7. A safety-valve, 6 inches diameter, has a spiral spring 5 inches in diameter outside, and inch thickness of steel: what is the pressure per square inch?

; where s is the thickness of steel, and d= diameter of spring from centre

of steel to centre of steel.

8. What is the atmospheric pressure in lbs. per square inch in the following diagram, (the weather barometer showing 29 inches), if 2.04 inches of mercury were equal to 1 lb. per

square inch?

Top of cylinder.

Steam side.

Fig. 137.

Scale of 16ths
to an inch.

Bottom of cylinder.
Steam side.

NOTE.-According to the density of steam at 18 lbs. gross pressure, that is, about 3 lbs. above the atmosphere by the steam gauge, it would take just 35 lbs. weight of steam per hour to produce one I.H.P., if worked without expansion, and also without back pressure or other loss. At higher pressures (less than 35 lbs.) steam would produce the same result; but there are several considerations which lead to the adoption of 35 lbs. as a convenient standard in estimating approximately the cost of evaporation and of H.P. from indicator diagrams,

P.2. 9.9

Line of perfect vacuum.

P.J. 11.5

9. Draw the line of perfect vacuum on the diagram, and measure off the pressure denoted by P1 and P2, viz., the gross pressure at of the stroke from the beginning for both strokes, P, being the down, and P, the up stroke, and determine the tons of steam for 24 hours as given by the card.

Rule.

IO.

(P1 P2) del r
149000

tons of steam for 24 hours. See pages 453-454.

What is the I.H.P of the engine, diameter of cylinder 66 inches, length of stroke 3 ft. 6 in., and revolutions per minute 60; the scale being 16 lbs. — 1 inch?

II. And what is the least consumption per I.H.P. per hour which would give 10 lbs. of evaporation for 1 lb. of coal? See Ex. 61, page 454.

EXAMINATION PAPER-No. XV.

FOR FIRST-CLASS ENGINEERS.

I. A ballast donkey discharges a tank in 3 hours alone, and the boiler donkey in 8} hours alone: how long will they take to do it working together? See pages 236-237.

2. A sling chain when lifting a 5 ton weight forms a triangle with two sides of 73 feet, the base is 12 feet, and height of triangle 4'14 feet: what strain is there upon each half of the sling? See Ex. 1, page 411.

3. A packing ring of a cylinder is 73 inches diameter, before being cut was 75 inches: how much must be cut out of the circumference to make it fit the cylinder? See Ex. 39, page 449.

4. The S.S. Candidate left port on the 1st instant on a voyage of 3120 miles with a stock of coals of 800 tons; distances run each day 250, 255, 270, 290, 280, 285, 270, and 265 miles; coals consumed each day 58, 60, 62, 65, 62, 65, 60, and 58 tons.

Make out a tabular statement, and say whether there is a sufficiency of coal to reach her port of destination. See Ex., page 217.

5. A lead wire '072" diameter after testing the brasses is flattened to broad: how many thicknesses will make one inch? See Ex. 47, page 450.

6. For steam above 12 lbs. pressure above the atmosphere, the weight of steam that will escape through an orifice one square inch in area is, in 70 seconds, just equal to the pounds of the gross pressure of steam per square inch: to what breadth of opening must a 6 inch safety-valve rise to allow the escape of 10500 lbs. of steam per hour, the pressure carried being 70 lbs? See Exs. 1-2, page 255,

7. A pair of blocks and ropes are used to hoist a weight of 2 tons, the rope is fastened to the top block, and there are 3 sheaves in each block: what is the strain upon the single of the rope, neglecting friction? See pages 438-439.

8. In the last question, supposing 10 per cent. to be lost at each sheave by friction: what will be the pull at the free end of the rope when raising the weight? See pages 438-439.

9. If the compression of a spring that loads a safety-valve be 2 inches, and the pressure to which the valve is loaded 65 lbs. per square inch: what will be the load per square inch on the valve when it is lifted to give an area of escape equal to of the area of the valve? The face of the valve is flat. The valve is 6 inches diameter. See Exs., page 256.

10.

Work out the following indicator card, and show the point where the steam is cut off, whether the slide-valve is correct or requires alteration, and if the latter, what?

4. Some repairs took 9 men 9 hours per day for 9 days, and cost £20 38. 9d.; if 10 men had been employed for 10 hours per day: how many days would they have taken ? and what would have been the daily pay per man suppose the same total sum were paid for the job? See pages 152-157.

5. A tank 67 ft. long, 23-ft. 6 in. broad, and 4 ft. 5 in. high: how long will it take to pump it out by a double-acting donkey, the diameter of whose piston is 8 in., stroke 11 in., revolutions per minute 71, if 15 per cent. is non-efficient? See Ex. 42, page 450.

