In a recent posting [240712 MMDigest], David Krall asks about
a Recordo pump and which Recordo system it used. The pictures show
that the vacuum regulator is of the 'Choker type' as defined by
Bob Billings in his article, "Recordo Banner Flies Again", in the
AMICA Bulletin. This type uses the 4 ports to give a 10-level system.
Bob calls this the Recordo 'B' sysytem.

[ https://stacks.stanford.edu/file/druid:tj495jx9542/08-01.pdf 

In the MMD Archives is a paper that I had prepared which discusses the
vacuum level values for each of the three Recordo systems. The paper
can be a bit difficult to find, but persist with looking for it under
my name, Paul Rumpf.

[ https://www.mmdigest.com/Attachments/21/08/10/210810_205231_RecordoA-decibels.doc 

Also in the Archives is an Excel presentation which gives the vacuum
levels for each port setting. The results are plotted as a graph as
well.

[ https://www.mmdigest.com/Attachments/21/08/10/210810_205231_RecordoA-design.xls 

The vacuum level in the choker pneumatic is the same as in the
individual port pneumatics when selected. Effectively, the force
developed in the choker pneumatic is offset by the force developed
in the port pneumatics.

The Excel sheet shows the area of the choker pneumatic board is
4 square inch, and the port pneumatics have smaller areas. The size
of the pneumatics is given in the Excel sheet 1. These sizes were
'guessed' from pictures of a vacuum control box, and then assumed
that the area of each pneumatic board was a multiple of 1/16 inch.

More information on Recordo and the design of the 'Leaker type'
Recordo regulators is in the book, "Player Piano: Servicing and
Rebuilding", by Art Reblitz.

I turned 82 in May, so I got to get all the stuff in my head into
the Archives!

Hope this helps,

Paul Rumpf
in Melbourne, Australia