Page 23 - WHITE BOOK

source and mechanism of generation (dirt, dust, iron etc) the ring will be a narrow well defined band. The narrow characteristic of this band shows that the particles are approximately the same size and density. Larger bands (dimensionally thicker) suggest there are a variety of particle types and sizes and they do not deposit on the RPC substrate in such a uniform fashion as a narrow well defined band.
Discolorationofthefluidisobservedusingthebulkfluiditselfasthereference. Althoughbrake fluids may come in a variety of base colors or hues, they should all be homogeneous when spottedontheRPCsubstrate. Ifthereisatwo(ormore)phasediscolorationsduringtheRPC analysis is shows the fluid is either degraded or contaminated.
Given the variety of possible contaminants found in brake fluid the condemning point of the fluid should be any visible phase separation from the base brake fluid when using the RCP protocol. The variables and complexities of brake fluid contamination and degradation analysis are such that field technicians cannot be expected to evaluate the root cause of an abnormal RPC analysis result. However, it is important that the field technician be able to discern whether there is a phase change (non-homogenous characteristic) to the test and make recommendation accordingly.
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