Our Special Study Course THE WESTINGHOUSE AIR BRAKE (PART 2, SECTION 1.) Copyright, 1914, by Brotherhood of Locomotive Firemen and Enginemen. Definitions of Terms Used. 1. Believing it of the greatest importance to the student that he should have a complete understanding of the terms used in air-brake practice, we preface this paper with a few of the many such terms which by custom and long usage have come to be associated with the construction and operation of the air brake, the meaning of which should be thoroughly familiar to everyone studying the subject. Application. The operation of applying the brakes by creating a pressure in the brake cylinder and forcing the brake shoes against the wheels. Graduated Application.-An application of the brakes in which the brakecylinder pressure is increased in a series of steps or graduations. Service Application.-A gradual smooth application of the brakes such as is made in an ordinary stop or slow down; so called because it is the usual application in ordinary service. Full-Service Application. The most powerful service application of the brakes that can be obtained. Partial Application.-Any service application of the brakes less than a FullService Application. Emergency Application.-The quickest and most powerful application of the brakes that can be made, in order to stop in the shortest possible distance and avoid a collision or save life. Reduction. The lowering of the air pressure in the brake pipe below that usually carried in order to cause an application of the brakes. A specified amount is generally referred to, as, for example, "a ten-pound reduction," "a service reduction of fifteen pounds," etc. Service Reduction.-A moderate gradual reduction of brake-pipe pressure to cause a service application of the brakes. Full-Service Reduction.-A service reduction which causes a full-service application of the brakes. Over Reduction. Any service reduction which is greater than a Full-Service Reduction. Emergency Reduction.-A sudden rapid reduction of brake-pipe pressure to cause an emergency application of the brakes. Release. The operation of releasing the brakes by discharging the pressure from the brake cylinder and pulling the brake shoes away from the wheels. Graduated Release.-A release of the brakes in which the brake cylinder pressure is reduced in a series of steps or graduations instead of being completely discharged at one time. (A characteristic of the newer types of passenger triple valves only.) Charging. Building up the pressure, in that part of the air-brake system which is normally under pressure, to the proper amount that is specified for that particular system. Recharging. The term used to designate the charging up during the release after an application. Lap. Generally speaking, this term means the closing or blanking of an opening or passage; in connection with the air brake it is used to designate the preventing of any change of pressures in the various parts of the system as far as such change is controlled by operating valves or devices. Mostly it refers to a certain position of a valve in which the connection between all different pressures is closed. Quick-Action.-That effect of the operation of a triple valve which causes an emergency application to pass rapidly from car to car throughout the train, by causing a local reduction at each triple valve. Equalized Pressure, or Pressure of Equalization. That pressure at which two volumes, originally at different pressures, will become equal if they are connected together and allowed to remain connected. Port. The name usually given to the machined holes in a valve or valve seat, placed so as to control the flow of air from one volume to another when the valve is in different positions on the seat. Register. When a port in a valve comes directly over a port in the valve seat making the connection between them fully open, one port is said to register with the other. If either port is not fully open, they are said to partially register. Braking Power.-As generally used, this term expresses the relation be tween the total pressure of all the brake shoes against the wheels, and the total weight of the car on the rails. It is expressed by dividing the total brake-shoe pressure by the total weight of car and giving the result in per cent. For example, if the total brake-shoe pressure is 25,000 pounds, and the total weight of car is 50,000 pounds, the former divided by the latter gives 1⁄2, which is 50 per cent braking power. Retarding Force. The actual frictional force between the brake shoe and the wheel, which tends to reduce the speed of the moving car or locomotive. Piston Travel.-The actual distance, measured on the piston rod, through which the brake-cylinder piston is forced during an application of the brakes. Standing Travel.—The piston travel that results from a brake application when the car is not moving. Running Travel-The piston travel that occurs in a brake application when the car is in motion, running over the road. It is greater than the standing travel because the motion of the car and the unevenness of the track allow all loose journals and joints to take up more lost motion than when the car is standing. False Travel.-A rather indefinite term often heard in connection with airbrake matters, sometimes referring to the difference between standing and running travel, and sometimes to an extra excessive travel momentarily caused by some unusual temporary strain. It is unnecessary in the description of air-brake operation, and therefore not used in this course. Foundation Brake Gear.This term has already been described as the system of rods, levers, supports, brake beams, hangers, etc., which serve to connect the piston rod of the brake cylinder with the brake shoes, to transmit and multiply the pressure obtained in the cylinder to the shoes. Automatic Devices.