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The Novice shows his Utmost Inexperience

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Old 01-14-2007, 12:03 AM
Join Date: Apr 2006
Location: St. Paul, MN
Posts: 292
Blog Entries: 13
Default The Novice shows his Utmost Inexperience

Alan Bates, Kenny Howe et al, please respond!

Please take the following with a grain of salt, given that I am by no means an engineer nor do I really know the first thing about the workings of steam engines. Bear this in mind with the following questions:

I was trying to diagram an engine cylinder tonight. I had a piston, two inlet valves and two exhaust valves on either side of the piston. The piston I have drawn in relation to the crank connected to the axle/shaft, as if looking at the starboard engine from the port side. Thus, when the crank is at 0 degrees, the piston is at the aft end of the cylinder, and when the crank is at 90 degrees, the pston is at the center of the cylinder moving forward (away from the shaft). I realize there are probably more technical terms for what I've just said, but again, my ignorance precedes me.

Based on this, I had my diagram as follows:

crank 0 degrees - aft exhaust valve open - inlet valves closed
crank 90 degrees - exhaust valves closed - aft inlet valve open
crank 180 degrees - forward exhaust valve open - inlet valves closed
crank 270 degrees - exhaust valves close - forward inlet valve open

If I've made a grave mistake in this part, please don't hesitate to say so, as I've based my next questions on these previous 4 assumptions.

Here are my questions, assuming the diagram above is correct:

1. At 0 and 180 degrees, a vacuum is formed on one side of the piston, whereas at 90 and 270 degrees, fluid is compressed on one side of the piston. I understand that in a car, this is overcome with a flywheel. However, on a steamboat, is this achieved with the great inertia of the sternwheel? Or is this assuaged by the second engine and its inlet/exhaust?

2. If the engine discussed here is using a slide valve, rather than the type of valves on the DQ or BoL, then is the timing I've been working with correct? i.e., that the inlet slide valve is offset from the piston by 90 degrees and that the exhaust slide valve is directly with the piston?

I ask these questions because I do not understand linkage systems, poppet valves, eccentrics, the entire concept of cutoff, and the like. Any help is greatly appreciated! I hope that in order to understand the basics, I will not have to pursue a mechanical engineering degree!
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