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FINAL TRIALS.

The final trials of the Colorado were held on March 4 to 7 and August 8 and 9, 1924.

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Average S. H. P., calculated...

29,439

29,171

18,953

8567

2541

Total oil, pounds per hour, at 19,500 B. T. U.

30,376.3

29,759.4

20,889.2

10,508.8

4791

Oil per S. H. P., pounds per hour..

1.032

1.02

I.102

1.226

1.894

Oil per square foot heating surface, pounds per hour..

.727

.712

.500

.503

.306

Oil per knot, pounds....

1469.6

1447.4

1135.2

734.4

Water consumption. Main engines. No auxiliary exhaust...

10.835

10.732

11.079

11.369

501.7 13.162

Number of boilers in use........

8

8

8

4

3

Steam at boilers. Gauge..

272.4

273.1

277.5

273.I

267.8

Steam at turbines. Gauge.....

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Steam at turbines. Temperature, degrees F.

451.9

452.9

449.8

446.5

440.9

Superheat, degrees F.

46.3

46.5

38.0

36.1

30.6

Vacuum, inches..

.........

28.46

28.36

29.08

29.00

29.14

Fireroom pressure of water, inches..

6.59

6.81

4.77

4.95

2.43

Shaft revolutions, per minute.

170.10

169.04

149.11

114.43

75.88

Injection temperature, degrees F.

56.2

60.3

39.2

41.3

41.0

Overboard temperature, degrees F.

73.7

76.9

50.9

50.5

42.6

Kilowatts, forward

12,825

12,550

7412.5

6881.2

2250.0

Kilowatts, aft.......

11,709

11,650

8050.0

not used

not used

Total kilowatts..

24,534

24,200

15,462.5

6881.2

R. P. M., main generators (forward).

2019

2000

1758.1

1375

2250 1371.9

R. P. M., main generators (aft).

2041

2028.1

1800.0

not used

not used

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FACTORS IN DESIGN OF FUEL MEASURING
PUMPS FOR DIESEL ENGINES.

BY LIEUTENANT (J.G.) J. E. CANOOSE, U. S. NAVY, MEMBER, NAVY YARD, NEW YORK.

Vacuum generation within the fuel pump cylinder, governor action, and valve design were referred to in a general way in a paper on fuel measuring pumps in the November, 1924, issue of this Journal.

Due to space limitations these factors could not be discussed in detail. This paper will deal more specifically with the following factors:

(a) Generation of vacuum in fuel pump cylinders.

(b) Possibilities of supercharging fuel pump suction. (c) Pressures to be considered in designing, as shown by fuel pump cylinder indicator cards..

(d) The blow-down effect in discharge valves. (e) Residual oil effect on governor action.

(f) The effect of design on tappet clearance variation effects.

(g) Practical design factors to be considered.

GENERATION OF VACUUM IN FUEL PUMP CYLINDERS.

In the previous article mentioned above, it was stated that a vacuum of about 24 inches was generated in the Bureau type pump to open the suction valve automatically. This figure was based on the calculation shown in Figure 1. The 2 pounds initial compression shown by the spring diagram was obtained by testing several springs in a very sensitive machine. The initial compression pressures for the springs

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tested varied from 1 pound 8 ounces to 2 pounds 2 ounces the average being 2 pounds. It will be noticed that the valve has on its under side a threaded boss which engages the spring. This boss reduces the number of free coils, making the springs correspondingly stiffer. However the spring coils do not hug the valve, tightly enough to seriously restrict their freedom in their initial compression condition. This is the point to be considered in reference to vacuum.

In designs where the suction valve functions automatically, the degree of vacuum generated depends primarily on the plunger acceleration and on the relative effective inlet valve area as compared with the plunger displacement. The duration of vacuum (of higher degree) generation is governed by the point of mechanical opening of the suction valve. In other designs, where the suction valve does not function automatically, a perfect vacuum is generated during the first part of the suction stroke at all powers. This assumes no air leaks, no entrained air in the oil, and that in a perfect vacuum the oil remains fluid.

The magnitude of a vacuum determines the rate of air leak past the plunger packing gland. The duration of vacuum coupled with the rate of flow determines the total amount of air taken into the oil. This air destroys the metering function of the fuel pump.

Figure 2 shows cards taken on the Bureau type pump which verify the vacuum calculations given in the preceding paragraphs. In this Figure the card shown at (W) was taken with a very sensitive spring which recorded some peculiar actions. It is apparent that at point "a" the maximum vacuum was generated, with an immediate sharp reduction. The high initial vacuum point is possibly partially due to suction valve friction and inertia, but in greater degree due to high plunger acceleration at this point. The immediate drop is no doubt due to the action of suction pressure on the added area when the valve opened, thus throwing it wider open. An unbalanced

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