Exhaust or Blast Pipe.-The blast pipe to be of cast iron, the top to be turned and bored to the form shown. Safety Valves.-These are of the kind known as "Ramsbottom's duplex" safety valves. They are fixed on the fire-box casing. The All columns are of brass turned bright, fixed on a cast-iron man-uole cover. The springs were set so as to blow off at 140 lbs. per square inch. the joints were accurately faced, and found to be perfectly steam-tight. 51/5 5916 " DIMENSIONS OF SAFETY VALVES. B V R$V SVS. SECTION. RH Locomotive Boiler Safety Valves. The following figures serve to illustrate an arrangement of safety valve for locomotives and portable land boilers which is more convenient than any known arrangement of dead weights or dead weight and lever. Instead of a weight, the end of the lever is pulled down by a "Salter's" spring balance, and, in order that the ordinary graduations on these balances may serve to indicate the pressure in lbs. per square inch in the boiler, the levers are usually proportioned, as shown in figures, where the length from the centre of the valve to the centre of the fulcrum, or F, is made equal to the diameter of the valve, d, and the total length of the lever, L, is made equal to the diameter of the valve multiplied by the area, A. The weight of the valve and lever being small, and the pressure per square inch great, the former is usually neglected. PLAN. RAMSBOTTOM'S SAFETY VALVE FOR DUBS & Co.'s LoCOMOTIVE. Thus, by our former formula for the lever safety valve— Substituting the above ratios— 12 56 inches.. By thus arranging these proportions, each lb. of pressure of steam per square inch on the valve corresponds to a lb. pull on the "Salter's" spring balance. Generally, locomotives are fitted with two safety valves placed close together, and actuated by one spring and cross bar, as shown. In order that each valve may be subjected to the same downward pull from the spiral spring, Mr. Turnbull has devised a simple arrangement of screw pin, with square ends, as shown in the next figure and in plan at A, whereby the driver may move the spring nearer or further from one of the valves, and thus make certain that both the valves shall blow off simultaneously. A LOCOMOTIVE SAFETY VALVE LECTURE XXVIII.-QUESTIONS. 1. In designing locomotive boilers it is necessary to provide for a sufficiently large amount of heating surface and a sufficiently strong draught. Sketch a section through a locomotive boiler, describing the manner in which these two requisites are provided for. (S. & A. Exam., 1888.) 2. Sketch a section through the entire length of a locomotive boiler, showing the fire-box and smoke box. Mark the positions of the safety valve and regulator valve. 3. Sketch a section through the fire box of a locomotive boiler, showing particularly the method of supporting the flat surfaces, and explain your drawing by an explanatory index of parts. 4. Describe, with sketch and an index of parts, the steam regulator, valve rod and handle, for a locomotive engine. State the conditions essential for the successful working of a regulator valve in a locomotive engine. 5. Sketch and describe a safety valve suited for a locomotive boiler. 6. Sketch and explain a lever safety valve with Salter's balance. How can the readings on the balance which are graduated to lbs. pull on the spring be made to indicate the pressure per square inch of steam in the boiler? 7. Sketch and describe Ramsbottom's safety valve. Sketch also an ordinary safety valve with Salter's spring balance. Mention the respective advantages of each. 8. If the pull of the spring of a locomotive safety-valve lever is 80 lbs., the length from fulcrum to valve being 31", from valve to spring 21", and diameter of valve 3"; what pressure per square inch will the steam have when blowing off! Ans. 79°2 lbs. 9. Describe, with such sketches as you think necessary, the construction and arrangement of parts in either a marine, or stationary, or locomotive engine, whichever you are most familiar with. (S. and A. Exam. 1890.) Io. Sketch a longitudinal section through a modern locomotive boiler showing the smoke box and the method of staying the fire box, and point out briefly the chief improvements now introduced. (S. and A. Exam. 1893.) 11. Describe a form of safety valve such as is frequently used on locomotive boilers where two valves connected by a lever are held down by a spring applied between the valves, showing by sketches the construction of the appliance. (S. and A. Exam. 1893.) 12. Describe, with such sketches as you think necessary, the general construction of a locomotive engine. (S. and A. Exam. 1894.) APPENDIX. QUESTIONS from the Elementary Stage of the Science and Art Department's Examinations in STEAM, from 1890 to 1896, which are not included at the end of the Lectures. To each question a reference is made where the subject is treated. 1. Sketch the Newcomen engine in sectional elevation. During what portion of each stroke, and in what manner, was heat unnecessarily wasted by Newcomen's arrangement? How did Watt propose to lessen the waste of heat, and in what way did he carry out his idea? (S. and A. Exam. 1891.)* 2. State concisely the chief improvements which Watt made in the steam engine, so as to give some idea of the mode in which they were carried out. Sketch in section Watt's single-acting engine, and explain its working. (S. and A. Exam. 1892.) * 3. Describe, with the necessary sketches, the changes introduced by Watt in order to convert an engine in which the steam was employed for lifting a pump-rod, into the modern form of engine as employed for driving the machinery in factories. (S. and A. Exam. 1895.)* 4. What were the chief improvements made by Watt in the atmospheric pumping engine? Draw an approximate indicator diagram of such an engine, before the improvements to which you refer were introduced. (S. and A. Exam. 1894.) * 5. Describe Hornblower's compound or double cylinder engine, and explain by sketches the manner in which the steam passes through the cylinders into the condenser. You can take either the single- or doubleacting engine. (S. and A. Exam. 1890.) * 6. Assuming that the steam in a steam cylinder expands according to Boyle's law, show how to find the terminal pressure for any given boiler pressure and cut-off, and how to find the mean pressure during the stroke. then assuming that the boiler pressure is 100 lbs. absolute per square inch * See Authors Text Book on Steam and Steam Engines. |