During an upstroke this closes, and the other opens; the reverse happening during a downstroke.
Her axe shone, on the upstroke, on the downstroke, as she hacked at his hand.
During the upstroke the cup collapses inwards and allows air to pass by it.
After the downstroke is completed, the teeth A will cut on the upstroke, the teeth B cutting on the downstroke, etc.
The stroke on the left side of that capital is first a down stroke, which is almost exactly retracted by an upstroke.
The parts are in correct mechanical balance because two pistons are on the upstroke while the other two are descending.
We have a downstroke on the left side of the letter which is almost exactly retracted by the upstroke.