508
THE NEW ZEALAND GAZETTE.
[No. 16

adjacent crank. (NOTE.—The horizontal distance between the centre of gravity of each balance-weight and the centre-line of the adjacent cylinder is 15 in.)
(50 marks.)

7. A solid sphere of steel 3 ft. diameter is mounted in bearings and rotated about an axis through its centre by means of a belt and pulley. The journals are 4 in. diameter, and the coefficient of friction at the bearings is 0·05. When the sphere is revolving at 200 revolutions per minute the driving-belt breaks, and its motion is thereafter affected by friction at the bearings only. Find, neglecting the weight of the driving-pulley and journals, how many minutes elapse from the time when the belt breaks till the sphere comes to rest. (NOTE.—The specific gravity of the material is 8. Formulae used in solving this problem should be proved.)
   (45 marks.)

8. Explain the principles involved in the action of steam-turbines of the impulse and reaction types, and enumerate the factors upon which the efficiency of each of these types of turbine depends. State the meaning of the terms “pressure compounding” and “velocity compounding” as applied to turbines, and describe the methods of pressure compounding and velocity compounding usually adopted.
   (45 marks.)

Second Day: 9.30 a.m. to 12.15 p.m.

NOTE.—Candidates are not permitted to attempt more than three questions in this paper.

9. A Diesel engine cylinder is 30 in. diameter and the length of the stroke 5 ft. The crown of the piston is dished to a depth of 4 in., the radius of curvature of the concave surface being 20 in. If the ratio of compression is 13, what is the piston clearance when the crank is on the top dead point? (NOTE.—The clearance required is the distance between the top of the piston at its periphery and the under surface of the cylinder-head, which is assumed to be flat. Formulae used in solving this problem should be proved.)
   (45 marks.)

10. A six-cylinder four-stroke cycle single-acting heavy oil-engine develops 1,650 indicated horse-power at 120 revolutions per minute. The fuel consumption is 5¼ tons per day of 24 hours, and the calorific value of the fuel 19,000 British thermal units per pound. The cylinder diameter is 24 in., the length of the stroke 42 in., and the compression ratio 9. The engine is of the airless-injection type, and it is assumed that the fuel is admitted and completely burned when the piston is at the in-centre; and also that 20 per cent. of the total heat of the fuel is given up to the cooling-water while the piston is in this position. The specific heat of the gas is 0·17. If the temperature of the air entering the cylinders is 80 degrees F., find—(a) the temperature and pressure at the end of the compression stroke, the index to the compression curve being 1·4; and (b) the maximum pressure and temperature when ignition takes place. (NOTE.—One pound of air at atmospheric pressure and 32 degrees F. occupies 12·4 cubic feet.)
    (50 marks.)

11. In a De Laval turbine steam leaves the nozzles, which are inclined at an angle of 20 degrees to the plane of the wheel, at a velocity of 3,000 ft. per second. The total steam consumption is 5,000 lb. per hour, the speed of the wheel 9,545 revolutions per minute, and the mean diameter of the blade circle 2 ft. Assuming that the blade angles of entry and exit are equal and neglecting all losses, find the horse-power of the turbine.
    (55 marks.)

12. Describe a system of pulverized coal firing as applied to marine boilers. Discuss the relative merits of pulverized fuel-firing and hand-firing methods with special reference to reliability, maintenance, and economy.
    (40 marks.)

Second Day: 1.30 to 4 p.m.

NOTE.—Candidates are not permitted to attempt more than three questions in this paper.

13. A vessel of 5,000 tons displacement heels 6 degrees when a weight of 8 tons is moved transversely across the deck a distance of 25 ft. A double-bottom fuel tank of uniform width 20 ft. long and 40 ft. wide is partly filled with oil at the time when the