Back pressure brake
The counter-pressure brake is a dynamic brake in steam locomotives , which brakes the locomotive through a combination of several measures by compressing the drive cylinders. With the counter-pressure brake, wear and overheating of the wheel tires and brake pads due to braking can be avoided and a permanently high braking force can be achieved without the risk of fading .
The counter-pressure brake must not be confused with the counter- vapor brake , which only uses the braking effect of a steam engine with round slides and is not approved as an additional braking system.
history
The invention of the counter-pressure brake is usually attributed to Niklaus Riggenbach , which is why it is also called the Riggenbach counter-pressure brake. The braking system was first used in vehicles for the Vitznau-Rigi Railway, which opened in 1871 . However, the same principle was already implemented in 1851 by the Scottish engineer John Haswell , who worked in Vienna , in the Vindobona locomotive for the Semmering Railway .
functionality
In the case of the back pressure brake, to put it simply, the functioning of the steam engine is reversed by letting it compress air like in a piston compressor. Since the steam is expelled through the blowpipe below the chimney after work in the cylinders in the smoke chamber , the cylinders would suck in the exhaust gases contaminated with residues if operated as air compressors without changing the air supply via the blowpipe. To avoid this, the blowpipe is designed to be closable towards the smoke chamber. When using the counter-pressure brake, a separate suction opening is released at the same time as the blowpipe closure for the purpose of supplying clean ambient air. The fresh air intake opening does not have a typical assembly point, but is usually located near the cylinders. In addition, the locomotive driver designs the controls opposite to the actual direction of travel and actuates the outflow throttle valves via the valve boxes. The compressed air escapes through the outflow throttle valves, mostly through a downstream silencer. The throttle valves also serve to regulate the counterpressure so that the pressure in the valve body and the inlet pipes between the regulator and valve body cannot force the regulator open. In the case of Deutsche Reichsbahn locomotives equipped with counter-pressure brakes , the requirement was that the valve box pressure must not exceed 6 bar.
The counter-pressure brake is operated from the driver's cab via a linkage, with a combined control being possible. With it, the counter-pressure brake comes into force automatically as soon as the control shows a negative value, i.e. with the control set to forward, it would actually work in reverse. As soon as the control has reached a negative position, the suction opening and exhaust air line are released.
In order to prevent the cylinders from overheating due to the development of heat during strong compression work, it must be possible to inject (hot) water into the intake air. The amount of water is increased with the degree of compaction (usually directly dependent on the control). Without this water injection, there would be a risk that the oil film in the cylinders would be destroyed by excessively high temperatures.
Properties of locomotives with back pressure brakes
With a counter-pressure brake, it is not only possible to keep a set braking force dependent on the speed; the braking power increases even at higher speeds. In this point it differs from friction brakes, which mostly decrease in their effectiveness when the speed is increased due to fading . The actual braking power is directly related to the speed of the wheel, i.e. the more revolutions the wheel makes in the same time, the more braking power can be applied. The locomotive can therefore be kept in a narrow speed range, despite changing inclines, without necessarily having to change the setting, and is therefore the ideal inertia brake, a brake at which the speed - usually on the incline - is maintained, but should not be reduced.
Today's locomotives have a silencer on the side on which the compressed air leaves the cylinder. The compressed air is usually discharged through the chimney so that the draft for the furnace is retained and the auxiliary blower does not have to be used. The typical steam locomotive exhaust blows also sound when the back pressure brake is active, whereby a difference in pitch and volume compared to the normal exhaust blow can be recognized. The number of exhaust blows per wheel revolution is not changed, however.
Areas of application
Riggenbach counter-pressure brakes were used particularly in steam locomotives that were used on long downhill stretches and in cogwheel train locomotives (e.g. on the Vienna Kahlenbergbahn ). Their presence was essential for operation on steep stretches, since this dynamic brake is the third independent brake required for steam locomotives.
Another area of application of the back pressure brake was found in measurement and testing. A steam locomotive equipped with a counter-pressure brake can be used as a brake locomotive due to the possibility of constant, largely wear-free braking, i.e. it can bring about a defined train load and thus the conditions of a drive in the steady state (a state of motion in which the prime mover only has to repay the motor vehicles to be examined) simulate the driving resistances required work). Some of these steam locomotives were therefore used as brake locomotives in Germany until the mid-1970s, for example the 19 / DR class 19 (Reko) and the 18 314 in the VES-M hall or the 18.3 of the BZA Minden .
literature
- Karl Gölsdorf: Locomotive construction in old Austria: 1837–1918. Slezak publishing house, Vienna 1978, ISBN 3-900134-40-5 .
- Author collective Johannes Schwarze, Werner Deinert, Lothar Frase, Heinz Lange, Oskar Schmidt, Georg Thumstädter, Max Wilke: The steam locomotive. Development, construction, mode of operation, operation and maintenance as well as locomotive damage and its elimination . Reprint of the 2nd edition from 1965 by Transpress Verlag, Stuttgart 1998, ISBN 3-344-70791-4 , p. 733 ff.