4-6-2+2-6-4

File:SAR Class GF (4-6-2+2-6-4).jpg

South African Railways Class GF, the first 4-6-2+2-6-4 Double Pacific

In the Whyte notation for the classification of steam locomotives by wheel arrangement, a 4-6-2+2-6-4 is a Garratt or Union Garratt articulated locomotive using a pair of 4-6-2 engine units back to back, with the boiler and cab suspended between them. The 4-6-2 wheel arrangement has four leading wheels on two axles, usually in a leading bogie, six powered and coupled driving wheels on three axles, and two trailing wheels on one axle, usually in a trailing truck. Since the 4-6-2 type is known as a Pacific, the corresponding Garratt type is usually known as a Double Pacific.

Other equivalent classifications are:

• UIC classification: 2C1+1C2 (also known as German and Italian classifications)
• French classification: 231+132
• Turkish classification: 36+36
• Swiss classification: 3/6+3/6 up to the early 1920s, later 6/12

Overview

Garratt

The Double Pacific type was fairly common for Garratt locomotives, especially those intended for faster passenger service. The first of the type was the Class GF, built by Hanomag for the South African Railways in 1927. The first to be built by Beyer, Peacock and Company, the owner of the Garratt patent, was the G class for the New Zealand Railways Department in 1928. Beyer, Peacock also built the last Double Pacific in 1943, for the Nigerian Railways.

Union Garratt

The South African Railways also operated a Double Pacific version of the Union Garratt articulated locomotive. The Union Garratt was a hybrid locomotive, partly Modified Fairlie and partly Garratt. The front end was of a typical Garratt arrangement, with a water tank mounted on the front engine unit’s frame, while the rear end was constructed in the Modified Fairlie fashion, with the coal bunker mounted on a rigid extension of the locomotive’s main frame and with the pivoting rear engine unit positioned beneath the coal bunker. It had an additional large underbelly water tank under the boiler. The main frame therefore carried the smokebox, boiler, firebox, cab, coal bunker, as well as the underbelly water tank. As a result the Union Garratts, like the Modified Fairlies, were prone to metal fatigue and cracking of the frames, in the case of the Union Garratts particularly at the rear, brought about by the long frame overhang laden with the coal bunker.

4-6-2+2-6-4 Garratt production list – All manufacturers

Gauge	Railway	Class	Works no.	Units	Year	Builder
Template:TrackGauge	Ferrocarril Dorada, Colombia		6843-6844	2	1938	Beyer, Peacock
Template:TrackGauge	Midland of Buenos Aires, Argentina		6570-6571	2	1929	Beyer, Peacock
Template:TrackGauge	Leopoldina Railway, Brazil		6572-6573	2	1929	Beyer, Peacock
Template:TrackGauge	Leopoldina Railway, Brazil		6845-6850	6	1937	Beyer, Peacock
Template:TrackGauge	Leopoldina Railway, Brazil		7026-7033	8	1943	Beyer, Peacock
Template:TrackGauge	Vicoa Ferrea do Rio Grande do Sul, Brazil		22047-22056	10	1931	Henschel
Template:TrackGauge	New Zealand Government Railways	G	6484-6486	3	1928	Beyer, Peacock
Template:TrackGauge	Nigerian Railways		6781-6784	4	1935	Beyer, Peacock
Template:TrackGauge	Nigerian Railways		6796-6797	2	1936	Beyer, Peacock
Template:TrackGauge	Nigerian Railways		6861-6866	6	1937	Beyer, Peacock
Template:TrackGauge	Nigerian Railways		6927-6930	4	1939	Beyer, Peacock
Template:TrackGauge	Nigerian Railways		7051-7056	6	1943	Beyer, Peacock
Template:TrackGauge	South African Railways	GF	10512-10548	37	1927	Hanomag
Template:TrackGauge	South African Railways	GF	21053-21070	18	1928	Henschel
Template:TrackGauge	South African Railways	GF	5748-5757	10	1928	Maffei
Template:TrackGauge	PLM, Algeria	231-132.AT	2678	1	1932	Franco-Belge, France
Template:TrackGauge	C.F.Algeria	231-132.BT	2697-2708	12	1936	Franco-Belge, France
Template:TrackGauge	C.F.Algeria	231-132.BT	2711-2714	4	1937	Franco-Belge, France
Template:TrackGauge	C.F.Algeria	231-132.BT	2725-2730	6	1939	Franco-Belge, France
Template:TrackGauge	C.F.Algeria	231-132.BT	2741-2747	7	1940	Franco-Belge, France
Template:TrackGauge	Central of Aragon, Spain		191-196	6	1931	Euskalduna, Bilbao

