Instructor. That is right, and you understand then all it is necessary to do to have the main valve moved down is to have a pressure of steam on top of the reversing piston, and to have it moved up again exhaust this pressure of steam from the top of the reversing piston? Student. Yes, sir; I see that very clearly, but I am just as bad off, for I do not understand how steam is admitted and exhausted from the top of the reversing piston. Instructor.-The admission and exhaust of this steam is accomplished by the reversing valve, 16. The chamber containing this valve is always in communication with the chamber between the pistons of the main valve and, therefore, al'ways contains the same pressure of steam; the port connecting these chambers is not shown in this cut. When the valve is moved down to the position shown in the cut, steam is admitted to the top of the reversing piston, and when it is moved up this port is closed, and the cavity in the valve bridges a port leading to the exhaust and the lower of the two ports leading to the top of the reversing piston and, therefore, when the reversing valve is moved up steam is exhausted from the top of the reversing piston. Is it now clear to you how steam may be admitted and exhausted from the top of the reversing piston? Instructor.-All right, we will start with the main steam piston up and the main valve down, and admit steam to the pump. Student.-When steam is admitted the main valve will be moved up and steam admitted to the upper end of the cylinder, and the main piston will be moved down. As it nears the lower end of the stroke the reversing valve plate strikes the knob on the end of the reversing valve rod and pulls it with the reversing valve down, admitting steam from the reversing valve chamber to the top of the reversing piston, and the main valve is moved down, admitting steam to the lower end of the cylinder, and the main piston will be moved up. Instructor. You did not say what became of the pressure of steam in the upper end of the cylinder and, of course, the piston can not be moved up until that is exhausted. Student. That is exhausted when the main valve is moved down by the upper end of the main valve uncovering the upper series of holes in bushing which forms the exhaust port for the upper end of the cylinder. As I was saying, the main piston will now be moved up; when near the end of its upper stroke the reversing valve plate will strike the shoulder on the reversing valve rod and carry it and the reversing valve up with it, exhausting the steam from the top of the reversing piston, and the main valve will again move up opening the exhaust port Instructor. Well, you may explain if from the lower end of the cylinder and Student. It is, and I think I know how the reversing valve is moved up and down. you can. Student. The reversing valve rod, 17, is connected to the reversing valve and extends down into the steam cylinder. The steam piston rod is hollow for part of its length so that when the steam piston is moved up the reversing valve rod is inside of the steam piston rod. When the main steam piston has nearly completed its upward stroke the reversing valve plate 18 strikes the shoulder on the reversing valve rod and moves it up with it. When it has nearly completed its downward stroke the reversing valve plate strikes the knob on the end of the reversing valve rod and pulls it along down with it. Instructor. That is right, and I think you now understand how steam is admitted to first one end and then the other of the steam cylinder. Student.-Yes, I think I understand it all right, but I would like to explain the movement through once. admitting steam again to the upper end. Instructor.-Very nicely, indeed. I suppose you understand that there is a piston in the air cylinder, as well as in the steam cylinder, and that when the steam piston is moved up and down the air piston is also moved up and down? Student.-I understand that the steam and air pistons are connected by the steam piston rod and when one moves the other must also move. Instructor.-You told me that there are two receiving valves and two discharge valves. Do you know the duty of these valves? Student. I do not understand very clearly about them, but suppose that the receiving valves are check valves to prevent the back flow of air from the cylinder to the atmosphere, and that the discharge valves are check valves to prevent the back flow of air from the main reservoir to the air cylinder. Instructor. That is a very good idea of their duties. As the main piston is moved up air is drawn in by the lower receiving valve, 33, at the same time the air contained in the upper end of the air cylinder is compressed, and forced by the upper discharge valve 30, into the main reservoir. When the piston is moved down air is drawn into the upper end of the air cylinder by the upper receiving valve, 31, and the air contained in the lower end is compressed and forced by the lower discharge valve, 32, into the main reservoir. The pump, you see, is doubleacting, taking in a cylinder full of air, and discharging air, at each up and down movement of the piston. Student. I think I now understand how the pump operates. Are the steam and air cylinders of the same diameter? Instructor. No, the steam cylinder is 8 inches, and the air cylinder is 72 inches. The stroke of both is 94 inches. Student. I understand by that the pump will compress a higher air pressure than there is steam pressure to operate the pump. Instructor. That is true, but you must remember that there is a good lot of friction to be overcome, and that all the pressure of steam is not utilized to compress the air. Student.-I have been told that it is important that the air valves should have a proper lift. Is this important, and if so, what is the proper lift? Instructor.-In order to obtain the best results it is necessary that the air valves have sufficient lift, and not too much. The receiving valves should have 4-32 of an inch lift, and the discharge valves should have 3-32 of an inch lift. Student.