An investigation of brake application delays in Australian train brake systems
began with a literature review of pneumatic train braking systems. Data located in the
review gave examples of brake application delays of pre 1990 designs from the U.K.,
India and North America. Information on application delays on later Australian designs
was scarce. Reading of literature has shown a difference between the Australian and
North American control valves in the way the propagation of the pressure reduction rate
in the brake pipe is maintained. Control valves of the North American style allow the
brake pipe air to be connected for a short time to a small cavity or quick service volume
of each valve. The quick service volume is then released to atmosphere. The action of
exhausting a small amount of air from the brake pipe helps to ensure a propagation of an
adequate pressure reduction rate as it travels to the next valve. Australian control valves
rely on the ratio of the volume of brake pipe between control valves and the size of the
quick service volume or bulb to ensure the propagation of an adequate pressure
reduction as it travels to the next valve. The air in a bulb of an Australian valve is not
expelled to atmosphere until a brake release is made.
The research explored possible reductions in application delays by utilizing an
experimental pipe test rack that included 4 control valves and 120 meters of brake pipe.
Experiments with different configurations of exhaust orifices or chokes, valves and
branch pipe lengths that supplied the valves gave a record acquired by data acquisition
of the timing of each valve and the local pressure drop from a valve or each valve for
comparison.
Experiments with exhaust chokes that gave a reduction drop rate in the brake pipe
that approached the minimum required to operate a control valve resulted in instability
of the application operation of the control valve. The quick service volume of different
sizes was included in the experiments to give comparisons in the propagation of the
pressure reduction toward the end of a long train. Further increases into the size of the
bulb of a control valve to enhance the propagation features toward the end of a long
train are discussed. The branch pipe with different diameters from 12 mm to 20 mm and
lengths from 160 mm to 800 mm when fitted to an adaptor pipe bracket were
investigated and results show that larger diameters gave larger gulps in the brake pipe.
Other components that were studied included the pipe bracket that is fitted on some
control valves. The pipe bracket and isolation cock was found to add 282 mm of
additional length to the air path and while not changing the operation of the valve, the
results showed a smaller drop in local pressure in the brake pipe to assist the pressure
reduction rate than shown in valves without pipe brackets.
| Identifer | oai:union.ndltd.org:ADTP/217334 |
| Date | January 2005 |
| Creators | Ripley, Ian, ian.ripley@qr.com.au |
| Publisher | Central Queensland University. Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.library.cqu.edu.au/cqulibrary/disclaimer.htm), Copyright Ian Ripley |
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