The reservoir holds reserve vac to operate the headlights AND the HVAC components when you get heavy on the throttle. Without the reserve tank, the vac operated components would return to their "rest" positions every time you mashed the go pedal very hard. If you've ever driven an older(and some newer) Ford with A/C you know what I mean....you get on the throttle a little, and the A/C starts blowin out the defrost vent....aggravating as heck.
There's no real reason for the can to deform like that with "normal" vacuum unless the can is bad in some way. Perhaps it was just too thin....just because it's new don't mean it's good. A gas engine will only produce so much vacuum...23-23 inches on decell would be considered normal for a good running engine with no leaks.....not enough to suck the reservoir inside out like that.
You can certainly connect the relays to straight vacuum without the reservoir with no ill effects other than the previously mentioned issues with stuff moving during heavy throttle....headlights have been known to flop open/shut while driving. I'd sure be suspicious of a new reservoir that failed that quickly.......
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Joel Adams
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