32.  Q. What is a direct motion valve gear?  What is an indirect motion valve gear?

A. A direct motion valve gear is one in which the valve moves in the same direction as the eccentric rod, that is doing the work, in many cases no rocker arm is used.  In case a rocker arm is used, both arms point in the same direction like the letter U. An indirect motion valve gear is one in which the valve moves in an opposite direction to the eccentric rod doing the work.  A rocker is used in which the arms point in opposite directions from the shaft connecting them.  Owing to the design and construction of the Walschaert valve gear, it is a direct motion gear when the engine is running in one direction with the link block in the bottom of the link, an indirect motion when the engine is running in an opposite direction with the link block in the top of the link; usually direct motion when running forward.

33.  Q. How can you detect the difference between a blow in valve or piston packing?

A. A blow from the valve is more constant and has a somewhat different sound, while a blow from cylinder or piston packing will blow stronger at the beginning of the stroke and gradually decrease as the stroke is completed.

34.  Q. How would you place engine to locate broken admission steam ring in piston valve?

A. Would place engine on quarter, reverse lever in center so as to cover ports, then open throttle; and the steam will blow out of cylinder cock at the end of cylinder where broken valve ring is located.

35.  Q. How would you locate broken exhaust ring in piston valve?

A. Watch the cross-head when engine is working steam.  As there will be three normal and one light exhausts, you can determine on which side of the engine the light exhaust takes place.

36.  Q. What is meant by lead?  What by line and line?

A. Lead is the amount of port opening for live steam to cylinder ahead or back of piston when the piston is on the dead center.  If the steam edge of the valve is in line with the edge of the steam port when the piston is on the center, it is said to be line and line.

37.  Q. What is meant by steam lap?

A. The distance that the valve overlaps the live steam edges of the steam ports when it is in the center of its travel over the seat.  This distance is measured at one end only, although the valve laps equally at both ends.

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.

39.  Q. What is meant by release?  What by compression?