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26 stroke and cutting off once for all with the throttle valve, the boiler has to stand it. It can hardly be said to be detrimental to the boiler, because you cut off just as suddenly with the regular cut-off mechanism as with the . throttle. Mr. Ryan. stated that with a boiler properly braced it will move from %-in. to 3/16-in. in @ 72in. boiler, and this, so far as he knew, would not be detrimental with a regular standard high pressure or slide en- gine, if the boiler was propetly con- structed, and only carrying its rated capacity of steam. If built for 100 lbs. pressure, and carrying 150. lbs., that would be a different proposition. , Mr. Brunner thought it depended upon how fast the boiler will evap- orate water and make steam. The safety valve ought to take care. of the increased pressur¢é, and he did not think it would be detrimental. Mr, Ryan thought that' the great- est detriment to marine boilers in lake practice is the fact that the en-. gineers do not have sufficient time to take care of the boilers when' they are in port. They come into the ore docks, blow off, pour cold water in the boilers, and in five or six hours are going out with steam up. He thought, however, that the safety valve ought to take care of the trou- ble referred to in the question. EXPLOSION OF MARINE BOILERS, Mr. Hartley mentioned the. fact that the majority of violent explo- sions that have taken place in marine boilers have been at the starting of the boilers, not the stopping. A ma- rine engine takes steam with a gulp that relieves the pressure that has been standing on the boiler. Prob- ably the boiler plates have become overheated, decomposition of steam takes place, and as soon as the pres- sure is relieved and the globules have been relieved, the overheated plates cause a volume of steam to rise up more than the safety valve can take care of, and consequently if the boiler is weak an explosion -takes place. The same thing applies to locomotive boilers. Locomotives are liable to be suddenly stopped, and the safety valves must take care of the pressure. Mr. Hartley could not understand the great pulsation of the boilers mentioned. If they were cyl- inder boilers, perfectly round, how could they pulsate, as the pressure is equal on all sides? Conclatiing his remarks, Mr. Hart- ley paid his respects to the steam dome on boilers, which he condemned strongly, in which others present agreed with him. : The MARINE REVIEW The next question was: "Is the Or- dinary Boiler Inspector of the In- surance Companies and the Govern- ment a Hindrance or an Aid to the Boiler Manufacturers?" In reply, Colonel Meier said that the question could not be answered categorically, it depends upon the man. If well posted and honest, he is a help; otherwise, a decided hin- drance. In this there was general "agreement, Mr. Bate stating that in his section of the country general re- liance was paid to the inspector's ad- vice in the matter of specifications, etc., and he did not know how they would get along without the in- spector. : Question 3: "Can any of the mem- bers give from experience of practi- cal testing, best spacing of tubes in high pressure boilers?" In answer to the above, Mr. Rich- ard H. Bate, of Wm- T. Bate & Son, Conshohocken, Pa., read the report of a special committee on this sub- ject 'which was made to the A. B. 'M. A. in 1889, and appeared in their printed proceedings of that year, and is as true now as it was then, viz.: QUESTION OF TUBE SPACING. The question of the tube spacing is largely dependent on the quality of water to be used, and also on the circulation of the water in the boiler. The generally received water circulation is, that there are two currents at work in the boiler. Both have their rise at the bottom, just over the fire. One is a fore and aft circulation; the other an up and down current. The fore and aft cur- rent rises among the tubes carrying the water from the lower front to upper back end. There it falls and sweeps the bottom to the front again. The up and down current rises among the side tubes and falls among the center tubes, the center being colder than the sides. The spacing must be arranged to give as free play to these currents as possible, eo. that when steam is formed on a plate, it may be immediately swept off and taken . the steam space. It appears to necessary to have a large space at the bottom of the boiler so that a sufficient body of water may be main- tained there to prevent burning. There should be a good space be- tween the shell and tubes, and a cen- ter space should be allowed between the tubes for a downward current. The distance of the tubes from each other should be dependent on the quality of water used, but must be enough to allow a free circulation. Our practice is to allow a space be- tween shell and tubes of one-eight- Opinion of. inch. eenth of the diameter of the boiler. This gives 3 in. of space in a 54-in. boiler, and 4 in. in a 72-in. boiler. The center space should be one- fifth of the diameter of the boiler giving 5 in. in a 60-in. and 6 in. in a 72-in. boiler.' This rule is independ- ent of the size of the tubes. Each tube should be one-third of a diameter from every adjoining tube, both horizontally and vertically, but no tube of any size should be hearer than 1 in. to any other. Cne good reason for this minimum is that less distance will not give sufficient strength to the metal be- tween holes to resist the stretch of the expander, in resetting tubes. There should generally be a man- hole below the tubes, especially so with bad water, to facilitate cleaning; also to make sure that there is a sufficient body of water below the tubes. In small boilers, use a small man- hole or a very large handhole. The tubes should be placed higher than threefifths of the diameter from the bottom of shell, except where a dome is used, when they may be carried one row higher. One method of ar- riving at the proper number of tubes in a head is to make their inside area a certain percentage of the area of the head. Sixteen to 18 per cent of the area of the head seems 'to give good results. The ends of tubes should be beaded to aid the tubes in staying the heads. : TESTING OF BOILERS WITH COLD WATER. The fourth question was: "Is the testing of boilers with cold water in- jurious to same?" Colonel Meier in reply said that that depends upon. several circum- stances. If you were testing a boiler at Duluth, where the temperature was 40 below zero, I would advise warm- ing the water a little; and if testing 'in Georgia in the summer time, at 104 in the shade, you would not need to warm the water. Anything can be made very injurious if car- ried to extremes. We recommend in the standard specifications that were adopted by this association that the hydrostatic test shall never, on boil- ers built strictly to the specifications, exceed working pressure by more than one-third of itself and this ex- cess limited to 100 lbs. per square The water used for testing to have a temperature of at least 125° F. The speaker was' asked whether as a practical boiler builder building for his own use he would test with cold water, and replied that he believed he would.