MECHANICAL ENGINEERING VII.

1. (a) Calculate and sketch a train of gears for a velocityratio of 27: 490, no gear to have more than 120 teeth or less than 12, and using the least number of wheels.

(b) The table of a planer is moved back and forth by a rack underneath it which gears with a pinion of 12 teeth. On the pinion shaft is a gear wheel having 45 teeth; gearing with this is a pinion having 15 teeth; on the same axis as this last pinion is a wheel of 30 teeth, and gearing with this is a pinion having 12 teeth; upon this pinion the pulley is placed. If the table is to move at the rate of 20 feet per minute, find the number of revolutions per minute of the pulley.

Diametral pitch, 2.

2. Give an example of epicyclic gearing, and, assuming numerical values, show how to find the velocity ratio of such a train.

3. The distance between the centres of two parallel shafts is 5'-3". They are to be connected by a pair of spur gears so that the angular velocity ratio will be 4:5..

Calculate pitch diameters, numbers of teeth for diametral pitch No. 2, and circular pitch.

Describe in detail the construction of involute teeth for these gears, and explain why gear wheels with involute teeth may be substituted for rolling pitch surfaces.

4. Deduce, by the instantaneous centre method, the general expression for the angular velocity-ratio in transmission of motion from one centre to another by linkwork.

5. Explain the use of the Zeuner valve diagram in connection with plain slide valve engines, and show how to find the points of admission, cut-off, release and compression, and the lead by means of the diagram. Prove the correctness of this method.

POWER PLANT ECONOMICS.

1. How would you determne the relative commercial value of two fuels ?

2. Enumerate the various losses of energy between the coal pile and the switchboard, giving approximate percentages, based on initial energy.

3. Give a list of the various items which must be considered in estimating the cost of power.

66

4. Define the terms: "depreciation," "sinking fund," amortization," "obsolescence," "fixed charges," and "capital account."

5. State the general conditions which are favorable to the following types of plants: (a) Reciprocating engine, (b) gas engine, with or without producer, (c) high pressure steam turbine, and (d) low pressure steam turbine.

6. Give reasons for the difference in performance of the low pressure steam turbine and a reciprocating engine, working under the same conditions.

7. The capacity of a certain plant, composed of two 1000 H.P. and one 500 H.P. reciprocating engines, is to be increased by replacing the 500 H.P. unit with either a 1500 H.P. low pressure turbine or a 1200 H.P. high pressure turbine. The cost of the turbines, including generators, is $40 per H.P., and the cost of coal is $3.00 per ton. The second proposal will require 250 H.P. of boiler capacity more than the first, at a cost of $25 per H.P.

Assuming the annual output to be 4X106 H.P.-hours, fuel consumption for the combination of reciprocating engine and low pressure turbine to be 2.5 lbs. per H.P.-hour, and of the alternative combination 2.8 lbs., which scheme would be the more economical? Assume appropriate values for fixed. charges.

8. The fuel consumption in a certain plant increases 20% when the engines are operated non-condensing. If operated in this way, the owner can, by expending $20,000, sell 50% of the exhaust steam for a period of six months at 40 cents per 1000 lbs. If the normal fuel consumption during this six months is 1500 tons of coal, costing $3.00 per ton, will

Allow

it be profitable for the owner to make the investment of $20,000, and if so, what will the annual profit be? 14% for fixed charges.

DESCRIPTIVE GEOMETRY.

1. A cube, (2) inches, is located in the first quadrant, one edge ab coinciding with the ground line. Thus the face abcd is contained in the vertical plane of projection and the face abfe in the horizontal, abde forming a solid angle.

A diagonal is drawn from d to f. Determine the distance from the diagonal to the edge which is parallel to and in the same vertical plane as bf.

2. Determine the shadow of a cube, 23 inches, placed so that one of the diagonals is perpendicular to the horizontal plane of projection, and one edge contained in the vertical plane.

3. The distance between the traces of a line in the first quadrant is 4 inches, the traces being equidistant from the ground line and the vertical projection of the line inclined 30° to the ground line. Determine the angle which the plane of the shadow makes with the horizontal plane of projection.

4. The projections of a diagonal of a cube, (2) inches, resting on the horizontal plane of projection, and having one surface parallel to the vertical plane of projection, are given. Required to draw the projections of a line contained in the horizontal plane of projection, and making an angle of 120° with the given diagonal.