5at Train

The 5AT Group - Steaming Ahead with Advanced Technology

Enhancing Performance -- Improving Reliability -- Reducing Costs -- Controlling Emissions

Modernising Options and their Applications

There are a number of modernising options as listed on the Modernisation Options page. This page suggests where each option might or might not be usefully applied.

The "potential applications" column uses five code letters as follows:

  • A - applies to existing locomotives whose external outline must not be changed;
  • B - applies to existing locomotives where some changes to the external outline may be accommodated;
  • C - applies to new-build locomotives whose external outline must not be changed;
  • D - applies to new-build locomotives where some changes to the external outline may be accommodated;
  • E - applies to new build locomotives of new design (e.g. the 5AT)


Modification Benefits Comments Potential Applications
Improved exhaust system Improves steaming, performance and economy by reducing cylinder backpressure, thus increasing cylinder efficiency & reducing specific steam consumption.
Difficult to make significant improvements to the exhaust system without noticeable alteration to the chimney outline. May need adjustments to valve events (e.g. exhaust lead).
Fit Kordina below blast pipe Reduces cylinder back-pressure thus increasing cylinder efficiency & power output, & reducing specific steam consumption.
May be difficult to fit into some existing machines.
Convert (steel) firebox to GPCS operation Reduces unburned fuel carry-over, smoke & spark emissions & clinkering by reducing airflow through firebed and increasing airflow over firebed. Exhaust steam flow into ashpan reduces firebed temperature and thus minimizes clinkering.
Only practicable on steel fireboxes. Airholes in sides of firebox are visible from the outside, thus detracting from original outline.
Increase superheat temperature
Improves fuel consuption and power output by increasing thermal efficiency and reducing Specific Steam Consumption. Reduced fuel consumption reduces carbon emissions

Can be achieved by adjusting the length or type of superheater element, roughening their surfaces or adding fins to increase surface area; also by blanking off some boiler tubes to increase combustion gas flow through the flues; and/or increasing the number of flues and superheater elements. Benfits of this will depend on whether the engine is used on short or long runs.

Install feedwater heater(s)
Reduces fuel and water consumption and/or increases steam production by increasing Specific Volume of steam and reducing Specific Steam Consumption
Feedwater heaters have been notoriously ugly when applied to British locomotives. They have however been elegently incorporated into North American designs and on the Red Devil (and more questionably so on the 5AT). Benfits will depend on whether the engine is used on short or long runs. B,D,E
Cover all hot surfaces with high quality insulation

Reduces fuel and water consumption and/or increases steam production by reducing heat losses and especially by reducing condensation on cylinder walls

Use of high quality insulation has been adopted on a number of locomotives with demonstrable benefits.

Improved valve and piston lubrication Reduce piston and valve ring wear and cracking of lubricant oils by applying them directly onto rubbing surfaces instead of injecting it into the superheated steam flow. This simple expedient can dramatically improve lubrication and reduce wear (and therefore maintenance). Essential when high temperature superheat is adopted.
Multiple narrow "diesel quality" valve and piston rings Reduce fuel and water consumption and thus reduce Specific Steam Consumption by minimising steam leakage. Also reduce ring wear and maintenance costs.
Steam leakage past valve rings is an unseen and usually unknown phenomenon that has been known to waste 20% of a boiler's output (more at low speeds). Good ring design can eliminate this and can dramatically reduce wear rates.
Multiple element piston and valve rod glands Reduce fuel and water consumption and thus reduce Specific Steam Consumption by eliminating steam leakage from glands between overhauls If steam leakage past piston and valve rod glands is eliminated, it will reduce maintenance costs as well as fuel & water consumption.
Modify valve ports and valve heads

Reduce triangular losses by streamlining ports and valve heads; also improve cooling of valve liners, valve heads and valve rings to improve lubrication.

Streamlining of ports and valve heads can be undertaken in association fitting of multiple valve rings (described above).
Saturated steam cooling of valve liners Reduce liner temperature - recommended for very high temperature superheat Cooled valve liners are only warrented where very high temperature superheating is used (upwards of 400oC).
Increase steamchest volume and steam pipe diameter

Reduce pressure drop of admission steam at high steam flow rates thus improving efficiency and Specific Steam Consumption.

Enlarging the steamchest is difficult to implement unobtrusively on existing locomotives. B,D,E
Optimise valve events Improve steam flow into and out of cylinders by adjusting valve motion, lap and/or lead. Detailed evaluation required before changes are implemented. A,B,C,D,E
Optimise clearance volume by modifying pistons and/or cylinder covers Reduce incomplete expansion losses without impeding steam flow, thus raising Specific Steam Consumption, efficiency, etc.
Clearance volume may be able to be reduced by fitting filler plates to cylinder covers and/or piston heads. See "The Brim" - Fig 24 in Porta's Fundamentals of Compounding paper.
Fit roller bearings wherever practicable
Minimise wear, knocking and loss or distortion of valve motion.
Fitting roller bearings to external motion involves changes to external appearance.
Fit Franklin wedges to hornguides
Postpone development of knocking as hornguides wear
Should be considered for new-build projects. Adopted on the 5AT.
Fit Franklin-type buffing mechanism between engine and tender
Reduce buffing shocks between engine and tender; reduce fore-aft rocking from unbalanced reciprocating masses
Should be considered for new-build projects. Adopted on the 5AT. C,D,E intended for main line
Fit air-sanding equipment Reduce risk of slipping and consequent delays, damage etc
Superior to steam sanding, but requires provision of compressed air.
Main line locos only
Adopt mid-gear drifting Maintain steam pressure against admisssion edge valve rings, and prevent smokebox contaminants from entering cylinders. Does not require any physical modification to implement, however snifting valves should be removed or disconnected, as should bypass valves. A,B,C,D,E
Adopt Porta water treatment
Reduces or eliminates corrosion and scale formation; dramatically reduces boiler maintenance costs. Not required on railways that have their own water treatment plants, excapt for itinerant locomotives that move from one railway to another).

Note: It is not recommended that any modifications be carried out that increase an existing locomotive’s tractive effort without proper engineering analysis. Increasing tractive effort is likely to result in forces in the locomotive's motion, frames, drawgear etc. for which they have not been designed. Thus if, for example, any increase in boiler pressure is proposed (to improve thermal efficiency), it may be wise to reduce cylinder diameter such that the original nominal tractive effort is retained.