38. Q. What is meant by exhaust lap? What by exhaust clearance?

A. Exhaust lap is the distance that the exhaust edge of the valve

overlaps the exhaust edge of the steam port when the valve is in

central position. Exhaust clearance is the opening between the exhaust

edge of the valve and the exhaust edge of the steam port with valve in

central position. If the valve has neither exhaust lap or clearance it

is said to be line and line.