I have posted on this topic before, not as an expert but only relating
personal experience.

This all started with a question on the supply to a Reproduco Organ.
I am sure all the engineering opinions are correct as to drawbacks with
long supply runs.

The fact remains that there are many organs, large and small, with long
supply runs, even though the idea is said to be "keep it close."  One
must assume on these original installations, all the distance factors
were taken into consideration and compensated for in some way, because
they all worked!

Getting back to the Reproduco unit.  I suspect that very few of these
instruments were exactly the same.  I personally have yet to see two
that were alike.  Just some of the variables are: coin operation, foot
pedals, mandolin rail, large roll, small roll, air motor roll drive,
electric motor roll drive, single roll frame, double roll frame, chimes
-- and the list goes on.

Some Reproduco units have a combination suction and pressure pump.
Some have a blower located remote, and a box pump in the top of the
instrument for the suction.

The copy of the original literature that I have to refer to shows the
pressure regulator and reservoir mounted on the back of the piano.

My Reproduco has the identical blower as pictured on the original
instruction sheet, however, the regulator and reservoir are mounted
on top of the blower unit, which is remote.

The regulator is nothing more than a huge slab of pig iron that can
be moved closer to or away from the open end of the reservoir, and this
does change the pressure delivered at the organ.  The weight of this
pig iron on the reservoir, does the same work as outward pressure
springs that would be mounted externally.

There is a spill valve inside the reservoir that is just a knife valve
and this is connected to the movable board of the bellows (reservoir)
with a strong cord, also adjustable by the length of the cord.  Should
the reservoir fill and open too far, it pulls on the cord and excess
pressure spills off.

My expert pipe organ man, Mel Wilitz, made several trips to the
basement to shift the weight on the blower unit, until he achieved the
pressure and flow volume he required to tune and voice the pipes.  He
said the arrangement and location was awkward, but not unusual compared
to all he had encountered during his life time of experience.

Bottom line: it's just a matter of what works. The people installing
and servicing these instruments in yesteryear were very resourceful and
just did what needed doing.  End result: They worked, they worked well,
they worked for a very long time, and now, because of devoted
collectors, these wondrous instruments are playing again!

In Music - Ken Vinen, Stratford, Ontario, Canada
(www.woodsvilla.orc.ca)