NZR G class (1928)

NZR G class (1928)

A G class locomotive in Garratt form.

Type and origin Power type Steam Builder Beyer, Peacock & Co. Serial number BP: 6484–6486 Build date 1928

Specifications Configuration Garratt: 4-6-2+2-6-4 Driver dia. 57 in (1.448 m) Length 69 ft 8 in (21.23 m) Width 8 ft 6 in (2.59 m) Height 11 ft 6 in (3.51 m) Adhesive weight 87.7 long tons (98.2 short tons; 89.1 t) Loco weight 146.8 long tons (164.4 short tons; 149.2 t) Firebox:  • Firegrate area 58.2 sq ft (5.41 m2) Boiler pressure 200 psi (1.4 MPa) Heating surface 2,223 sq ft (206.5 m2) Cylinders 6 Cylinder size 16.5 in × 24 in (419 mm × 610 mm)

Performance figures Tractive effort 51,580 lbf (229.44 kN)

Career Operators NZGR Number in class 3 Numbers 98 - 100 First run 1928 Last run 1931 Preserved 0 Disposition Withdrawn

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.

About 1913, General Manager E H Hiley considered the importing of 10 articulated Garrett engines and 10 Pacifics; however with the success of the NZR AB class and NZR WAB class Pacifics no more was heard of Garretts. Then with the retirement in 1925 of the Chief Mechanical Engineer E E Gillon his successor G S Lynde invited Beyer, Peacock to suggest a suitable Garrett for the NIMT, and they were then asked to quote for engines with either four or six cylinders. But the three six-cylinder engines were supplied against their own better judgement. The finger of the London and North Eastern three-cylinder enthusiasts (i.e. Lynde) was evident in this unwise decision.

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 Company of the United Kingdom. These engines had three cylinders (16.5-by-24-inch or 419-by-610-millimetre) 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 unit's frame. Unlike a Union Garratt, however, the rear water tank was still mounted on the rear engine unit.