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"The relative positions of crank, eccentric and valve when the exhaust closes on the crank end and compression begins. Between these two positions the steam is expanding in the head end and exhausting from the crank end." —Derr, 1911

Steam Engine Valve with Lap Steam Where Slide Valve is Closed

"The relative positions of crank, eccentric and valve when the exhaust closes on the crank end and compression…