Wednesday, November 16, 2016

Triple-Action Steam Engine

John Abbott posted
Tad Cuper That crank for Steam or Diesel?
When I saw Tad's comment, I wondered how such a long crank could be for a steam engine. But I had noticed the tool stand looked rather old fashioned for a large diesel engine. Also, the stroke seems to be rather large for a "short" diesel engine. The next day I came across the following video that illustrates why this crank may be for a steam engine. (Fortunately, I was able to find the above picture the next day.) This Texas Battleship's 28,000 hp triple-action steam engine has four pistons because two pistons are used to handle the low pressure steam rather than have one cylinder with a really huge bore. The crankshaft also has three eccentricities to drive the valves. To summarize the video: at full throttle, steam enters the high pressure 39" cylinder at the boiler pressure of 274 lb/sq-in and over 450-degrees Fahrenheit. Steam is used to push each piston up as well as down. The steam pressure is down to 120 when it enters the 63" intermediate pressure cylinder. The steam flow is down to 45 when it is split and enters the two 83" low pressure cylinders. The steam enters the condenser at 15.

A couple of videos of the biggest operating triple-actuin steam engine at Kempton: general tour and using a small steam engine to position the high pressure piston of the big engine for starting. One of the comments said these water pump steam engines are similar to the one used on the RMS Titantic and are about 1008 hp. Note that passenger steam locomotives at their apex of their development were over 6000 hp. So bigger is not necessarily better. Horsepower is a function of speed as well as size. The brief view of the water pumps in the basement indicate they are also reciprocating devices. So why bother with a crankshaft to introduce rotary motion between reciprocating steam pistons and the water pumps? I don't see a big flywheel. On further reflection, the crank keeps the pistons "in phase." That is, it makes sure the next piston is properly positioned to receive steam when the previous piston is exhausting steam.

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