-What governs the lift of these valves? Instructor.-The lift of all the valves is determined by the length of the stem. The upper discharge valve stop is the upper valve chamber cap, 29. The lower discharge valve stop is the discharge valve stop 44. The stop for the upper receiving valve is the upper discharge valve, and for the lower receiving valve it is the lower discharge valve. Student.-I am curious to know how much one of these pumps weigh; can you tell me? Instructor. These pumps weigh about 300 pounds. Student. I have not fired an engine with a 9-inch pump, but I know a large number of the engines are equipped with this size of pump, and I would like to understand how it operates; will you explain it next time I come up? Instructor. I will certainly try and do so. (1.) No. 1 has right over No. 2 Mecca to Mirbat. (2.) Extra 37 has right over No. 3 Natal to Ratlam. This order gives the train first named the right over the other train between the points named. If the trains meet at either of the designated points, the first-named train must take the siding, unless the order otherwise prescribes. Under (1), if the second-named train reaches the point last named before the other arrives, it may proceed, keeping clear of the opposing train as many minutes as such train was before required to clear it under the Rules. If the second-named train, before meeting, reaches a point within or beyond the limits named in the order, the conductor must stop the other train where it is met and inform it of his arrival. Under (2), the regular train must not go beyond the point last named until the extra train has arrived. When the extra train has reached the point last named the order is fulfilled. The following modification of this form of order will be applicable for giving a work extra the right over all trains in case of emergency : (1.) TIME ORDERS. will run late to (2.) to will run and late late to etc. (3.) will wait at until for Examples: (1.) No. 1 will run 20 min. late Joppa to Mainz. (2.) No. 1 will run 20 min, late Joppa to Mainz and 15 min. late Mainz to Muscat, etc. (3.) No. 1 will wait at Muscat until 10 a. m. for No. 2. (1) and (2) make the schedule time of the train named, between the stations mentioned, as much later as stated in the order, and any other train receiving the order is required to run with respect to this later time, as before required to run with respect to the regular schedule time. The time in the order should be such as can be easily added to the schedule time. Under (3) the train first named must not pass the designated station before the time given, unless the other train has arrived. The train last named is required to run with respect to the time specified, as before required to run with respect to the regular schedule time of the train first named. For annulling a section: ress of the work may require. The If there are other sections following add: Following sections will change numbers accordingly. The character of a train for which signals are displayed may be stated. Each section affected by the order must have copies, and must arrange signals accordingly. (a.) Work extra 292 will run Berne to Turin and work 7 a. m. until 6 p. m. between Turin and Rome. When an order has been given to "work" between designated points, no other extra shall be authorized to run over that part of the track without provision for passing the work extra. When it is anticipated that a work extra may be where it can not be reached for orders, it may be directed to report for orders at a given time and place, or an order may be given that it shall clear the track for (or protect itself after a certain hour against) a designated extra by adding to (1) the following words: (b.) And will keep clear of (or protect against) Extra 223 south between Antwerp and Brussels after 2:10 p. m. In this case, extra 223 must not pass the northernmost point before 2:10 p. m., at which time the work extra must be out of the way, or protected (as the order may require) between those points. When the movement of an extra over the working limits can not be anticipated by these or other orders to the work extra, an order must be given to such extra, to protect itself against the work extra, in the following form: (c.) Extra 76 will protect against work extra 95 between Lyons and Paris. This may be added to the order to run FORM L. ANNULLING AN ORDER. "Order No. is annulled." If an order which is to be annulled has not been delivered to a train, the annulling order will be addressed to the operator, who will destroy all copies of the order annulled but his own, and write on that: Annulled by Order No. Example: Order No. 10 is annulled. An order which has been annulled must not be reissued under its original number. In the address of an order annulling another order, the train first named must be that to which right was given by the order annulled, and when the order is not transmitted simultaneously to all concerned, it must be first sent to the point will display signals for instead of Examples: (1.) No. 1 will meet No. 2 at Hong Kong instead of Bombay. (2.) No. 1 has right over No. 2 Mecca to Medina instead of Mirbat. (3.) No. 1 will display signals for Eng. 85 Astrakhan to Teheran instead of Cabul. An order which has been superseded must not be reissued under its original number. Rules for Double Track. Time-Tables. D-5. Not more than two times are are given for a train at any station; where one is given, it is, unless otherwise indicated, the leaving time; where two, they are the arriving and the leaving time. Unless otherwise indicated, the time applies to the switch where an inferior train enters the siding; where there is no siding it applies to the place from which fixed signals are operated; where there is neither siding nor fixed signal, it applies to the place where traffic is received cr discharged. Schedule passing stations are indicated by figures in full-faced type. |