Rough and Tumble Engineering - novelonlinefull.com
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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?
A. Multiplying it by itself. If a cylinder is 6 inches in diameter, 36 multiplied by .7854, gives the area in square inches.
Q. What do you mean by average pressure?
A. If the pressure on boiler is 60 pounds, and the engine is cutting off at 1/2 stroke, the pressure for the full stroke would be 50 pounds.
Q. Why do you say less 5 pounds?
A. To allow for friction and condensation.
Q. What is the power of a 7 x 10 engine, running 200 revolutions, cutting off at 1/2 stroke with 60 pounds steam?
A. 7 x 7 = 49 x .7854 = 38.4846. The average pressure of 60 pounds would be 50 pounds less 5 = 45 pounds; 38-4846 x 45 = 1731.8070 x .333 1/3, (the number of feet the piston travels per minute) 577,269.0000 by 33,000=17 1/2 horse power.
Q. What is a high pressure engine?
A. It is an engine using steam at a high pressure and exhausting into the open air.
Q. What is a low pressure engine?
A. It is one using steam at a low pressure and exhausting into a condenser, producing a vacuum, the piston being under steam pressure on one side and vacuum on the other.
Q. What cla.s.s of engines are farm engines?
A. They are high pressure.
Q. Why?
A. They are less complicated and less expensive.
Q. What is the most economical pressure to carry on high pressure engine?
A. From 90 to 110 pounds.
Q. Why is high pressure more economical than low pressure?
A. Because the loss is greater in low pressure owing to the atmospheric pressure. With 45 pounds steam the pressure from the atmosphere is 15 pounds, or 1/3, leaving only 30 pounds of effective power; while with 90 pounds the atmospheric pressure is only 1-6 of the boiler pressure.
Q. Does it require any more fuel to carry I00 pounds than it does to carry 60 pounds?
A. It don't require quite as much.
Q. If that is the case why not increase the pressure beyond this and save more fuel?
A. Because we would soon pa.s.s the point of safety in a boiler, and the result would be the loss of life and property.
Q. What do you consider a safe working pressure on a boiler?
A. That depends entirely on its diameter. While a boiler of 30 inches in diameter 3/8 inch iron would carry I40 pounds, a boiler of the same thickness 80 inches in diameter would have a safe working pressure of only 50 pounds, which shows that the safe working pressure decreases very rapidly as we increase the diameter of boiler. This is the safe working pressure for single riveted boilers of this diameter. To find the safe working pressure of a double riveted boiler of same diameter multiply the safe pressure of the single riveted by 70, and divide by 56, will give a safe pressure of a double riveted boiler.
Q. Why is a steel boiler superior to an iron boiler?
A. Because it is much lighter and stronger.
Q. Does boiler plate become stronger or weaker as it becomes heated?
A. It becomes tougher or stronger as it is heated, till it reaches a temperature Of 550 degrees when it rapidly decreases its power of resistance as it is heated beyond this temperature.
Q. How do you account for this?
A. Because after you pa.s.s the maximum temperature of 550 degrees, the more you raise the temperature the nearer you approach its fusing point when its tenacity or resisting power is nothing.
Q. What is the degree of heat necessary to fuse iron?
A. 2912 degrees.