-The term automatic means "self-operating." As already stated, the automatic air-brake devices are self-operating, due to changes in air pressure in parts of the system. A Manual Device is one operated by hand, that is, not automatic. It should be noted that, although the automatic air-brake devices are set into operation by changes in pressure in parts of the system, these changes in pressure are most generally produced by a manual device, such as the brake valve, conductor's valve, angle cock, etc. The Manipulation of the Brake is the term used to cover the handling of the manual devices so as to cause the automatic devices to operate. Regarding Illustrations. A Diagram, or Diagrammatic View, of an equipment or device is a drawing in which the arrangement of parts and connections is made as simply as possible without regard to the actual shape and design of the device or its real position on the car or locomotive. By its use, the operation and sequence of parts are more easily understood than if a true drawing was used. A Plan View is one in which the observer is supposed to be looking down onto the top of the device from above. A Side Elevation is a view of the device looking at one side. A Section is a drawing in which a part of the device is cut away so as to show the interior parts, cavities, chambers and passages. Where the section passes through solid parts, the thickness and position of such parts are shown by section lines drawn parallel to each other and rather close together. These section lines usually indicate the material used; for example, full light section lines all alike indicate cast iron; alternate full line and dotted line indicate brass; wood is shown by waving lines made to imitate the grain of the wood; a light full line followed by a heavy full line denotes steel; a section through leather is shown by heavy and light dots irregularly placed; babbit metal is shown by light lines "criscrossed," etc. Where no section lines are placed it indicates an open place, such as a chamber, passage or port, or possibly a valve, piston or bolt located in that space. Often the chambers, ports and passages are colored to indicate the pressure carried in them. A section may be made from any point of view as most convenient to illustrate what it is desired to show. It is usually stated through what part of the device the section is made. A Central Section is one made along a center line with the half toward the observer cut away. Assembly Drawing.-A section of a device which shows all of the parts assembled in their proper position. Detail Drawing.-One which shows each part or detail of a device separately by itself. Note.-Dotted lines (other than sections lines) are used in drawings to show some part of the device which is hidden by other parts, and would therefore ordinarily not be seen from the point of view taken. The Standard Quick-Action Automatic Brake- OPERATING PARTS. The Triple Valve. 2. Its Purpose.-As has already been explained, the triple valve is a device located on each vehicle in the train, which controls the flow of air between the brake pipe, auxiliary reservoir, brake cylinder, and atmosphere for the purpose of charging the auxiliary reservoirs and applying and releasing the brakes. Two kinds of triple valves are used with the Standard Quick-Action Automatic Brake, namely, the Plain Triple Valve and the Quick-Action Triple Valve, the former being used on engines and freight and switch-engine tenders, the latter on passenger-engine tenders and all cars. As has been mentioned, the operation of the Quick-Action Triple Valve is similar to that of the Plain Triple Valve, except that in emergency it vents a portion of the air contained in the brake pipe direct to the brake cylinder, thus increasing the pressure obtained in the brake cylinders on an emergency application above the maximum which can be obtained by an ordinary service application, and also transmits the quick action serially and rapidly from car to car throughout the entire train. On the engine the brake-pipe reduction is very rapid, when an emergency appliction is made, because the air can flow directly through a large opening in the brake valve to the atmosphere. There is, therefore, no need for a quick-action triple valve on the engine to increase the rate of brake-pipe reduction, because it is already rapid enough. Moreover, if a quick-action triple valve were located on the engine, it would be so close to the brake valve that the fall in brake-pipe pressure when a service application of the brake is commenced (which is, of course, more rapid near the brake valve than farther back in the train) would be very apt to cause it to operate in quick action when not intended and so cause what is called "undesired quick action," that is, undesired emergency application of the brakes on the whole train. For the same reason many railroads consider it unnecessary or undesira ble to use a quick-action triple valve on the tender, while others prefer to put a quick-action triple valve on the tender and risk the chance of obtaining undesired quick action once in a great while rather than put a plain triple valve on the tender and not be as certain to transmit quick action to the train when wanted. As the construction and operation of the plain and quickaction triple valves are practically the same, except for the quick-action feature, we will first take up the Plain Triple Valve. The Plain Triple Valve. 3. The Plain Triple Valve, Figs. 5, 6, 7, 8, 9, and 10, has a cast-iron body with pipe connections to the brake pipe, B.P.; to the auxiliary reservoir, R; to the brake cylinder, C; and an outlet to the atmosphere, usually called the "exhaust," shown by the circle p. The operating parts consist of a slide valve marked 6, in which the graduating valve 7 moves, the piston marked 5 on the stem (piston and stem being one piece), and the graduating stem 8, with its spring 9. The graduating valve is attached to the stem of piston 5 by a pin, as shown by dotted lines. The names of the other parts of the plain triple valve are: body, 2; cylinder cap, 3; cap nut, 4; graduating stem nut, 10; gasket, 11; piston packing ring, 12; bolt and nut, 13; slide-valve spring, 14. The triple-valve piston forms a movable partition between the upper chamber m, above the slide valve, which is connected to the auxiliary reservoir, and lower chamber h, which is connected to the brake pipe. The packing ring, 12, is carefully fitted in the piston to form an air-tight joint with the piston bushing to prevent leakage of air from one side to the other as much as possible. By changing the pressure in either of these chambers, the piston, together with slide valve and graduating valve, can be made to move upward or downward. In release and charging position, the pressure entering from the brake pipe pushes the piston upward as far as it will go, and this is the position of the operating parts shown in Fig. 7. Air can then flow from the chamber h below the piston to the chamber m above it, and to the auxiliary reservoir through feed grooves i in the piston bushing and k in the piston, |