Chevy Van under hood vacuum chamber collapsed. Why?

1989 G-20 Chevy Van has this round vacuum chamber attached directly under the hood, it has one vacuum line attached to it. It used to be perfectly round but now it is football shaped, that is before I tried to use compressed air to put it back into shape. Now it's just toast. What is the purpose of this thing and why did it collapse? Too much vacuum? Too much engine compartment heat? Or something else? What is this thing called and if I plug the line can I drive without it and not damage anything else? Any help with this would be greatly appreciated.

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