Don Barton's observation [130612 MMDigest] sounds wrong.  Normally,
on a double valve system, the primary valve provides the 'bleed' for
the secondary valve -- i.e., open to atmosphere -- so no bleed is
required for the secondary pouch.

With assumptions (and specifications) about porosity of pouch
material, a bleed may be omitted in the manufacturing process for
primary valve pouches, _but_ the responsiveness of the primary valve
has to be a consideration.  I'd be interested in other readers'
experience.

Paul Rumpf
Melbourne, Australia