An investigation of brake application delays in Australian train brake systems

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.