The newer versions (still ancient - 470A's) have a ballast vacuum
assist system that takes care of this requirement. Upgrading to the
vacuum assist was never an option from ABI. The vacuum assist system
operates in the range of 13 - 21 inches of mercury. Not a great vacuum
but sufficient to assist in the opening and closing of the valves.
My question is: What is the maximum vacuum that the valves and membranes
will tolerate?
Thanks in advance,
alex
Alexander W. Bell
Dept. Anat. & Cell Biol.
McGill University
Montreal PQ
H3A 2B2 CANADA
phone (514)398-1393
fax (514)398-5047
email ehjb@musica.mcgill.ca