In all important tests, a sample of coal should be selected for chemical analysis.
5. Establish the correctness of all apparatus used in the test for weighing and measuring. These are: 1. Scales for weighing coal, ashes, and water. 2. Tanks or water-meters for measuring water. Water-meters, as a rule, should only be used as a check on other measurements. For accurate work the water should be weighed or measured in a tank. 3. Thermometers and pyrometers for taking temperatures of air, steam, feed-water, waste gases, etc. 4. Pressuregauges, draft-gauges, etc.
6. Before beginning a test, the boiler and chimney should be thoroughly heated to their usual working temperature. If the boiler is new, it should be in continuous use at least a week before testing, so as to dry the mortar thoroughly and heat the walls.
7. Before beginning a test, the boiler and connections should be free from leaks; and all water connections, including blow and extra feed-pipes, should be disconnected or stopped with blank flanges, except the particular pipe through which water is to be fed to the boiler during the trial. In locations where the reliability of the power is so important that an extra feed-pipe must be kept in position, and in general when, for any other reason, water-pipes other than the feedpipes cannot be disconnected, such pipes may be drilled so as to leave openings in their lower sides, which should be kept open throughout the test as a means of detecting leaks or accidental or unauthorized opening of valves. During the test the blow-off pipe should remain exposed.
If an injector is used it must receive steam directly from the boiler being tested, and not from a steam-pipe or from any other boiler.
See that the steam pipe is so arranged that water of condensation cannot run back into the boiler. If the steam pipe has such an inclination that the water of condensation from any portion of the steampipe system may run back into the boiler, it must be trapped so as to prevent this water getting into the boiler without being measured.
S. A test should last at least ten hours of continuous running, and twenty-four hours whenever practicable.
9. The conditions of the boiler and furnace in all respects should be, as nearly as possible, the same at the end as at the beginning of the test. The steam pressure should be the same, the water-level the same, the Are upon the grates should be the same in quantity and condition, and the walls, flues, etc., should be of the same temperature.
To secure as near an approximation to exact uniformity as possible in conditions of the fire and in temperatures of the walls and flues, the following method of starting and stopping a test should be adopted.
10. Standard Method. Steam being raised to the working pressure, remove rapidly all the firefrom the grate, close the damper, clean the ash-pit, and as quickly as possible start a new fire with weighed wood and coal, noting the time of starting the test and the height of the water-level while the water is in a quiescent state, just before lighting the fire.
At the end of the test, remove the whole fire, clean the grates and ash-pit, and note the water-level when the water is in a quiescent state; record the time of hauling the fire as the end of the test. The water-level should be as nearly as possible the same as at the beginning of the test. If it is not the same, a correction should be made by computation, and not by operating pump after test is completed. It wil generally be necessary for a time to regulate the discharge of steam from the boiler tested, by means of the stop-valve, while fires are being hauled at the beginning and at the end of the test, in order to keep the steam pressure in the boiler at those times up to the average (luring the test.
11. Alternate Method.Instead of the Standard method above described, the following may be employed where local conditions render it necessary: At the regular time for slicing and cleaning fires, have them burned rather low, as is usual before cleaning, and then thoroughly cleaned; note the amount of coal left on the grate as nearly as it can be estimated; note the pressure of steam and the height of the waterlevel—which should be at the medium height to be carried throughout the test—at the same time; and note this time as the time of starting the test. Fresh coal, which has been weighed, should now be fired. The ash-pits should be thoroughly cleaned at once after starting. Before the end of the test the fires should be burned low, just as before the start, and the fires cleaned in such a manner as to leave the same amount of fire, and in the same condition, on the grates as at the start. The water-level and steam pressure should be brought to the same point as at the start, and the time of the ending of the test should be noted just before fresh coal is fired.