[ Johan and Phil Dayson have been discussing flow measuring equipment.
 [ One somewhat confusing aspect is turbulent versus non-turbulent air
 [ flow through a constriction.  For example, air flow through a small
 [ bleed (as in a player piano valve) is turbulent, and so the plot of
 [ flow vs. pressure is non-linear.  But airflow through a large flat
 [ surface (such as pouch leather) is probably non-turbulent, and the
 [ plot is fairly linear.  See Phil's articles in the MMD Archives.
 [ -- Robbie

Phil Dayson wrote [in 990415 MMDigest]:

> I have always felt that the best way of reporting leakage measure-
> ments is as XX cubic inches per minute measured at XX inches of water
> column vacuum. ... This reporting method is, I feel, more intuitive
> than the resistance concept and thus may be better understood by many
> restorers.  ...  This is the method which I settled on in my leak
> test apparatus described in MMD  1997.02.05.08.

Thanks for making me aware of your earlier writing, only I could not
see how the apparatus was made.  I am eager to know how you measure the
flow over wide ranges.  I have tried with a slider plate with apertures
different sizes (range switch), and measured the differential pressure
with a U-tube manometer, and finally inferred the flow using the
Bernoulli law.  Is that the kind of thing Craig Smith is up to?

In the concrete situation when you have a device under your hands,
then you would want to know if it is good or not.  In this situation
your simple measure of flow rate is an ideal thing.

In your writing you give some examples that are really provocative to
the thought.  I believe figures like these are real gold to a restorer
in order to decide between failure and success.  It appears that some-
body who knows ought to write a table of typical or recommended airflow
rates at the various places in a reproducer piano for the MMD Archives.
Presumably this could list normal operating flows; I would imagine the
maximum permissible leakage to be to the order of 5 or 10 percent of
those.

Sorry I cannot contribute, lacking experience from that field.  My own
craze is to devise a band organ, and my interest in leaks came when my
'great inventions' did not work properly because of them.  I also saw
that Craig Brougher has told us you must test your materials.  When
doing that it is very nice if you can characterize a material as such
using a single number.

That is where my flow resistances come in, even if they admittedly
are more abstract.  There remains a chain of computation between such
a measure and a practical device where you have to account for specific
pressures and geometrical dimensions.

Presently I am measuring some bulk and sheet materials, and indeed
I am amazed at times at how different some of them behave from what
I expected.  But so far the resistance concept seems to hold.  At
these rather low rates the flow is normally laminar and proportional
to pressure differential.  Also I have not yet seen any effect of
increased leaking because of strain in leather, even if it is very
plausible.

I will be back later with a report; this needs double checking.
I will do what I can to adapt to a world of inches and no formulas.

Johan Liljencrants

 [ Nuts and bolts for autos from Japan and Europe are metric sizes,
 [ and so most of now have some metric tools in the toolbox.  But the
 [ archaic English system of inches and feet is still used when des-
 [ cribing organ pipes and blower "windage" requirements.  In the
 [ modern scientific laboratory the U-tube manometer reads centimeters,
 [ but player piano and organ techs around the world still measure
 [ inches of pressure or vacuum with a water gage.  Welcome, Johan,
 [ to the bygone era of wood and leather !  :-)   -- Robbie