6. A condenser door is 5 ft. 10 in. by 4 ft. 9 in.; there are 21 bolts one way and 18 the other: find the number of bolts, and the pitch, if the bolts be 1 in. from the edge of the plate. See Ex. 34, page 448.

7. What is the pressure per square inch, when the temperature is 80° Fahrenheit, and the barometer shows 29 in. ?

Rule.

4907 × h
9057 x t

See Ex. 7, page 396.

8. If the pressure gauge be 50 lbs., and the area of water level in the boiler be 120 square feet: how long would it take to lower it 6 in. through a † in. rivet being blown out of the ash pit? See Ex. 17, page 444.

I

9. If it take 800 lbs. at a leverage of 12 in. to break a stud 1 in. diameter: what force will be necessary to break a ‡ in. stud at a leverage of 18 in. ? See Ex. 1, page 412.

PPP

IO. What is the weight of a cast iron ball of 8 inches diameter, if 257 lbs. be equal to I cubic inch? See Rule LXXXVII, page 191.

II. Diameter of high pressure piston 32 inches, stroke 33 inches, and steam carried for the stroke; there are 1200 cubic feet of steam capacity in boiler: how many strokes will be required to draw off that amount? See Ex. 43, page 450.

12. If 0'4536 kilograms be equal to 1 lb. English, and if you pay £9 108. 4d. for 200 kilograms of tallow: how much will that be per lb. ?

13. Work out the following indicator card, from a compound screw engine, and show whether the slide-valve is correct or requires alteration, and if the latter, what? Also determine the indicated horse-power for each cylinder.

Diagram taken from a compound engine.

Bottom.

Fig. 141.

EXAMINATION PAPER.-No. XVII.

FOR FIRST-CLASS ENGINEERS.

1. V30+ 34 — (3 + 3).

2. What is the radius of a circle whose area is equal to that of a rectangle whose sides are 7963.7 and 674'3? Rule LXXVII, page 185.

3. Five boilers with 4 furnaces in each; there are 2 lengths of bars, and 17 bars in each length, each bar weighing 42 lbs.: what would a full set cost at 7s. 6d. per cwt.?

4. A screw-shaft 26 feet over all and 13 inches in diameter; the coupling flanges are 27 inches diameter and 4 inches thick, there are 6 holes in each coupling 3 inches diameter: what is the weight of the shaft? Sce Ex. 1, page 265.

5. An engine counter has 6 counting wheels, and it stood at 007436 at the commencement of the voyage, and you know that it has gone twice round, it now stands at 'o00624: how many knots has the ship gone, the pitch being 21 feet?

6. A coal bunker is 32 feet at the top, 29 feet in the middle, and 24 feet at the bottom, it is 30 feet long and 20 feet high: how many tons will it hold at 45 cubic feet to the ton ? Ex. 3, page 203.

7. In altering the pitch of a screw-propeller it is found that the mean effective pressure of the indicator diagram is not altered, the product of the pitch by the square of the knots per hour is not altered.

Question.-If the pitch is altered as under, what will be the speed of the vessel, the diagram remaining the same? Ex. 50, page 451.

Old pitch 14 feet, speed 8 knots, new pitch 13 feet.

8. The pressure forcing a slide-valve upon a cylinder face depends a great deal upon the state of the surface; but in a common slide-valve it is never far from equal to the difference between the pressure per square inch in the exhaust passages, calculated for an area equal to the sum of the area of the port in the valve added to the area of the steam port.

Question. The port of the slide-valve is 9 inches by 28 inches, the port of the cylinder 1} inches by 28 inches, the steam gauge showed 36 lbs., and the back pressure is 4 lbs.: find the pressure forcing the slide upon the cylinder. Ex. 28, page 447.

9. There are 3 cross bunkers in a ship, the coals in the centre one do not alter the trim of the ship, but the coals in the other two will, unless properly proportioned between them; the forward bunker is 34 feet from its centre to the centre of the middle one, while the after bunker is 76 feet from the same centre; you have to put 400 tons of coal in these two bunkers so that the ship may keep her trim: how many tons must go in each?

10. A pair of common engines of 180 N.H.P. If 30 circular inches be equal to one N.H.P., what is the diameter of the cylinder?

11. A paddle-wheel which is 30 feet from centre of float makes 20 revolutions per minute, the ship making 15 knots per hour: what is the amount of slip? See page 271.

12. A steamer over the measured mile is 5 minutes 10 seconds with the tide, and 7 minutes 10 seconds against the tide: what was her correct rate of steaming?

13. Work out an indicator card, and show the point where the steam is cut off; whether the slide-valve is correct or requires alteration, and if the latter, what? Also determine the indicated horse-power for the high and low pressure cylinders respectively.