Q. What is the horse-power developed by an engine, say 12 × 24 inch, running 125 revolutions per minute, with 40 pounds mean effective pressure?
A. Area = 12 × 12 × .7854 = 113.0976 sq. ins.
Piston speed = 24 × 2 × 125 ÷ 12 = 500 feet per minute.
Then (113.0976 × 500 × 40) ————————————————————— = 68.544 H. P. 33000
A. It is an engine in which a single valve controls the admission and distribution of steam to both ends of the cylinder, or a common slide valve engine.
A. An engine which has separate steam and exhaust valves for each end both top and bottom of cylinder, such as a Corliss engine.
Q. Into what three classes are engines divided with reference to the manner in which they are governed?
A. Throttling engines, Automatic cut-off and Governor engines.
A. An engine in which the amount of steam supplied is automatically cut off at various points in the stroke, in accordance with the load and pressure. In Throttling engines the volume admitted is constant and the pressure varied. In Automatic cut-off engines, steam is admitted at the highest available pressure, and the volume is varied to meet the requirements of the load. In Governor engines, the steam is admitted and cut off by the governor.
A. An engine in which the amount of steam supplied is regulated by changing the pressure at which it enters the cylinder in accordance with the variation of the load.
A. An engine in which the supply of steam is regulated by the governor.
Q. Into what classes may the Automatic cut-off engine be divided?
A. Into two classes: The four valve engine, in which the cut-off is usually effected by a detaching mechanism or trip under the control of the governor; the single valve engine, in which the point of cut-off is varied by changing the amount of travel of the valve.
Q. Give examples of the single valve type.
A. High speed, self-contained engines which have shaft governors.
A. High rotative speed, compactness, portability, light weight and simplicity.
Q. Are they more economical than the four valve engine?
A. No; the four valve engines are the more economical.
Q. Give a prominent example of the four valve engine.
Q. What is meant by an engine running “over”?
A. The top of the drive wheel running away from the cylinder.