The vacuum brake is a braking system used on trains. It was invented in 1877 in the USA, where it enjoyed only a brief period of popularity, primarily on narrow gauge railroads. The system took a greater hold in the United Kingdom, being used there as the primary form of train braking until the 1970s. Vacuum braking is for all practical purposes now a dead technology; it is not in large-scale use anywhere in the world, supplanted in the main by air brakes. For other uses, see Brake (disambiguation). ... For other uses, see Train (disambiguation). ... 1877 was a common year starting on Monday (see link for calendar). ... Narrow-gauge railways are railroads (railways) with track spaced at less than the standard gauge of 4 ft 8 in (1. ... This is the top-level page of WikiProject trains Rail tracks Rail transport refers to the land transport of passengers and goods along railways or railroads. ... Piping diagram from 1920 of a Westinghouse E-T Air Brake system. ...

Overview

Vacuum brakes permit the automatic application of brakes down the length of a train from a simple control in the driver's hand. They are also fail safe, since they default to an applied state using atmospheric pressure; power in the form of vacuum is used to release the brakes, so if vacuum is lost due to malfunction or the train breaking apart, the brakes are automatically applied. Safety engineering is used to assure that a life-critical system behaves as needed even when pieces fail. ...

Vacuum brakes were a big step forward in train safety. Prior to their invention, a train had to rely on the brakes of the locomotive at the front of a train, and mechanical brakes on the cars and guard's van or brake van (UK) or caboose (US) applied by brakemen to stop an entire train. This limited the braking power of the train and meant only short trains could be stopped safely; furthermore, this system required good communication between the locomotive and the brakemen (normally whistle signals from the locomotive). Since the braking effort was applied irregularly along the train, a great strain was put on couplers, risking train breakup. The vacuum brake was considered preferential to the early air brake in railroad applications largely because it was cheaper to install on a steam locomotive. Air brakes required a steam-powered compressor - bulky, noisy, unsightly and using a lot of power, while the vacuum ejector used to generate vacuum was a much simpler device, having no moving parts. Safety engineering is an applied science strongly related to systems engineering. ... A locomotive (from Latin loco motivus) is a railway vehicle that provides the motive power for a train, and has no payload capacity of its own; its sole purpose is to move the train along the tracks. ... Two cupola cabooses, a transfer caboose and a bay window caboose in Ohio. ... Two cupola cabooses, a transfer caboose and a bay window caboose in Ohio. ... Knuckle (AAR Type E) couplers in use. ... Great Western Railway No. ...

Vacuum brakes have now been largely superseded by air brakes which work on a similar principle but use compressed air instead of a vacuum. This allows for more braking power, since the pressure differential between atmospheric pressure and a feasible vacuum is less than that between atmospheric pressure and a realistic brake-pipe pressure. Piping diagram from 1920 of a Westinghouse E-T Air Brake system. ... Compressed air is used to refer to: Pneumatics, the use of pressurized gases to do work, as used in the Air car Breathing gas, often used in scuba diving, also to inflate buoyancy devices Compressed air can also be used for cooling using a vortex tube. ... Look up Vacuum in Wiktionary, the free dictionary. ...

How they work

Each vehicle is fitted with at least one brake cylinder. These are of large diameter, as only the force from atmospheric pressure is used to apply the brakes (see below). They are enclosed in an airtight case (with a gland for the piston rod) and are mounted vertically with the piston rod beneath. Connection to the brakes is by brake rigging. The brakes themselves take the form of cast iron (or, rarely, wooden) blocks which are pivoted to bear on the train wheels. diurnal (daily) rhythm of air pressure in northern Germany (black curve is air pressure) Atmospheric pressure is the pressure above any area in the Earths atmosphere caused by the weight of air. ... A gland is an organ in an animals body that synthesizes a substance for release such as hormones, often into the bloodstream (endocrine gland) or into cavities inside the body or its outer surface (exocrine gland). ... In a piston engine, a piston rod joins a piston to a connecting rod. ... Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). ...

In sequence, the method of operation is: On coupling up the locomotive, air is exhausted from a pipe running the length of the train by a large steam-operated ejector ("making a brake" – UK). Each cylinder is arranged so that this vacuum initially acts equally on both sides of the brake piston. The piston, which is of cast iron, drops under gravity and releases the brakes. The large ejector is then turned off to save steam and a small ejector (or light pump worked from the crosshead) is employed to maintain the vacuum. Look up Vacuum in Wiktionary, the free dictionary. ... A crosshead bearing (or simply crosshead) is used in large reciprocating engines, whether internal combustion engines or steam engines. ...

If air is admitted to the train pipe, either under the control of the driver or because of an equipment failure, a one-way ball valve at each brake cylinder (or sometimes a one-way piston sealing ring, as found in a bicycle pump) prevents it from entering the upper part of the cylinder. The pressure differential (effectively, the air at atmospheric pressure entering the train pipe) closes the valve and forces the piston upwards, thus applying the brake. The airtight case, which is open to the upper chamber, is acting as a “vacuum reservoir” for the upper part of the cylinder, ensuring fail-safe operation. schematic 3 way ball valve A ball valve (like the butterfly valve, one of a family of valves called quarter turn valves) is a valve that opens by turning a handle attached to a ball inside the valve. ...

To release the brake the driver's brake valve is closed and the vacuum restored by either the small or large ejector, as necessary.

To discharge the vacuum under fine control the driver is provided with a graduable brake valve (which usually also incorporates the controls to admit steam to the ejectors) and a vacuum gauge. The running “pressure” is usually in the range of twenty-one to twenty-five inches of mercury (a perfect vacuum is regarded as thirty-one inches of mercury). During braking the driver will watch the gauge to estimate how firmly he/she is applying the brakes – a light application sees the vacuum drop to about fifteen inches and a heavy one to about ten. Of course in an emergency application ("dropping the handle" – UK) the train pipe vacuum can be completely destroyed. During all normal braking, anticipation and careful attention to the pressure is required as, even with the large ejector turned on, it takes some time to restore the vacuum, release the brakes and allow the train to proceed. It is good practice to restore the vacuum slowly when the train is in motion, to avoid releasing the brakes at the front of the train before those at the rear: neglecting this will cause undue strain on the couplings. Bourdon Tube Type Indicator Side Mechanical Side Mechanical Details A pressure or vacuum gauge usually consists of a closed coiled tube (called a Bourdon tube) connected to the chamber or pipe in which pressure is to be sensed. ... Pressure is the application of force to a surface, and the concentration of that force in a given area. ...

Dual brakes

Since vacuum brakes are obsolete on railways there is a need to convert to air brakes. Fortunately, it is possible to fit rolling stock with dual brake pipes, one for vacuum and one for air, and it is also possible subject to space being available to fit the both kinds of brakes to the wagons. Incompatibility is a kind of break of gauge, but a less serious one. Piping diagram from 1920 of a Westinghouse E-T Air Brake system. ... With railways, a break-of-gauge is where a line of one gauge meets a line of a different gauge. ...

Use on road vehicles

Vacuum brakes are not used on road vehicles because a continueous bleed of air is harder to maintain, also, there is not as much room for large diameter cylinders. Steam powered road vehicles tended much smaller, but quicker reacting, boilers to enable more frequent stops. Vacuum braking would cause the water to drop below a safe level.

See also

Brake (railway) Brakes are the devices on railway trains to bring the train to a standstill. ...