74 . POLE STEAM-ENGINE. 



cuum, were combined successfully to an extent scarcely 

 ventured on by modern engineers. 



Trevithick's high-pressure condensing whim-engines 

 had been for some years at work in Cornwall, but mine 

 adventurers had not dared to risk the application of 

 high-pressure steam to the large pumping engines, 

 fearing its great power would prove unmanageable, 

 and its rapid movement cause breakage of the pump- 

 rods and valves. 



Two distinct inventions or improvements, each of 

 which was actually followed up in different mines, 

 show themselves in this engine : one being the form of 

 boiler to give with economy and safety high-pressure 

 expansive steam for large engines; the other, the ap- 

 plication of a pole in lieu of a piston, as a more simple 

 engine for working with strong expansive steam, and 

 more easily constructed by inexperienced mechanics, 

 who had none of the slide lathes or planing machines 

 so much used by engine builders of the present day. 



"About 1814 Captain Trevithick erected a large high- 

 pressure steam-puffer pumping engine at the Herland Mine. 

 The pole was about 30 inches in diameter, and 10 or 12 feet 

 stroke. There was a cross-head on the top of the pole, and side 

 rods to a cross-head under the pole-case. The side rods worked 

 in guides. The pole-case was fixed to strong beams immediately 

 over the pump-shaft. The steam was turned on and off by a 

 four- way cock. The pressure was 150 Ibs. to the inch above 

 the atmosphere. The boilers were of wrought iron, cylindrical, 

 about 5 feet 6 inches in diameter and 40 feet long, with an 

 internal tube 3 ft. in diameter. The fire-place was in the tube. 

 The return draught passed through external brick flues." l 



" When a young man, living on a farm at Gurlyn, I was sent 

 to Gwinear to bring home six or seven bullocks. Herland Mine 



1 Recollections of the late Captain Charles Thomas, manager of Dolcoath 

 Mine. 



