Spring-brake dangers
Page 58
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Reference has been made recently in the technical press to replacement springbrake assemblies which are available to replace the spring section of the Clayton Dewandre spring-brake unit. We manufacture many types of spring brake units to suit the braking requirements of different vehicle models. The springs of these units are designed to provide adequate effort to park the vehicle in accordance with Construction and Use Regulations. This means that not only the maximum load of the spring but the rate of the spring has to be carefully considered to take care of brakes out of adjustment. At the same time as these facts are being met. the stress in the spring has to be kept down to a level which will give acceptable service life.
The piston or diaphragm opposing the spring load has also to be carefully designed to ensure that the spring will not start to apply the brakes before the spring air pressure has dropped to a certain pressure. If this condition is not met, there is a danger of brakes rubbing resulting in glazing of linings, brake fade, etc. The reservoirs on the vehicle are also tailored in size to give a specified number of spring brake applications and releases.
Because of the known difference in efficiency between pistons and standard diaphragms, it is not possible
to obtain diaphragm units which are interchangeable with piston units in relation to all the following features :
1. Braking effort.
2. I-fold-off pressure.
3. Operating volume.
A recent comparison between a diaphragm-type and piston-type unit, both having the same size service diaphragm, showed the spring output of the diaphragm assembly to be only two-thirds of that of the piston assembly.
Our actuators should not be fitted with spring units of alternative manufacture, nor should the complete unit be replaced with an alternative. D. H. BALLARD, Director, Clayton Dewandre Co Ltd, Lincoln.