H. W. Stephenson Monograph
By Phil Dayson
I hope the subscribers can tolerate yet another question/thread on the subject of valve travel.
My question is concerned with a monograph of some 300 pages published in 1993 by H. W. Stephenson, Isle of Man, UK. The title of the monograph is "In Search of Hofman -- An inquiry into the technology of the pneumatic reproducing piano".
This is a virtual PhD thesis that must have taken years of work. It contains a huge amount of information never before seen. For example, there are a number of graphs which show pouch suction, valve lift, hammer rise, tracker bar inlet area, all plotted against time in milliseconds
In this monograph Mr. Stephenson also shows a plot of hammer velocity vs. chest vacuum for a number of different valve gaps between 0.020" and 0.075". The graphs indicate little variation in hammer velocity and thus in loudness for the different gaps.
Mr. Stephenson says "variation of valve lift anywhere between 0.020" and 0.075" has no significant effect, so that it would not appear to be worth while to lavish time and care on determining what clearance to use, or even on effecting uniformity. ... Anywhere between 0.035" and 0.050" would be likely to be satisfactory."
This statement is absolutely _contrary_ to the opinion of most restorers. Why the difference?? I have no reason to doubt the accuracy of Mr. Stephenson's work. Is there a factor other than hammer velocity at work? Any comments?
Philip Dayson
[ Lets hear your views, everyone. Please say if you are talking about
[ Mr. Stephenson's experimental technique, the data gathered, or his
[ conclusions. This is a fine topic; thanks for your letter, Philip.
[ Can someone tell us how to get a copy of the monograph?
[ -- Robbie
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(Message sent Mon 24 Feb 1997, 02:17:37 GMT, from time zone GMT-0800.) |
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