Dear Geoff,
Sorry for the delay in answering.
> To correct myself on the A3, there wasn't much play in the valve gear,
> it was in the reverser and the linkage to the valve gear, more for my
> satisfaction than the expectation of better running, as it runs very
> well now.
It is the same set of components that we are talking about - the
reverser and all the links between the valve and the reverser.
As I indicated in my original email about this problem, the running
qualities amazingly are not that much affected by the asymmetry in
the actual openings of the steam inlets.
(This asymmetry is due to the wrong valve setting, due to the play
in the above components which results in a `lag' or `hysteresis'.)
But the actuall pulling power may be affected. I have only `tested
by eye' on a very primitive bicycle air pomp. Probably proper testing
on constant pressure of air or steam with load on wheels would provide the
answer to the possible power loss and irregularity of running which
this discussed asymmetry may cause.
>
> I did assemble a C&S Mogul--the play in all parts of the valve gear was
> "overplayed".--It was sloppy! There was one fellow, whose name I can't
> recall, who solved the problem by manufacturing all new valve gear!
> Probably the only way to sure success! I appreciate your input and
> experience on assembly and testing.
Let's put it like this: it is indeed somewhat looser than I would
have expected it to be. I found that the major contribution to this
play in the C&S Mogul comes from the small `die block' in the
expansion link which is probably about 0.2-0.3mm too small. I
actually asked the amazingly quick and helpful Aster Service to send
me the replacement blocks, but they were identical in size (surprise,
surprise... ) Of course fabricating new blocks would take maybe 5
minutes for someone with the proper tools and machining experience but I
have got neither, so I will at some stage perhaps look for someone to
do this for me. An additional offender is the centre bushing in the
supports/mountings of both the expansion links. The play there is as
much as 0.2mm and again the replacement story repeats itself...
Altogether there are not that many other links and I find
that if this 0.5mm play would be reduced or eliminated, there would
perhaps be 0.1-0.2 at most left altogether.
But, in agreement with your findings and opinion, this may be perhaps
cosmetic. What is however most alarming for me (as I have absolutely
no experience with Stephenson valve gear and reversers) it seems
that the running on very, very small opening of the valve gear with
reverser just off the centre position, while it indeed slows the
running speed significantly, also induces a rather violent and
irregular running characteristic. I wonder whether this is also
the case in real life, full size engines? If not, can this be helped
in a simplified small-scale engine? Is this a matter of timing which
can be changed or does the valve gear need to be altered in order
to provide different timing characteristics?
Thank you for all the help and happy steaming!
Zbigniew
>
> Steam on,
>
> Geoff.
>
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> Dear Geoff,
> >Thank you for your kind words. As I elaborated on in another email
> >just sent, I am still hesitant about the gap. Measurements convince
> >me, although the extra amount of work and the need to shop for the
> >components may be a strong counter-argument. I haven't decided yet.
> >I have to remark that my efforts to keep every Joule of energy in
> >place should make me a perfect Dutchman;^)! But as to my origins,
> >they are more steam-and-narrow-gauge-land than under-water-land!
> >I am most intrigued by your work on removing the play in the valve
> >gear. I believe this is a long researched phenomenon in the C&S Mogul,
> >but I have recently been playing around with the valve gear wondering
> >if the play of about 1 mm should not be reduced... (the steam inlets
> >in the cylinders are about 1.5 mm!!) In effect symmetrical steam
> >transfer is only possible in one direction (say forward) while
> >the other direction will be strongly asymmetrical (only one side of the
> >cylinder will receive steam). Surprisingly, air test only shows
> >later activation of the movement in the asymmetrical direction, not
> >a much more violent and irregular (un-smooth) running. In fact, for
> >small openings of the reverser the running is very nervous and violent
> >in both directions (symmetrical and asymmetrical steam inlet opening)
> >to the same degree. This would mean that there is little practical
> >need for removing the play, it would only shorten the dead region
> >in the reverser range but not improve the running for small opening.
> >Happy steaming!
> >Zbigniew
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