Part 7 (1/2)
A. By increasing the lead.
Q. What is lead?
A. It is the amount of opening the port shows on steam end of cylinder when the engine is on dead center.
Q. Is there any rule for giving an engine the proper lead?
A. No.
Q. Why not?
A. Owing to their variation in construction, speed, etc.
Q. What would you consider the proper amount of lead, generally.
A. From I/32 to I/I6.
Q. What is ”lap?”
A. It is the distance the valve overlaps the steam ports when in mid position.
Q. What is lap for?
A. In order that the steam may be worked expansively.
Q. When does expansion occur in a cylinder?
A. During the time between which the port closes and the point at which the exhaust opens.
Q. What would be the effect on an engine if the exhaust opened too soon?
A. It would greatly lessen the power of the engine.
Q. What effect would too much lead have.
A. It would also weaken the engine, as the steam would enter before the piston had reached the end of the stroke, and would tend to prevent it pa.s.sing the center.
Q. What is the stroke of an engine?
A. It is the distance the piston travels in the cylinder.
Q. How do you find the speed of a piston per minute?
A. Double the stroke and multiply it by the number of revolutions a minuet. Thus an engine with a 12 inch stroke would travel 24 inches, or 2 feet, at a revolution. If it made 200 revolutions a minute, the travel of piston would be 400 feet a minute.
Q. What is considered a horse power as applied to an engine?
A. It is power sufficient to lift 33,000 pounds one foot high in one minute.
Q. What is the indicated horse power of an engine?
A. It is the actual work done by the steam in the cylinder as shown by an indicator.
Q. What is the actual horse power?
A. It is the power actually given off by the driving belt and pulley.
Q. How would you find the horse power of an engine?
A. Multiply the area of the piston by the average pressure, less 5; multiply this product by the number of feet the piston travels per minute; divide the product by 33,000; the result will be horse power of the engine.
Q. How will you find the area of piston?
A. Square the diameter of piston and multiply it by .7854.
Q. What do you mean by squaring the diameter?