South African Class NG G16A 2-6-2+2-6-2

South African Class NG G16A 2-6-2+2-6-2

The Red Dragon, NG G16A no. 141 at Port Shepstone, May 1990
Type and origin
Power type Steam
Designer Hannoversche Maschinenbau AG
South African Railways
Builder Beyer, Peacock and Company (no. 141)
Hunslet-Taylor (no. 155)
Serial number Beyer, Peacock 7866 (1958) [1]
Hunslet-Taylor 3900 (1968) [2]
Model Class NG G16
Build date 1937-1968
Total produced 34
Rebuilder Alfred County Railway
Rebuild date 1989-1990
Number rebuilt 2
Specifications
Configuration 2-6-2+2-6-2 "Double Prairie" Garratt
Gauge 2 ft (610 mm) narrow gauge
Leading wheel
diameter		 21 in (533 mm)
Driver diameter 33 in (838 mm)
Trailing wheel
diameter		 21 in (533 mm)
Minimum curve 160 ft (48.768 m)
Wheelbase Total: 43 ft 3 in (13.183 m)
Engines:
6 ft 3 in (1.905 m) coupled
13 ft 10.5 in (4.229 m) total
Length 48 ft 3.25 in (14.713 m)
Height 10 ft 4 in (3.150 m)
Frame Bar frame, 23 ft 9 in (7.239 m) between pivot centres [3]
Axle load 7 t (6.9 long tons)
Weight on drivers 39.76 t (39.1 long tons)
Locomotive weight 60.25 t (59.3 long tons)
Fuel type Coal
Fuel capacity 3.85 t (3.8 long tons)
Water capacity 9,865 l (2,170 imp gal)
Boiler 4 ft 7.75 in (1.416 m) inside diameter
9 ft 3.625 in (2.835 m) inside length
5 ft 5 in (1.651 m) pitch
Boiler pressure 180 psi (1,240 kPa)
Firegrate area 1,784 m2 (19,200 sq ft)
Heating surface:
– Tubes		 Small tubes:
152 tubes 44.5 mm (1.75 in) diameter
38.5 mm (1.52 in) bore
60.24 m2 (648.4 sq ft)
Large tubes:
15 tubes 140 mm (5.5 in) diameter
130 mm (5.1 in) bore
18.7 m2 (201 sq ft)
Total surface 78.94 m2 (849.7 sq ft)
– Firebox 6.97 m2 (75.0 sq ft)
– Total 85.9 m2 (925 sq ft)
Superheater area 15 elements, 14.9 m2 (160 sq ft)
38 mm (1.5 in) diameter
31 mm (1.2 in) bore
Cylinders Four
Cylinder size 12 in (305 mm) bore
16 in (406 mm) stroke
Valve gear Walschaerts
Valve type 140 mm (5.5 in) diameter
Valve travel 90 mm (3.5 in)
Valve lap 22.22 mm (0.875 in) steam lap
1 mm (0.039 in) exhaust lap
Valve lead 3.5 mm (0.14 in)
Performance figures
Tractive effort 95 kN (21,000 lbf) at 75% boiler pressure & 25% adhesion [4]
Career
Operator(s) Alfred County Railway
Class Class NG G16A
Number in class 2
Number(s) 141, 155
Nicknames Red Dragon
Delivered 1989-1990
First run 1989

The South African Class NG G16A 2-6-2+2-6-2 of 1989 is a South African steam locomotive from the South African Railways era.

Between 1937 and 1968 the South African Railways placed thirty-four Class NG G16 2-6-2+2-6-2 Garratt articulated steam locomotives in service. In 1989 and 1990 two of these locomotives were rebuilt to Class NG G16A by the Alfred County Railway.[4][5]

Manufacturers

Altogether thirty-four Class NG G16 2-6-2+2-6-2 locomotives were built for the South African Railways (SAR) between 1937 and 1968. Four were delivered by Société Anonyme John Cockerill of Seraing in Belgium in 1937, twenty-two by Beyer, Peacock and Company between 1939 and 1958, and the last eight by Hunslet-Taylor in Germiston, Transvaal in 1967 and 1968.[5]

Alfred County Railway

When the four narrow gauge branchline systems in Natal were closed down by the SAR, the Weenen and Mid Illovo lines were torn up, but the Harding line was privatised in 1988 as the Alfred County Railway (ACR), operating out of Port Shepstone. The ACR was also known as the "Banana Express" from the tourism part of its operation.[6][7]

Class NG G16A rebuilding

As part of the ACR’s strategy to keep the narrow gauge railway competitive, two of its Class NG G16 Garratt locomotives were rebuilt using technology similar to that used by mechanical engineer David Wardale in the creation of the Class 26 "Red Devil" in 1980, based on developments pioneered by Argentinian engineer L.D. Porta. The Class NG G16 rebuilding incorporated a gas producing combustion system (GPCS), Lempor exhausts, an improved spark arrester, lightweight multi-ring articulated piston valves, improved valve events and improved mechanical lubrication.[4][8]

The rebuilding was done by mechanical engineer Phil Girdlestone, who was employed as Chief Mechanical Engineer of the ACR primarily for this purpose. The work was carried out at Port Shepstone, and the first locomotive to undergo the treatment was the Beyer, Peacock-built number 141 in 1989.[4]

The rebuilding was similar in scope to that of the Red Devil, although not as extensive. Like the Class 26, number 141 was also painted red and was consequently soon nicknamed the "Red Dragon". Dragon emblems were later mounted on the cab sides and bunker ends.[4]

The second locomotive, the Hunslet-Taylor-built number 155, was rebuilt in 1990 but it retained its traditional ex SAR black livery. Both modified locomotives were reclassified to Class NG G16A.[4]

