A. No; because the exhausts are not simultaneous; but it must be somewhat larger.

Q. How many nozzle-tips usually come with each engine?

A. Three.

Q. What does it indicate when the exhaust and smoke from an extension-front engine, of the M. M. S. pattern, all pass up to one side, or in front, or back of the stack?

A. A poor steaming engine, with one of the following defects: 1, stack to one side, or front, or back of the exhaust pipe; 2, petticoat-pipe not set in true; 3, exhaust-nozzle not set squarely on the pipe, leaving a shoulder.

Q. Will any other defect cause this side exhaust?

A. Yes; when a petticoat-pipe is used, and that gets out of proper "line."

Q. What is the object of the petticoat-pipe in extension-front locomotives?

A. Its main purpose is to direct the steam jet from the exhaust-nozzle into the smoke stack, and also to make a more continuous pull on the fire.

Q. Can the "pull" on the fire be manipulated to any extent by changing the position of the petticoat-pipe?

A. Yes; the greater the space between bottom of smoke stack and top of pipe, the less continuous the "pull.".

Q. Does the diameter of the pipe cut any figure?

A. The smaller the diameter (within certain limits) the stronger the "pull," because the smaller pipe gives velocity to the escaping matter from the front end, thereby causing the fire to burn more strongly.

Q. How can you tell if the stack, exhaust pipe, and nozzle are all in line with each other?

A. Stand between head-light and stack and hold the end of a stick over the inside, passing it around the top, when the engine is working. If the exhaust strikes the

stick harder on one side than on the other, the stack is out of line, or not filled by the exhaust.

Q. Why not test this by sight from the cab?

A. Because the stack might be out of line front or back, and this would not show.

Q. How can the exhaust stand-pipe be tested for leak?

A. When the steam-pipės are tested with cold-water pressure, close the relief valves and cylinder cocks, plug the nozzle, fill all up with water, and put on the pressure.

Q. What is the best time and way to test the tightness of steam joints?

A. After the engine has been in the house some time, with fire dumped and about 40 pounds of steam, to open out the front end and cool the smoke-box, then give steam with lever in the center and cylinder-cocks shut, and test with a torch on a stick.

Q. What is a common cause of leaky exhaust-pipe joints?

A. Where the nozzle is fitted to the stand-pipe with a flat ground joint and only two studs, there is apt to be an opening at the quarter places between the studs.

Q. What is the remedy?

A. Two more studs.

Q. What is the prevention?

A. Three studs instead of two.

Q. How can a leaky exhaust-pipe joint be tested? A. By plugging the nozzle, opening the angle-cock on rear of tender, closing the cylinder-cocks and reliefvalves, and pumping up air; the torch will show any leak at the joint.

Q. Suppose the air-pump exhaust is not coupled into the main exhaust?

A. Break the joint, red-lead one face; bolt the joint together, and see if complete metal-to-metal contact has been made.

Q. If a gasket be used here, what is the best kind?
A. Soft copper.

Q. What precaution should be taken to prevent the engine from throwing fire?

A. Not to cut off so sharply; to increase the size of the exhaust nozzles.

Q. Give a concrete example of saving effected by changing the exhaust nozzle tip?

A. On a Mikado engine a change of 3/8-inch in the tip

diameter increased the draft so that the fire-box temperature rose 400 degrees. The saving effected was $57,000 a year.

Q. What is the most effective cross section of exhaust nozzle?

A. Rectangular, with the long axis in the axial line of the boiler.

Q. Why is this so?

A. The surface of the exhaust jet, that draws the combustion gases by friction, is about 20 per cent greater than for a circular cross section of the same area.

Q. What is a wing nozzle?

A. One having inwardly projecting radial pins to prevent the whirl of the exhaust and combustion gases. (Figs. 92, 93.)

Q. What is the advantage of radial internally directed projections in an exhaust nozzle?

A. To break up the continuity of the exhaust jet and create a greater front-end vacuum.

Q. What would be a good front-end draft?

A. 15 to 18 inches of water column.

Q. How much would that be measured by a mercury column, such as we find in a barometer?

A. The relation being 13.612 to 1, about 1.1 to 1.31 inches.

Q. What influence has mere nozzle diameter upon the evaporation capacity?

A. Reducing the nozzle from 7 in. diameter to 614 in., the evaporation of one engine was increased from 53,600 actual or 72,500 equivalent pounds per hour to 59,300 actual or 81,900 equivalent pounds, that is, 10.63 per cent. In another instance where a 7-inch nozzle was replaced by a 634-inch and an 8 in. wide deflection plate joint on the edge of the table plate in front of the nozzle there was an increased evaporation of 14 per cent.

CHAPTER XVIII

THE STACK

Q. What is the object of the stack?

A. To make a draft and to remove the hot combustion-gases and cinders to a hight which will enable them to clear the train and other objects near the groundlevel.

Q. What is the object of making it larger at the top than at the bottom, when it is so done?

A. It gives a better passage for the combustion gases, and lessens the distance to which sparks are thrown; thus it helps the draft.

Q. Into what classes may stacks be divided?

A. Into inside and outside.

Q. What is an outside stack?

A. One which does not extend into the smoke-box.

Q. What is an inside stack?

A. One which extends down into the smoke-box.

Q. With a tapered stack, what relation is there between the diameter for best results and the hight? A. The diameter does not vary with the hight.

Q. Is the diameter for a stack affected by the hight of exhaust tip?

A. Yes; the diameter for the best result is greater as the nozzle tip is lowered.

Q. What is the relation between the stack diameter and the front end when the exhaust tip is at the center of the boiler?

A. The smallest stack diameter should be one-quarter as great as the front-end diameter.

Q. What is the relation between the diameter and the hight of the outside stack?