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Model Steam Engine Plans

 Beam Engines

Stuart beam EngineBeam engines come basically in two sorts, the half beam and walking beam engine, with sizes ranging from colossal, weighing hundreds of tons in full size, to the model engineers version which can be around the size of your hand.

They started off initially as rocking beam engines to provide pumping facilities for mines, using atmospheric pressure on a large piston with a partial vacuum on the other side of the piston to drive the piston along its stroke to raise the water, with the weight of the pump 'buckets' below ground providing the downwards part of the pumping action.

The one above is a later version (the generally known walking beam engine) using higher steam pressure, as boiler pressure was gradually raised owing to the better production methods and boiler materials. This one also has a flywheel allowing roatation motion to be used, whereas the very early originals mostly had a rocking beam with no flywheel, used simply as a push-pull engine for the pumping action.

They would have low pressure steam entering the cylinder from below the piston with a rocking beam engine as the weight of the linkage falling down the pumping shaft raised the piston in the cylinder and draws in the steam. Once at the top of its stroke with the cylinder filled with low pressure steam there would be cold water sprayed into the steam which quickly condensed causing a partial vacuum inside the cylinder below the piston. Air pressure above the piston then forced the piston down its stroke causing the pumping action to lift the water from the mine shaft.

These early engines had the top of the piston rod fixed to the beam so that the piston had to rock slightly in the cylinder, meaning the piston seal was rudimentary, much like a bicyle pump is at present, using a rubber seal with water above it to keep the air out as the vacuum was created.

They were not very efficient or powerful owing to air pressure not being much higher than the partial vacuum created below the piston seal, so needed very large diametered pistons to achieve much work. But the larger the diameter the greater the difficulty with sudden cooling of the steam, meaning they were very slow acting.

half beam engineThis beam linkage was eventually modified using what is known as parallel motion, the walking beam, to keep the con-rod acting in one plane, and from this era boiler pressures were increasing so that was the beginning of the industrial revolution for the whole world when flywheels were incorporated for factory and other industrial usage.

Half beam engines like this one on the left were a modification to full beam engines because of space saving needs in that the beam is supported at one end above the cylinder with a pivoting column at the other end and the drive is taken from the beam to a flywheel at around one quarter to one third the way along the beam from the cylinder.

In use the beam itself pivots on the arms running from the top of the triangular support above the cylinder giving a strange, but very pleasing motion to the whole engine.


Available Plans
Gerry's Beam Engine Plans                       FREE
Gerry's Beam Engine Instructions             FREE
1932 Model Engineer Beam Engine          FREE

Walking Beam Engine                             Medium easy build                                
Vertical valve design steam engine          Medium easy build
Wood engine                                           Simple build
Twin cylinder engine       french              Complicated 
GEO2 Boiler design                                Easy build      
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