Frequently Asked Questions

Replacement Boiler FAQ

Can we use our existing auxiliary appliances? e.g. safety valves, fire-door, whistle, injectors, turbo-generator, etc.

  1. Yes, most existing appliances work with the new boiler, provided they are in good working order and meet required certifications for safety, or we can supply new equipment.
  2. The feed pump supplied with the boiler will provide easier control of the boiler water level compared with injectors.
  3. A new throttle/regulator is supplied with the boiler where required.

How much will a Mackwell boiler cost?

Similar pricing to a replacement boiler of conventional design, price includes steam driven circulating pumps and some auxiliary components.

What fuel can we use?

  1. Any solid biofuel (preferably below 50% moisture content)
    • Cord firewood
    • Wet or dry hog fuel
    • Wood chip
    • Pellet
    • Biocoal
    • Bagasse
    • Rape cake
  2. All boilers are hand fired with a mechanical firing option.

Can we burn coal?


What boiler water treatment is required?

The boiler is designed to work with a simplified version of Porta treatment. This is made up of sodium carbonate and tannin and is supplied by us or can be prepared by the user (full directions and support provided).

Do Mackwell boilers smoke?

No. The unique design of the boiler eliminates smoke emissions by burning solid biofuel in an insulated chamber at temperatures in excess of 900ºC.

Classic locomotives make “clouds of steam,” will this still be the case?

Yes. Emissions of steam from the chimney and cylinder cocks will be unchanged by converting to a Mackwell boiler.

Appearance, clothing, domes etc.

  1. To the untrained eye the locomotives appearance will be unchanged
  2. Original cladding and clothing can be retained with little modification
  3. False domes can be fitted with an identical appearance
  4. Circulating pumps are discretely fitted but have a similar appearance to small Westinghouse air pumps. Feed pumps are similar.

Will there be any changes to external boiler plumbing?

Yes some discrete changes will be required, for example to supply steam to the manifold in the cab. This will be worked out in consultation with the user.

Is the weight the same?

Yes the weight of a custom built Mackwell boiler is identical to the locomotive’s original boiler, however, due to the design the boiler can be supplied up to 50% lighter than the original boiler if it is desired to reduce axle loads or alter the locomotive’s centre of gravity/weight distribution by adding ballast.

Does the boiler emit sparks?

Thanks to the design, Mackwell boilers do not spark. Steam trains during dry summer months are completely safe.

How long does it take to raise steam?

As little as 20 minutes from striking the match depending on the amount of artificial draught available and the skill of the fire lighter.

Will range be affected when using solid biofuel?

Compared to high quality bituminous coal, the volumetric energy of basic wood chip is about 20% by volume or 60% by weight. Densified solid biofuels such as pellets contain about 60% of the energy by volume compared to coal, and 75% of the energy by weight.  In some cases tenders can be modified for additional range when using low cost solid biofuels such as hog fuel or wood chip.

Do we have to clean out the boiler?

Every 100 hrs, small quantities of ash may require removal in the smokebox (we call it an exhaustbox due to the absence of smoke). No tube cleaning is required and the combination of solid biofuel and boiler design eliminates fire cleaning (other than shaking the grate occasionally to remove any nails, stones etc.).

How often does the boiler need to be stripped for inspection?

Inspection is replaced by periodic hydrostatic testing to verify the integrity of the pressure system. Visual inspection of the pressure equipment contained within the smokebox (exhaust box) should be undertaken every 100 hours. The boiler is designed so that it doesn’t require stripping for annual inspection. Daily inspection of the locomotive and boiler systems is still important in accordance with good operating practice. Certification and mandatory inspections will depend on the specific laws that apply in any given jurisdiction, we will work with the operator to understand and navigate these.

Is the Mackwell boiler safer than a conventional boiler?

Yes, much safer due to the very small amount of water under pressure (about 3% of the water contained in a conventional boiler). The boiler’s peer reviewed design contains and safely dissipates the energy of a pressure equipment failure, making the boiler almost as safe as a domestic refrigerator.

Is boiler life the same?

A longer life can be expected due to the reduced stresses, simple design, ease of repairs and the use of Porta treatment to control corrosion and scaling. The pressure system is isolated from the boiler structure and can be repaired independently without replacing the whole boiler.

Will cab layout, controls, fire door etc. be affected?

No, only extremely minor changes are noticeable.

What is the typical delivery time for a custom replacement boiler?

Approx. six to eight months from order placement (depending on shipping)

Payment terms?

50% on order placement, 50% on completion of build prior to shipping.

Will the locomotive’s power remain the same?

The same or more.

Is the funnel (chimney) identical in appearance?

We can use the existing funnel and fit a liner. In some cases, for lower fuel consumption a slightly larger diameter funnel can be fitted of almost identical appearance.

Are the boilers steam tested prior to delivery?

Yes, all boilers are load tested to maximum evaporation (full power) prior to delivery.