Hi,  This is a response to John McClure's letter.

I would be extremely careful trying to move the pressure/vacuum source
away from the unit.  The hose must be airtight without any question,
but this is the least of the problem.  The main problem is the loss of
air pressure and debied [air flow] due to the resistance of the hose.

We have experienced and measured pressure and flow loss any time we
moved away from the source, no matter what you do to try to prevent
this.  Pressure loss comes from friction of the air molecules against
the side of the hose, turbulence of all kind that is created when air
molecules collide with some obstacle (like a ripple in the hose) or
each other, etc.

So John, extreme care should be taken in this matter.  I can not say
that it would not work in your case, but I can tell you for sure that
it will _not_ be an improvement.

As we have to deal with this problem also, you may read on about some
solutions we came up with.

Some rules of thumb:

- Mount the blower as close to the unit as you can.
- Always go from big to smaller tubes, thus avoiding a bottleneck.
- Never chain chests together going through all kinds of air traps,
   but feed them individually
- Keep tubes as short as possible.

- Try to minimize the amount of elbows;
- If you have to use them, never make a 90-degree bend,  but try to
   make the curves smooth and gradual, so that the air does not hit a
   brick wall going 50 miles an hour, with all turbulence and resistance
   that comes with it.

- Try to make the diameter of the tubes a little bigger than you need,
   but within reason.  This will lessen the resistance.
- Use tube that does not change shape with pressure.
- Avoid using flexible tube.  These usually are not 100% smooth on the
   inside, and they behave a little like a balloon, expanding with
   pressure.

- Be aware: two tubes with a diameter of 50 mm is not equal to one tube
   with a diameter of 100 mm.  Some people may think this is funny,
   but I have seen this done more than once.

All this rules taken individually may not seem important, but together
they may make the difference you need.

Problems like the ones described above is one of the reasons that we
invented the computer controlled servo-regulator that can be installed
in each separate wind chest.  This gives you the advantage that you can
transport the air straight from the blower up to the chest.  There will
be some pressure lost, but in this case it does not matter, as the
pressure and flow from the blower is higher than the one you need (or
should be).  The desired pressure is then created at the location it is
needed.

Some extra advantages of this system are that

- you can build an organ that incorporates multiple pressures.
   We've experienced that different registers sound better at different
   pressures.

- you can add any pressure curve from the computer to the pipes.
   This can be any kind of vibrato, with free to chose depth and/or
   speed, even variable over time.  Or this could be de-tuning until
   some degree, or over-blowing attacks on the flute, etc.

We are building a complete system like this for an organ currently
built by Mr. Pluer from Holland.  This organ includes about 13 MIDI
systems so that each pipe can be addressed individually, and all
registers are in separate volume chests that can be individually
controlled from the computer.  Each chest has his individual computer
controlled pressure regulator.  This organ will be ready by the end of
this year, and we are really very anxious to try out the possibilities
of this new system.

Brothers Tony & Frank Decap
Gebroeders Decap Herentals
Belgium
http://www.decap.be/

 [ Thanks for the nice article, Tony.  I think I correctly translated
 [ the Dutch/Flemish word "debied" as "flow", but now I'm curious:
 [ what are the names and units, in the organ trade, for air pressure
 [ and air flow, in Dutch and German and French and English?
 [
 [ Pressure:
 [   (E)  pressure - pounds per square inch, or inches water column
 [
 [ Flow:
 [   (E)  flow - cubic feet per minute?
 [   (NL) debied -
 [   (D)  die Stroemung? - cubic metres per minute?
 [   (F)  la circulation? -
 [
 [ -- Robbie