Gas producing combustion system

Secondary air inlets with swirl inducers and a spark arresting plate

The GPCS is a single-stage gas producer that achieves an improved combustion and steaming rate, reduces the emission of wasteful black smoke and overcomes the problem of clinkering. The most serious waste of fuel in a conventional steam locomotive is the loss of unburned coal particles from the fuel bed through the exhaust because of the rapid flow of air through the grate.[9][10]

The GPCS relies on the gasification of coal on a low temperature firebed so that the gases are then fully burnt above the firebed. To achieve this, the amount of air being drawn up through the firebed is minimised while the main sources of air required for combustion is through secondary air inlets located in the firebox sides and through the vertically sliding firedoor. The air inlets contain swirl inducers to spread the incoming air inside the firebox.[4][5][8][9]

With the GPCS the coal is therefore heated to drive off the volatile components which are then burned in the secondary air admitted above the grate. The result is improved combustion, thereby minimising black smoke which is evidence of incomplete combustion and unburnt coal particles being ejected through the exhaust. Note the clear exhausts in the picture in the gallery below, of numbers 141 and 155 double-heading on the climb from Bongwana to Nqabeni.[4][9]

Lempor exhaust

One of the most obvious externally visible differences between the original and the rebuilt locomotives is the megaphone shaped Lempor chimney, which contains a cylindrical mixing chamber and a wide angled diffuser. The object of the latter is to convert the kinetic energy of the combustion gas and steam mixture to a pressure as close to atmospheric as possible. This requires that the outlet area should be as large as possible since that would allow the largest possible blast nozzle area and therefore the lowest back pressure.[4]

Ejector pump efficiency depends on the length-to-diameter ratio of the exhaust chimney. Although less obvious, both Wardale GPCS locomotives, Class 19D 2644 and Class 26 3450, have exactly this shape of chimney, but because of height constraints in large locomotives their chimneys had to be doubled or even tripled to achieve the correct proportions, hence the double exhausts of the two Wardale locomotives. Narrow gauge locomotives like the Class NG G16, on the other hand, have plenty of height available for the exhaust, so a single long chimney was achievable.[4]

Other visible differences are larger mechanical lubricators and external drive from the valve spindle, a vacuum ejector exhaust muffler just in front of the safety valves, pipes conveying exhaust and ejector steam to the ashpan for mixing with the primary air, the secondary air inlets in the firebox sides with spark arresting plates outside them, and the snifting and bypass valves that were removed and blanked off since the modified locomotive drifted in mid gear with steam supplied from the drifting valve.[4]

Performance

In comparative testing, number 141 achieved a fuel saving of 25% compared to a standard Class NG G16 Garratt, a performance that was easily maintained in regular service. Power outputs of over 700 indicated horsepower was achieved and the locomotive was probably capable of achieving a maximum of 800 indicated horsepower, some 25% more than the Class 91-000 narrow gauge diesel-electric locomotive.[4]

The improvement in performance and economy of the locomotive was brought about by the higher grate limit by means of the GPCS and better flow past the improved valves, valve motion and exhaust. Other basic elements of the locomotive remained more or less the same.[4]

The cost of the work paid off financially within twelve months and led to a proposal to develop a Class NG G17. That, however, never realised since the line’s farming produce traffic was gradually lost to road transport on the improving road network, a decline that eventually led to the ACR’s demise.[8][11][12]

Sides illustrated

The main picture and a following photograph offer views of both sides of the Class NG G16A locomotive.

See also

References

  1. ↑ Hamilton, Gavin N., The Garratt Locomotive - Garratt Locomotives produced by Beyer, Peacock, retrieved 10 November 2012
  2. ↑ Hamilton, Gavin N., The Garratt Locomotive - Garratt Locomotives from Other Builders, retrieved 10 November 2012
  3. ↑ South African Railways and Harbours Locomotive Diagram Book, 2’0” & 3’6” Gauge Steam Locomotives, 15 August 1941, as amended
  4. ↑ 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 Information supplied by Phil Girdlestone
  5. ↑ 5.0 5.1 5.2 Paxton, Leith; Bourne, David (1985). Locomotives of the South African Railways (1st ed.). Cape Town: Struik. pp. 10–11, 78–79, 107, 109–110. ISBN 0869772112.
  6. ↑ Durrant, A E (1989). Twilight of South African Steam (1st ed.). Newton Abbott, London: David & Charles. pp. 126–127. ISBN 0715386387.
  7. ↑ Ash, Paul (2005). Living Steam (Lambert, Anthony – editor) (1st ed.) London, Cape Town, Sydney, Auckland: New Holland Publishers. pp. 120-123. ISBN 1-84330-872-X
  8. ↑ 8.0 8.1 8.2 "Alfred County Railway 2-6-2+2-6-2 NG G16A Garratts 141 & 155". martynbane.co.uk. Retrieved 2009-07-10.
  9. ↑ 9.0 9.1 9.2 Gas Producer Combustion System (GPCS)
  10. ↑ South Africa's 'Red Devil'
  11. ↑ "The Ultimate Steam Page – P. Girdlestone". trainweb.org. Retrieved 2009-07-10.
  12. ↑ Middleton, John N. (2002). Railways of Southern Africa Locomotive Guide - 2002 (as amended by Combined Amendment List 4, January 2009) (2nd, Dec 2002 ed.). Herts, England: Beyer-Garratt Publications. pp. 32–33.

External links

External video
Alfred County Railway NGG16A Garratt November 1996 Follow the Banana Express from the coast at Port Shepstone up the hill to Paddock, hauled by NG G16A 155. On the return trip, 155 picks up 300t of timber in addition to the passenger cars. (12 minutes 22)