Live Steam 
Duplex Twin Cylinder "Mill" Model Steam Engine 
Fully Machined Kit in Brass, Bronze & Steel


The horizontal twin cylinder Duplex "mill" engine is two single cylinder mill engines connected via a large flywheel on a steel plate and optionally inlet/outlet manifolds. As such it is still relatively simple and retains the basic mechanics of engines which powered mills and workshops and which needed the extra power provided by a twin cylinder engine.


NOTE: Pictures are of the finished, assembled and painted model, this listing is for the kit of parts, see picture.


This mill engine layout has two double acting cylinders, eccentric driven slide valves and the large brass flywheel offers smooth running and is capable of powering a range of accessories, in a variety of roles. The engine also includes twin split bronze pedestal bearings for each of the two crank shafts, two cast bases and a steel base plate.


The cranks for each cylinder are offset by 90° which means the engine will self-start in any position.


The engine will run in reverse by applying the steam (or air) input to the outlet ports. Ou
Reversing/Throttle Valve (optional extra) will control the direction and speed of the engine in either direction.


The kit consists of precision produced parts each carefully made and checked to ensure ease of assembly and reliability in service.


The cylinder assembly and piston are manufactured from brass and the piston shafts, connecting rods and valves from stainless steel so are not susceptible to corrosion. The piston shafts passes through adjustable glands and the steam inlet can be on the top or bottom of the chests.


Detail Specification:

- Type: Horizontal Slide
- Bore: 14mm
- Stroke: 18mm
- Flywheel Diameter: 70mm
- Valve type: Piston
- Height (excluding optional manifold): 75mm
- Length: 150mm
- Width: 130 mm
- Weight: 2.2Kg
- Connections: 1/4" x 40 tpi ME


The kit consists of a set of fully machined parts that can easily be assembled using simple tools such as a screw driver, small spanner, allen keys, pliers and metal file. The parts are mainly unfinished metal and will also require painting, polishing, filing, etc. to achieve the appearance shown in the pictures.


NOTE: The kit is supplied with socket or hex head set screws (as per the pictures), although some screws for ease of installation, have to be socket head screws. Some screws as provided may need to the cut or filed to length to complete the model, contact us if this will cause a problem.


The pictures show the optional Manifold set which combines two inlet or outlet ports together into a single port.


When assembled the engine is fully working and can be run using steam or simply using compressed air e.g. from hand or foot pumps.


To power the engine with live steam, connect it to one of our Model Steam Boilers.


NOTE: The model steam engines and boilers are NOT children’s toys and should not be assembled or operated by children unless under close supervision of an adult.

Name Size Action
Tandem Twin Cylinder Model Steam Engine Assembly Drawing 849.08KB Download
Tandem Twin Cylinder Model Steam Engine Assembly Instructions 1.69MB Download

Duplex Mill Twin Cylinder Engine Kit

  • Product Code:HTTA
  • Availability:Out Of Stock
  • £354.00


Available Options


Related Products

Pulley Wheel

Pulley Wheel

The pulley wheel is designed as a simple add-on to all our engines and can be used to drive all kind..

£10.00

Steam Reversing Throttle Valve

Steam Reversing Throttle Valve

The valve will allow our engines  to be run in forward and reverse and their speed controlled b..

£49.00

Small Adjustable Displacement Lubricator for Live Steam Model Engines

Small Adjustable Displacement Lubricator for Live Steam Model Engines

Small solid brass adjustable displacement lubricator/oiler - should be installed in the steam pipe f..

£42.00

Large Adjustable Displacement Lubricator for Live Steam Model Engines

Large Adjustable Displacement Lubricator for Live Steam Model Engines

The Large Adjustable Displacement Lubricator/oiler is made mainly of solid brass and should be insta..

£46.00

Medium Adjustable Displacement Lubricator for Live Steam Model Engines

Medium Adjustable Displacement Lubricator for Live Steam Model Engines

The Medium Adjustable Displacement Lubricator/oiler is made mainly of solid brass and should be inst..

£45.00

Tags: Live Steam, Model Steam Engine, Fully Machined Kit, Twin Cylinder, Duplex Mill Engine