Steam engines

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Mark F. Jenkins

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Steam engines on mid-1800s vessels fell into two general types:


Low-pressure (condensing) engines: The type found in most ocean-going and coastal vessels. A condensing steam engine's piston is worked in part by atmospheric pressure, as the exhaust steam is cooled and condensed back into water, creating a partial vacuum on one side of the piston; the water is then mostly recirculated back into the boilers. Generally more fuel-efficient and safer than high-pressure engines, but did not produce as much power per weight of engine, and could generally not provide much in the way of reserve power or quick acceleration. Boilers usually did not carry much more pressure than the surrounding atmosphere, so boiler failures were rare and usually very contained.

High-pressure (noncondensing) engines: The type found in most riverboats; more similar to a locomotive engine, where the high-pressure steam is what drives the piston, and then the steam is usually vented off into the atmosphere. Requires a constant supply of fresh water to replace the exhaust, so impractical in salt-water craft, and comparatively fuel-inefficient; but could provide more power for the weight of the engine and was capable of more reserve power and faster acceleration. Because of the high (many atmospheres) pressure in the boilers, boiler failures could be catastrophic and could rapidly spread live steam throughout the vessel.
 

ExNavyPilot

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Good explanation. I know a little about the more modern 1,200 psi steam systems (driving turbine, not piston, engines) that have been used in the US Navy, but didn't know anything about the older systems. I figured the steamboats used high-pressure systems as their boiler explosions were so deadly.
 
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