Topic starter
14/01/2007 5:03 am
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!
14/01/2007 10:27 am
You have the right idea, Jon, but there is a lot more to valve gear events. Consider one end of an engine. If you were to close the exhaust and open the admission suddenly at the end of a stroke the steam would literally hammer that piston. Actually, the exhaust valve is closed before the end of the stroke to compress the steam left in the cylinder. The admission valve starts to open a very short time before the end of the stroke and this is called release. This period is called compression. When the piston reaches the end of its stroke the admission valve is opened to push the piston away.
In order to save steam the admission valve is closed before the end of the stroke and the expansion of the steam continues to drive the piston. This event is called cut-off. To sum up, four events occur in each revolution of the crank: admission, cut-off, compression and release in that order.
It took a long time and a lot of invention for this to arrive and many men worked to make it happen. The various valve gears are named for their inventors or the plants where they developed. Today you can watch these gears operate on the boats named:
American Queen - Nordberg
Belle of Louisville - Rees
Chautauqua Belle - Stephenson
Delta Queen - Cross, or California
Graceful Ghost - Stephenson
Julia Belle Swain - Gillett & Eaton
Mississippi Queen - McConnell, or Marietta (I think)
Natchez - Walschaert
and you can see them standing still as follows:
Lone Star - Cross, or California
W. P. Snyder Jr. - Rees
Wm. M. Black - McConnell, or Marietta
and I do not know what is on the George M. Verity
14/01/2007 2:40 pm
Jon,
you should buy The Western Rivers Engineroom Cyclopoedium from the Howard Steamboat Museum. It will answer most of your questions.
15/01/2007 2:21 pm
Jon - I can send you the valve motion plots I made on the "Belle of Louisville" the past couple of years if you like. Tell me your mailing address (electronic or USPS, whichever you like).
15/01/2007 4:04 pm
Yep, the MISSISSIPPI QUEEN has Marietta valve gear/cut off. The same set up that was on the OMAR, towboat JOHN W. HUBBARD, CHARLES T. CAMPBELL, et. al. The VERITY, along with her sister ships, has/had NORDBERG machinery.