Usage

Mozambique

In the late 1960s four South African Class GF 4-6-2+2-6-4 Garratt locomotives were sold to the Caminhos de Ferro de Moçambique (CFM), where they became the Series 911.

New Zealand

NZR G class of 1928

Three six-cylinder G class Garratt locomotives were built for the New Zealand Railways Department (NZR) by Beyer, Peacock and Company in 1928. They were the only six-cylinder simplex Garratts ever used in New Zealand and used Walschaerts valve gear to operate the outside cylinders, while Gresley conjugated valve gear operated the inner third cylinders. The locomotive was equipped with a mechanical stoker and was of an unusual design, with the coal bunker mounted on an extension to the main frame instead of being mounted as a coal-and-water bunker on the rear engine unit’s frame, as was the usual practice on Garratt locomotives.

The Garratts were acquired in response to traffic growth over the heavy grades of the North Island Main Trunk and to eliminate the use of banking locomotives on steep gradients. However, since they proved to be unsuccessful and problem-ridden in service, they were withdrawn in 1937 and rebuilt to six three-cylinder 4-6-2 Pacific locomotives by the NZR’s Hillside Workshops.

South Africa

In 1927 the South African Railways (SAR) placed thirty-seven Class GF Garratt locomotives in service. They were the first of the 4-6-2+2-6-4 type and were built by Hannoversche Maschinenbau AG (Hanomag) in Germany. The locomotive specifications were prepared by Colonel F.C. Collins, Chief Mechanical Engineer of the SAR from 1922 to 1929, who designed it as a mixed traffic locomotive for use on branch lines and secondary main lines throughout the country.

File:Class GH (4-6-2+2-6-4).jpg

SAR Class GH Union Garratt, circa 1930

A second order was placed with Henschel & Son for eighteen locomotives that were delivered in 1928. These were followed by a third order, placed with Maffei in 1928, for a final batch of ten locomotives that were delivered in that same year. They were superheated, had bar frames and used Walschaerts valve gear. Its good turn of speed and reasonably high tractive effort made the Class GF Double Pacific a good utility locomotive and, with sixty-five locomotives, the class was the most numerous Garratt type in SAR service until the arrival of the Class GMA and Class GMAM in 1954.

In 1928 the SAR placed two Class GH passenger train versions of its Class U Union Garratt in service, designed and built by Maffei, to work the named fast passenger trains of the era, the Union Express and Union Limited, forerunners of the Blue Train. They were superheated and had Walschaerts valve gear, bar frames and mechanical stokers. They made several trips working the two "Union" trains out of Cape Town, but they were not as successful as had been hoped and they were soon taken off that duty. Their mechanical stokers also proved to be troublesome and were eventually removed. Both remained in service until 1958.

Spain

File:RN462-040XJPVL.jpg

Spanish Serie 462-0400

Six Garratt locomotives of this wheel arrangement were used on the 5 ft 6 in (1,676 mm) Ferrocarril Central de Aragón (FCA) in Spain, built by Euskalduna in 1931. They worked the heaviest passenger trains on the steepest gradients from Valencia to Zaragoza.

After the FCA was integrated into RENFE (Red Nacional de los Ferrocarriles Españoles) in 1941, the locomotives were converted to oil-burners and worked in the Tarragona-Valencia section on the line between Barcelona and Seville, until they were replaced by diesel traction in 1967 and retired.