Announcement

Collapse
No announcement yet.

Back to Steam--

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • sasquatch
    replied
    Great news Brian , still following here when i get the chance!

    Leave a comment:


  • brian Rupnow
    replied
    AWRIGHT!!! We've-got foreword and reverse working on one cylinder. Hooray Hooray---Happy Dance. What a wrestle!--Spent a very large portion of today (with help from numerous others) getting the valve adjusted. Hope the other side goes a bit easier.
    Last edited by brian Rupnow; 11-15-2017, 07:24 PM.

    Leave a comment:


  • brian Rupnow
    replied
    A short video of the complete Stephensons reversing linkage on my engine.
    https://www.youtube.com/watch?v=84W3HiL-je4

    Leave a comment:


  • brian Rupnow
    replied
    A gentleman on a different forum has shown me the error of my ways. It isindeed correct that the stroke of the steam valve is what determines the "throw" on the eccentric, and is not directly related to the "throw" of the crankshaft. I'm sure that there is some esoteric science that explains why steamchests would be longer or shorter, requiring a greater or lesser "stroke" of the steam valve, but it is a road I don't really want to go down right now. As far as "lap" and "lead" are concerned, I have a glimmer of why this would be so, as it relates to internal combustion engines where the valves don't open and close when the piston is exactly at top or bottom dead center. I have always set my model "steam" engines up with the steam valve positioned exactly in the center of it's travel when the piston is either at top or bottom dead center, and that has always worked for me. I will let you know how that works out with this engine.---Brian

    Leave a comment:


  • Guest's Avatar
    Guest replied
    Originally posted by brian Rupnow View Post
    Here is a short video of me practicing my Canadian Newfie accent and demonstrating the working of my first stage of reversing mechanism.
    https://www.youtube.com/watch?v=d2UiP4gDUKE
    Very nice drill bit holder

    Leave a comment:


  • J Tiers
    replied
    Actually, the throw of the valve eccentric is not really directly related to the crankshaft throw, but clearly directly related to the valve dimensions. The valve has to move the distance required to cover and uncover the steam ports and exhaust port, and the eccentric needs to be able to move it that far.

    Presumably, the dimensions you have used do that, since the engine runs.

    When moved to reverse, the valves should occupy the positions they need to for the piston positions of both cylinders in the new direction. So a piston at half stroke would essentially have the valve position reversed so that steam is admitted to the opposite side of the piston, etc, neglecting any issues of cutoff, etc. If the piston is near one end of the stroke, then the same reversal of sides occurs, with the side that was closing on exhaust being reset to be opening to steam.

    It should not matter which cylinder is being considered, both should be set to the conditions for the opposite rotation when reversed. This should be automatic if the eccentrics are set properly for each direction.

    Leave a comment:


  • brian Rupnow
    replied
    Here is a short video of me practicing my Canadian Newfie accent and demonstrating the working of my first stage of reversing mechanism.
    https://www.youtube.com/watch?v=d2UiP4gDUKE

    Leave a comment:


  • brian Rupnow
    replied
    Thank you gentlemen-My knowledge of steam engine valve setting so far, extends to the eccentric position relative to the crankshaft and the slide valve relative to it's position in the steamchest. The "throw" of the eccentric should be equal to 1/4 of the "throw" on the crankshaft. My crankshaft has a "throw" of 3/8" (which gives a total stroke of 3/4"). The "throw" on my eccentric is .094" which gives the slide valve a total travel of .188" . When the piston is at bottom dead center, the eccentric lobe should be half way thru it's highest and lowest points of travel (that is how you position the eccentric rotationally in respect to the crankshaft. Also, at this time and position, the slide valve should be exactly half way thru it's full travel (3/16") in the steamchest. This method has always worked well for me. The set up for reversing apparently follows exactly the same procedure when setting up with the straight rod directly below the valve rod vertically. When the reversing handle is rotated thru 30 degrees, this brings the offset rod into position directly below the valve rod and hopefully makes the engine run in reverse. I think I've got it, but will only know when I have everything reassembled. I'm a bit unclear what happens at the other cylinder, as the crankshaft is 90 degrees "out of phase" yet is still connected to the same reversing lever.
    Last edited by brian Rupnow; 11-13-2017, 10:59 AM.

