paraphrasing:

The vacume valve can be one of two types
  one without spring: waits until engine is hot to build pressure
Does this depend on the rate of expansion?


Some of the other things I have learned from our discussion that are
not in this text:

We want air trapped in the system to provide a cushion.
Air/Liquid separator valves are not used. i.e. float valve.
The A-can is our air/liquid separator.

With a reasonably designed A-can negative Gs can be had for short
periods. i.e. keep it from spilling.

Blake Lewis

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Yes the text does not discuss the latest design that does away
with the coolant recovery tank. Hopefully the trapped air is
above the coolant and not embedded within it in the latest systems.

With careful placement of vent lines most temporary negative G's
situations will not result in a loss of coolant from the coolant recovery tank.