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The NZR Ab Class Locomotive  
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The NZR Ab Class locomotive was a remarkable piece of engineering in its time. It first saw the light of day in 1915 and achieved the exceptional feat of generating 1 drawbar horsepower per 100lbs of Locomotive. This page is my tribute to a wonderful piece of New Zealand's Industrial History.

Ab795, image from "Classic Steam Locomotives of New Zealand" by Eric Heath and Bob Stott
Reproduced with the kind permission of Eric Heath
© 2012 Eric Heath

Ab778, Kingston, New Zealand, October 2007

Design and Production

In Service

Ab699, Pleasant Point

Ab699, Pleasant Point


Modified Tenders


The Wab

Wab Conversions


Exhaust Steam Injectors

The Exhaust Steam Injector on Ab699 at Pleasant Point.
This is below the cab on the fireman's side; the locomotive is facing to the left.

Left: The Exhaust Steam Injector control at the fireman's side of the cab. The black vertical bar has a handle which lifts up and then rotates to turn on the water supply to the ESI. (corrected thanks to Paul Woods, previously I said steam supply). The steam supply is probably the wheel to the right of the water supply lever.


Right: Fireman's side, looking forward. According to Paul (who is familiar with the system on J and Ja locomotives) the vertical handle is the steam shut-off valve for the Sellars live steam injector, and the valve (wheel below the handle) is the water valve for the Sellars.

Click on either image for a better view

Was the Ab a World beater?

Author's notes



Ab699, complete with Exhaust Steam Injector, at speed on the Pleasant Point Railway

A special thanks to these contributors:

  • Eric Heath - Artwork of Ab795
  • Paul Woods - notes on operations and corrections to control labels on photos
  • Tim Marshal - additional listings of Locomotives with and without Exhaust Steam Injectors


  • Classic Steam Locomotives of New Zealand, by Eric Heath and Bob Stott, Grantham House Publishing, 1993 ISBN 0 86934 036 1
  • Steel Roads of New Zealand, edited by Gordon Troup, A.H. & A.W. Reed, 1974, ISBN 0 589 00735 1
  • When Steam was King, W.W. Stewart, A.H. & A.W. Reed,1970, ISBN 0 589 00382 8
  • The NZR Steam Locomotive, Sean Millar, New Zealand Railway and Locomotive Society, Inc, 2011, ISBN 978-0-908573-89-9
  • New Zealand Railfan, December 2004, Quarterly Magazine produced by Triple M Publications, P O Box 44-444, Mosgiel, Otago 9053, New Zealand
  • New Zealand Model Railway Journal, various dates, Quarterly Publication, New Zealand Model Railway Guild, http://nzmrg.org.nz
  • Steam, Steel, and Splendour, David Leitch, Harper Collins 1994
  • Farewell to Steam, Tony Hurst, Harper Collins ISBN 1-86950-187-X
  • The Spirit of Steam, Roy Sinclair, Whitcoulls, 1975, ISBN 0851532683
  • South Island Main Trunk, Geoffrey B Churchman and Tony Hurst, IPL Books, ISBN 0-908876-78-5
  • The Country Commuter, published by the Canterbury Railway Society
  • Chris Bradley's photos on Flikr, http://www.flickr.com/photos/tutaenui/ provided conclusive information on ten Ab's and their ESI status. An excellent collection of 1960's NZR photographs.
  • The International Steam Pages, http://www.internationalsteam.co.uk/tales/lythgoe00.htm - photo essays from around the world, another excellent set of photographs and captions. This time by Wilson Lythgoe


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  (c) Copyright Brian Greenwood 2013