Safety air brake changeover cylinder - prevents contamination of air system by hydraulic oil

摘要

A pneumatic braking system for a heavy vehicle includes a changeover cylinder which prevents oil from the normal high pressure hydraulic circuit entering the air circuit to prevent deterioration of its flexible membranes. Oil in the standard circuit pressurises the annular chamber (30) and forces down the hollow piston (20) against a spring (36), the upper end forming a shaft (25) of smaller diameter and a sliding fit in the passage (15). An annular groove (35) connecting with the axial passage (32) is sealed on one side (34) against oil and on the other (33) against air. A spring (22) loaded valve (20) caps the passage (32) when the piston is forced up by spring (36) on failure of oil pressure. Otherwise, the passage is open and another annular groove (27) connects the air brake system (12) around the piston head (28) to the axial passage. Oil leaking past seal (34) passes via the groove (35) to the passage and to the discharge cap (40). On failure, the air supply (11) is connected via passages (18, 16, 15a) to the braking system (12).