« PreviousContinue »
tions inay be secured.
Each separate section of the test has a letter assigned to it, such as A., B., C., etc. Reference to the schedule shows at what time and under what conditions this particular test was made. The comparative test which is made under the same conditions at a later period has the determining letter doubled as AA., BB., CC. Each indicator card is stamped with the date, time, the name of the firm, and this determining letter; all other information in regard to general surrounding conditions, springs, and instrument numbers being kept in a record book, or upon the face of the envelope in which each particular group of cards for any one test is put. For each test the records of all the power influences are made by engineers expert in one particular class of observation. The tabulating and figuring is done mechanically as far as is possible in order to eliminate the personal factor.
DESCRIPTION OF INSTRUMENTS FOR MAKING THE TESTS
The instruments used in making these tests are as follows:
Crosby (Boston) Inside Spring Indicators. For all high and low pressure cylinder work in America, and for low pressure cylinder work in England, Japan, and India.
Crosby Outside Spring Indicators. For all high pressure work in England and Japan.
Maihak (Hamburg) Indicators, having outside springs, for high and low pressure work in Germany, India, Norway, and Russia.
Each indicating staff has an outfit of eight indicators. The Crosby indicators are fitted with Sargent's electro-magnet attachments, and the Maihak instruments with Maihak electromagnets.
Current is furnished for the electro-magnets by dry cells and accumulators in America, and by accumulators for all the others, except the Indian and one German outfit, which have small dynamos.
On every test where it is necessary to use two or more indi
cators the electrical fittings are used, thus enabling indicator diagrams to be taken from all the indicators in service at one time from a central control. This system was not advocated by the committee of the American Society of Mechanical Engineers on engine and boiler tests (Vol. XXIV); but the practice which is necessary in order to conduct the tests given in this paper makes it requisite that such a system be used, otherwise the amount of work and the number of men necessary for each job would greatly increase the cost without improving the efficiency of the test or the accuracy of the results. It is the practice of the engineers making these tests to depend absolutely upon the electrical attachments for the indicators. The great value to be secured from these attachments will not be otherwise discussed at this time.
With most of the outfits, Crosby reducing wheels are used, four to an eight indicator outfit. Phantographs are also sometimes used with the American outfits, while the Continental engineers work with, and sometimes prefer, the flat spring reducing wheels.
In England, Japan and India about fifty per cent. of the engines tested have their own reducing motions. Of these about twenty per cent. must be in some way adjusted or have quadrants fitted before they can be considered accurate, while twenty per cent. can be considered accurate enough without addition, but usually with adjustments. The rest have a gear that is absolutely
In America the percentage of fixed reducing motions is about forty per cent., and possibly one-half require to be fitted with quadrants, while occasionally an engine is found having reducing fittings which are constantly in motion irrespective of whether indicator diagrams are taken or not. It has been found that these fittings are worn, so that they are not accurate enough for careful tests. A reducing motion should never be permanently allowed to run; it should be considered in the same light as the indicator, and should receive the same attention.
In Germany about ten per cent. of the engines have reducing motions which can be attached, these fittings being furnished with the engines. The usual custom is to fit dangerously long bars into the cross-heads and drive directly from a flat spring reduction roll.
Amsler No. 6 Planimeter (Switzerland) used as a standard in every outfit, three planimeters to eight indicators. This planimeter reads directly the mean effective pressure of the card if the diagram is made with a forty pound spring. Working with engine and spring on the metric system the planimeter requires
Tachometers for spindle and shaft speeds are all made by Dr. Horn of Leipzig (Germany).
Tachoscope, an instrument which is a combination of a speed counter and a stop watch, is made by M. Guggenheim, Bale (Switzerland).
Pyrometers, Thermometers, Hygrophants, Hygrometers, Hygrodikes, etc., by Taylor Bros., Rochester, N. Y.; Hohmann and Maurer, London; Casartelli, Manchester, (England); and Dr. Siebert and Kuhn, Cassel, (Germany).
Attached to most of the outfits are adding machines such as the Brunsviga (German) or Burroughs (American) and each department has also from one to five dynamometers of the Emerson pattern for use in securing the power of small machines.
CALIBRATION OF INSTRUMENTS.
All instruments are calibrated and standardised after the best known methods. The element of standardising, however, is not a particular important one as these tests are comparative. The instruments are all marked in such a way and the records are kept, so that the same instruments can be used in the same place for the same sets of observation for the comparative test. Any slight variation which may occur in one instrument, therefore, will not show in the comparative result. Notwithstanding this
fact indicators and speed instruments as well as thermometers, are constantly standardised in order that the results from all the tests may be comparative and of value.
THE TEST REPORTS IN THIS PAPER.
Tables are annexed to each summary of test, showing the maximum and minimum horse power reading of each day's test, the variation in percentage from the average load of the day, and the percentage of variation of each of the two or three days' averages. From a study of these variations it will be seen that the variables, caused by the machines going on and off and by the working of the engine governor in attempting to equalize the speed, average to a very fine degree. It will also be obvious that investigations such as are being described would be quite worthless if made upon any other basis of indicator work, as the variables would either entirely offset the reductions, or act in the opposite way, and would give information very untrustworthy for the following tests. The speeds taken during each test are quite complete, and at least ten readings of the speed of any one item are taken in order to form the average. The speed of the engine is secured by means of a continuous counter, the number of revolutions being recorded every ten or fifteen minutes.
Temperatures and relative humidity are secured at intervals. of from one-half to one hour, and are taken during the day, or day and night, as the conditions seem to require.
Permission to publish the names of mills where tests have been made has, in some instances been withheld, so that all tests will be designated only by number and name of state, or city, and country.