    Leave a comment:


  • JCHannum
    replied
    Looking at the engine in the drawing, the valve rod and eccentric rod are in a straight line it that position. Moving the reverse lever to the other position should put the other eccentric rod in the same relationship to the valve rod. If so, all is OK.

    Since you have already set up the engine to run, you have the setting basics correct. The eccentrics should be at 120* separation at BDC. Decide what is forward, and set the engine to run in that direction with one set of eccentrics. The engine should run in reverse with no further adjustment if all is correct by moving the reversing lever.

    You will need a detent or some other means of retaining the lever in the reverse and forward positions to prevent it from vibrating out of position.

    Leave a comment:


  • J Tiers
    replied
    The valves will need some means for adjusting.

    The basic adjustment is the eccentric position, of course. But the slide valve also needs to have the rod length set to place the center of the movement correctly in relation to the valve openings. That is part of setting the "lap" and so forth.

    Some of the details are needed mostly to get the best power out of the engine, which you may not need to do. There is a larger range over which it will "run".

    Since we have seen it running on air, the basics should be covered already.

    Leave a comment:


  • aostling
    replied
    Originally posted by aostling View Post
    I have my father's engineering textbook from the 1930s -- on reciprocating steam engines. Your splendid engine has inspired me to open its pages for the first time in ages.
    The book is Steam Engine Theory & Practice (1934 edition), by William Ripper. Chapter IV is all about the slide valve, and the eccentric which effects the valve operation and timing. There is a simmple formula for determining the eccentric "lead angle," which depends on "lap," "lead," and radius of the eccentric.

    I'm probably more confused about this than you are. Let's hope your plans are correct!

    Leave a comment:


  • aostling
    replied
    Originally posted by brian Rupnow View Post
    ... Now I have arrived at something totally new, the timing of the two cams at each side of the engine, in relationship to each other.
    I think those are more properly called eccentrics. This article refers to them as "eccentric sheaves," a term I have not heard of. https://en.wikipedia.org/wiki/Eccentric_(mechanism)

    I have my father's engineering textbook from the 1930s -- on reciprocating steam engines. Your splendid engine has inspired me to open its pages for the first time in ages.

    Leave a comment:


  • brian Rupnow
    replied
    Up until this point, I have been reasonably sure of what I was doing---as in "Okay, I've done all of this stuff before, so I'm not covering new ground here." Now I have arrived at something totally new, the timing of the two cams at each side of the engine, in relationship to each other. The solid model I have shows a separation of 120 degrees between the high point of the lobes on the two adjacent cams. The part which I have been referring to as the "reversing plate" has a total included angle of about 30 degrees. I have absolutely no idea as to whether this is correct or not. Whoever has created the 3D model I have worked from has done a sensational job, and I can proceed based on blind trust that he has modelled this relationship correctly, but I would really like to have a better understanding of how or why this works. If anyone out there can shed some light on this, I would really appreciate it.---Brian

    Leave a comment:


  • J Harp
    replied
    Nice work. That's going to be a good looking engine.

    Leave a comment:


  • brian Rupnow
    replied
    I'm very pleased with how the silver soldering went on my four eccentric strap sub assemblies. I got good flow all around the 1/8" rod at both ends, and good fusion between the steel rods and the brass ends. My "soldering fixture" worked like a charm. I have set one of the assemblies with an offset end up in the fixture for one shot, so you can see the spacer underneath the large end of the strap. I had no problem removing them from the fixture. A two hour soak in Citric acid and then some brisk scrubbing with my small brass bristled brush yields some very nice looking parts---and they are all exactly the same center to center distance.

    Leave a comment:

Working...
X