Dear readers,  It has been known that the larger pipe-organs started
to play well only from the moment blowers came into play.  If you look
at book-music cut for big organs before the blower era, you see one
note in the melody and one note in the counter-melody, all the while
going easy on the registration.  After the blower was installed,
arrangers used four notes in the melody and big registration clusters
in the forte parts, which made a big difference.

The bellows are just too small to do the job in bigger organs.
Increasing the size would be very impractical ('twould be larger than
the organ case!) and impossible to turn by hand.

With certain types of weather, when the working of the wooden chests
starts to press against valves opening them ever so slightly (which
creates little leaks all over), the problem can be more noticeable.

About a big mistake some people make -- the reservoir should actually
be called a regulator, and not be considered as a "container that
holds a big stash of air for such a time when we hit a crisis!"  ;-)
Actually, the amount of air inside the reservoir amounts to very
little, just enough to overcome the heavy, but short, hits.

No, in reality, the reservoir is a regulator.  In the case of an organ
with pumps, the regulating is done with a release valve on top of the
so-called reservoir.  More or less pressure opens the valve more or less
according to the springs pushing down on top of the regulator.  This
process makes sure that the pressure inside the regulator is according
the spring-pressure on the outside.  It works well, and measurements
show that the pressure is mostly within 5% of the target.

There should always be air coming out of the release valve.  From the
moment the release valve closes completely, running out of air is just
around the corner.

If you choose a blower, you must select one with enough pressure as well
as enough flow.  I read in the MMD the suggestion of using a blower of
the type used on inflatable toys (castle, water slide).  These blowers
produce plenty of flow but not enough pressure for most, if not all,
organs.  This is also the reason why they are fairly quiet.  I'm not
sure as I do not know these blowers very well, but they run probably
at about 1200 rpm with a small diameter (little pressure) but wide (for
big flow) single blade.

Organ blowers need to increase pressure.  This can be done by :

 - increasing the shaft RPM (making the blower a lot more noisy);

 - increasing the blade diameter (making the blower a lot bigger);

 - increasing the number of blades, where the first blade blows upon
   the next and so on.  This seems the better solution if you want to
   keep size and noise within acceptable limits;

 - a combination of the above.

An organ needs a blower which should rate about 1/3 higher pressure
than what the organ pipes are voiced to.  For an organ which is loud,
the pipes are voiced around 9 inches (230 mm) water gage pressure.
For such an organ you need a blower which can produce about 13.5 inches
(350 mm).  You need this extra 1/3 of pressure because the blowers
pressure will drop a fair amount during playing, according the amount
of air used.

Then the next choice you have to make is budget against noise.  The
more money you spend (up to 4000 US dollars), the more silent the
blower will be.  For our organs we choose between three blowers :

 - one we build ourselves, but the pressure is at about 10 inches,
   (254 mm), not that high.

 - an English multi-blade blower which gives 13.5 inches (350 mm)
   which is fairly quiet.

 - a German multi-blade blower which gives 13.5 inches (350 mm)
   and which is very quiet.

You can (re)use an existing bellows system by cutting a hole in the box
under the regulator (reservoir) and blow the air of the blower straight
into it.  It is not the very best solution, but it works satisfactory,
it is little work, and removing the blower at a later time is easy.
You only have to close the hole that you cut before.

Best regards,

Tony Decap BVBA - Orgelfabriek DECAP
2200 Herentals, Belgium
http://www.decap-herentals.be/ 

 [ "BVBA" means "Private Company with Limited Liability".  Tony writes:
 [
 [ "Tony Decap BVBA is just an in-between company.  Now we are working
 [ to create a new type of structure which will simplify things.
 [ Soon our company "Decap-Herentals" will celebrate its 75 year
 [ anniversary, so there is a party in the making!  75 years ago my
 [ grandfather decided to leave his brothers in Antwerp and start his
 [ own company in Herentals.  We wonder if this was a smart move, but
 [ who can tell now...
 [
 [ "Our business is doing well.  Work has been flowing in steadily,
 [ we have delivered over 100 master-accordions, and the new 121-key
 [ organ is nearing completion.  Our quality has been high and customers
 [ are very pleased with the work, also over longer periods of time.
 [ We hope, like all of us, that the economic crisis will not bring our
 [ good fortune to a standstill.  But we are fairly confident.  If you
 [ are in the neighborhood please drop in!"
 [
 [ -- Robbie