Such as the intake stroke bringing air in. Air pressure is the correct
answer but 'suction' should also be correct, by definition.

Someone said that suction can't exist without air in the first place.

Fun little time waster though, eh?

Regards,
Joe Agro, Jr.
(800) 871-5022
01.908.542.0244
Automatic / Pneumatic Drills: http://www.AutoDrill.com
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V8013-R