealand Railways Department
The New Zealand Railways Department, NZR or NZGR and often known as the "Railways", was a government department charged with owning and maintaining New Zealand's railway infrastructure and operating the railway system. The Department was created in 1880 and was reformed in 1981 into the New...
G class was a type of Garratt
Garratt
A Garratt is a type of steam locomotive that is articulated in three parts. Its boiler is mounted on the centre frame, and two steam engines are mounted on separate frames, one on each end of the boiler. Articulation permits larger locomotives to negotiate curves and lighter rails that might...
steam locomotive used in New Zealand, the only such Garratt type steam locomotives ever used by New Zealand Government Railways. They were ordered to deal with traffic growth over the heavy gradients of the North Island Main Trunk and to do away with the use of banking engines on steep grades. They were one of the few Garratt designs to employ six cylinders. A mechanical stoker was used to feed coal into the locomotive.
Introduction
In 1928, New Zealand Government Railways obtained and operated three unusual Garratt locomotives in the 4-6-2 + 2-6-4 layout from Beyer, Peacock and CompanyBeyer, Peacock and Company
Beyer, Peacock and Company was an English railway Locomotive manufacturer with a factory in Gorton, Manchester. Founded by Charles Beyer and Richard Peacock, it traded from 1854 until 1966...
of the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
. These engines had three cylinders (24 inches x 16.5 inches) on each of the two set of engine frames, thus creating a 6 cylinder Garratt. The engines entered service in 1929.
Walschaerts valve gear operated the outside cylinders with the inner third cylinder operated by a Gresley mechanism
Gresley conjugated valve gear
The Gresley conjugated valve gear is a valve gear for steam locomotives designed by Sir Nigel Gresley, chief mechanical engineer of the LNER, assisted by Harold Holcroft...
. The locomotives proved a disaster on the light NZR tracks. W. W. Stewart, in his book When Steam was King (pp. 98-104) suggested the most likely reason was because the engines were too powerful for the system and also the valve gear mechanisms were complicated. Stewart stated, and existing photos verify, that the design was most unusual in that the coal bunker was carried on an extension to the boiler frame rather than the normal Garratt positioning on the rear engine frame.
The engines operating at 200 psi and delivered 51,580 lbs of tractive effort, which on the lightly laid New Zealand tracks, proved to be too powerful for the drawbars on rolling stock, and broken drawbars occurred wherever the engines ran. Further, the locomotives when hauling a full load, generated such intense heat in restricted tunnels, which are common in New Zealand, that crews refused to work them.
Withdrawal
Consequently, the load was reduced and so defeated the purpose for which the Garratts were purchased; namely to operate heavy loads over a vital main line section of the NIMT route, the central section including the Raurimu SpiralRaurimu Spiral
The Raurimu Spiral is a single-track railway spiral, starting with a horseshoe curve, overcoming a 132 m height difference, in the central North Island of New Zealand, on the North Island Main Trunk Railway. It is a notable feat of civil engineering, having been called an 'engineering masterpiece'...
. The trailing engine axle under the cab carried a heavier load than the leading engine trailing axle and experienced continual problems with overheating. Also the coal bunker carried insufficient fuel in-service and this problem was never remedied, because it would have increased the axle loads beyond the light trackage capabilities.
In 1931 the engines were withdrawn from service. Their numerous design faults sealed these locomotives' fate when the K class
NZR K class (1932)
The NZR K class of 1932 was a class of mixed traffic 4-8-4 steam locomotives that operated on New Zealand's railway network. The locomotives were developed following the failure of the G class Garratts...
was introduced in 1932.
Rebuilds
In 1937 the three ill-fated Garratts were dismantled at Hutt WorkshopsHutt Workshops
The Hutt Railway Workshops is a major railway engineering facility in the Lower Hutt suburb of Gracefield in the Wellington region of New Zealand’s North Island...
, and some parts were incorporated into six G class three-cylinder Pacific locomotives constructed at Hillside Workshops. The engines were provided with an AB class
NZR Ab class
The NZR AB class was a class of 4-6-2 Pacific tender steam locomotive that operated on New Zealand's national railway system. Originally an improvement on the 1906 A class, 141 were built between 1915 and 1927 by NZR's Addington Workshops, A & G Price Limited of Thames, New Zealand, and North...
boiler, a new roller bearing trailing truck was fitted, also a new cab, and a Vanderbilt tender
Tender locomotive
A tender or coal-car is a special rail vehicle hauled by a steam locomotive containing the locomotive's fuel and water. Steam locomotives consume large quantities of water compared to the quantity of fuel, so tenders are necessary to keep the locomotive running over long distances. A locomotive...
of similar design to that of the AB class - although of larger and all-welded construction. All bogies on the engine and tender were equipped with roller bearings, and other modern equipment included power reversing gear and exhaust-steam injectors. The three cylinders retained their conjugated valve gear
Gresley conjugated valve gear
The Gresley conjugated valve gear is a valve gear for steam locomotives designed by Sir Nigel Gresley, chief mechanical engineer of the LNER, assisted by Harold Holcroft...
from the Garratts, but this gear was rather light in construction and gave persistent trouble in maintaining the correct settings. The locomotives were used in the South Island
South Island
The South Island is the larger of the two major islands of New Zealand, the other being the more populous North Island. It is bordered to the north by Cook Strait, to the west by the Tasman Sea, to the south and east by the Pacific Ocean...
mainly on the Christchurch
Christchurch
Christchurch is the largest city in the South Island of New Zealand, and the country's second-largest urban area after Auckland. It lies one third of the way down the South Island's east coast, just north of Banks Peninsula which itself, since 2006, lies within the formal limits of...
to Arthur's Pass
Arthur's Pass
Arthur's Pass is a mountain pass in the Southern Alps of the South Island of New Zealand. It marks part of the boundary between the West Coast and Canterbury regions, 140 km from Christchurch and 95 km from Greymouth. The pass lies in a saddle between the valleys of the Otira River, a...
section of the Midland line
Midland Line, New Zealand
The Midland line is a 212 km section of railway between Rolleston and Greymouth in the South Island of New Zealand. The line features five major bridges, five viaducts and 17 tunnels, the longest of which is the Otira tunnel.-Freight services:...
and mainly in freight service. The class was far from popular and their shortcomings far too numerous to justify the high cost of major improvements.