| 摘要 |
A hydraulic actuator for a reaction type spot type disc brake is provided with an anti-knock back device. The anti-knock back device comprises a strut and a split ring resiliently clamped about an external cylindrical surface of the strut. The strut is biased by a spring against one component of the actuator, such as a piston or the end wall of a cylinder, and is sealingly guided in the other actuator component, such as a piston. The split ring has limited axial play between a wedging surface and an abutment in said other actuator component to correspond to the desired brake slack. If the brake travel is excessive the abutment slides the split ring along the strut. It is prevented from sliding back in the opposite direction by the camming action of the wedging surface. The spring is overcome at a relatively low pressure to render the anti-knock back device substantially load insensitive.
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