the fuel oil sprayed into the furnace, the ratio of the former to the latter gives us the efficiency of the boiler as set forth in the chapter on Heat Balance.

In central station practice on the Pacific Coast the gross boiler efficiency in the best installations ranges from 81 to 83 per cent. under test conditions. The atomization of the steam lowers this efficiency by about 2 per cent., thus making the best net boiler efficiencies range between 79 and 81 per cent.

The Overload Test. The sudden demand for power during certain hours of the day make an elasticity in boiler steaming qualities absolutely imperative. Otherwise, a great additional expense would be involved in the cost and installation of additional steaming units. Hence the overload steaming qualities of a boiler are of utmost importance, especially in central station or steam auxiliary practice.

As an instance of performance of a boiler under overload conditions on the Pacific Coast, an authentic case is on record where a boiler of 773 rated horsepower developed an overload of 75.7 per cent. for 5 hours and still maintained a gross efficiency of 80.62 per cent.

The Quick Steaming Test.-In other instances the ability of a boiler to hastily get into action is of prime importance. This is especially true in cases where boilers are held in readiness for pumping station operation for fire protection. In San Francisco, California, for instance, is located a high-pressure water system whereby pumps stand eternally ready to deliver 12,000 gal. of water per minute to a height of 700 ft. should disaster by fire ever again visit that municipality. The boilers that operate the pumping station have by test demonstrated that full boiler pressure and steaming conditions can be accomplished in less than thirty minutes time.

Again, other features of test are under special cases desirable to attain. But the two most important tests are those of ascertaining the conversion ratio of heat represented in the steam to the heat supplied by the furnace under normal conditions of operation and under certain definite overload guarantees-in a word, the ascertaining of boiler efficiency for normal rating and for conditions of overload.

Observations Necessary.-A complete tabulated list for final test computation is set forth in the book of instructions previously mentioned as approved or advised by the American Society

of Mechanical Engineers. Let us now look into some of the details necessary to obtain this recorded data.

In the first place, one should note on a log sheet the general observations such as date of test, duration of test, type of oil burner, make of oil burner, number of burners used, and with this information should be compiled sufficient physical dimensions of the boiler to enable one to compute the builder's rating both for the boiler and for the superheater. An illustration of this computation was set forth under the chapter on Rating of Boilers. During the test period, observations are usually taken every fifteen minutes, simultaneously if possible.

Pressure Readings. The pressure of the atmosphere is read in inches of mercury and the steam gauge readings of the boiler and superheater having been duly calibrated or corrected for mechanical inaccuracies, are then reduced to absolute pressure readings as set forth in the chapter on pressures.

The pressure of the oil under which it is forced into the furnace is also usually noted, although it has no bearing on data computation.

The pressure of the draft at various parts of the ash pit, furnace, breeching, and chimney are also noted by means of a multiple cock arrangement shown in Fig. 122. This arrangement makes possible the quick ascertaining of various draft readings by means of one instrument.

The pressure of the saturated steam and also that of the superheated steam is ascertained by inserting carefully calibrated steam gages, the one in the saturated steam compartment and the other in the superheater compartment. These pressures are then converted into absolute pressure readings by correcting for atmospheric pressure as set forth in Chapter III.

Temperature Readings. A thermometer is usually located in the atmosphere without to ascertain general external temperature conditions of the day. One is also placed in the boiler room to ascertain the temperature of the entering air passing into the furnace.

To ascertain the temperature of entering feed waster and fuel oil, thermometer wells with thermometers are also installed at nearby points of entrance.

It is often desirable to ascertain the temperature of the furnace gases at various points in their journey. To accomplish this thermo-couples are installed at the points desired previous to

the firing of the boilers and during the test an electrical pyrometer is advised, especially if other high temperatures are to be taken in various points of flue gas passage.

The Flue Gas Analysis. Simultaneously with the taking of the temperatures, pressure and other readings of the test, the flue gas analysis is ascertained at frequent intervals. The detailed method of taking these data has been fully set forth in previous chapters and methods of computation of combustion data explained. The Heat Balance will be set forth in full in a later chapter.

The Test as a Whole.-The reader has now before him the taking of the test as a whole. At this point he should carefully review all the previous chapters alluded to in this discussion so as to weld into a solid chain the links that go to make up the boiler test in fuel oil practice.

Having thus in mind a complete idea of the various details involved in the taking of the boiler test data, we are now in position to link together the computed data involved in formulating the engineer's report of the economic results of the test.

CHAPTER XXXII

PRELIMINARY TABULATION AND CALCULATION OF

TEST DATA

FIG. 192.

THE systematic construction of a log sheet that will show in the minutest detail every incident in the progress of the boiler test is of prime importance. It is far better to overdo then to underdo in the gathering of detail data of this kind. The notation of remarks from time to time upon the log sheet concerning relevant observations during the progress of the test is of much service to the engineer when he finally comes to decide fine points in economic boiler performance.

No straight and narrow schedule or log sheet can be set forth to meet all types of boiler test. Each particular test as a rule involves its own particular tabulation. Let us, however, consider a series of tabulation sheets for boiler tests in which oil is used as a fuel. The suggestions that will be set forth illustrate a carefully evolutionized scheme of tabulation for such data that may be well followed in guiding one in the construction of his own individual log form should occasion arise.

The Log Sheet for Weighing the Water.-In the previous chapter we have seen that the water is brought to a definite height in the supply tank the instant of starting the test. Above this supply tank are located standardized scales upon which the water is weighed before emptying into the supply tank below. As a rule, at the closing of each hourly period, water readings are computed in order that the engineer may get a preliminary idea of the progress of the test. Blank sheets are given each water

weigher, one to be used for each hourly period. Each sheet sets forth general information indicating the kind of boiler under test, the date of test, the name of the observer, and the particular tank at which each is stationed. A column is devoted to the number of the scale reading, a second to the gross weight of the water and tank before emptying into the tank below, the tare to be subtracted from the gross weight, which is the weight of the upper tank after the water is emptied into the tank below, and a fourth column setting forth the net weight or difference of the two preceding columns. This sheet will have somewhat the following appearance.

By using the type of log sheet above indicated, it is evident that the engineer has a check on his water computation, for in the line marked "total" the footing for the gross weight should exactly equal that for the sum of the tare weight and the net weight.