Cornish tin mine early type
I really struggled to get this one running, thought I had copied the original pretty well and yet it barely functioned so I read up a bit more history and discovered Newcomen had the same trouble!
Should have copied the Mk2 one!!
Following Newcomen’s 1725 Footsteps
The simplest of mechanical engines –
Expand water into low pressure water vapour (steam) by boiling in some kind of big kettle
Drive air out of working cylinder by filling with this steam
Seal cylinder with piston at the top
Shrink the steam back into water by cooling causing vacuum in cylinder
Atmospheric pressure of about 14.5 psi sucks piston down to the bottom
Let steam in again and piston returns to top (by weights not steam pressure)
And so on…
Just imagine Newcomen’s dream of the power of 14.5 psi acting on a 48 inch diameter piston. You do the maths!
What could be easier?
My engine barely ran and I spent many hours pondering the layout sketches of Newcomen’s engine and in desperation read more history only to discover his first engine barely ran !
1. The power cylinder needed to be hot when the steam was first let in (or through) or it would instantly condense, then when it was full and sealed it needed to cool to condense the steam and produce the vacuum. This thermo-cycling wasn’t going to happen quickly so he added a water squirter to the cylinder which helped to speed things up but cost him quite a loss of vacuum in the process.
2. I hadn’t allowed for incomplete vacuum. In fact probably only achieving about half of that precious 14.5 psi. The power cylinder needed to be far bigger than the piston stroke.
3. Condensing the steam produced water! and the cylinder soon filled necessitating a regular drain out operation. Not shown in original drawings.
4. The power stroke length was unreliable making any kind of automatic valve operation difficult. Also it would have raised problems at the working end where the engine was supposed to be able to pump water or even lift mineworkers up the shaft.
5. Newcomen used water to seal his piston and so did I but some of it got sucked past the piston and added to the unwanted condensate in the bottom (where the steam went in)
6. Operating valves, taps, cocks when everything was stationary was next to impossible to achieve automatically. I later made a fully hand driven version and then understood how boring it would have been for the engine driver, no wonder they later made elaborate mechanisms with ropes and weights.
7. On top of all this Newcomen had to let his kettle boiler cool down when it needed more water. There was no such thing as a boiler pump.
His Mk2 engine incorporated a separate cold vessel strictly as a condenser, this one ran relatively well and should have been the one I copied!
Remember back then in the early 1700’s there were no machine tools, cast iron was the main metal, no lovely steel and boiler leaks were plugged with mud, there was no mechanical way of producing a decent round cylinder bore, they had to use hand tools.
Those pioneers were amazing.
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