The fail-safe brake is a hydraulic brake used to mechanically prevent the injector motors from turning.
This state is usually desired in one of two circumstances;
1. When the operator control lever is in neutral.
2. When the hydraulic system that drives the injector fails.
Usually the fail-safe brake is directly coupled to the hydraulic motor(s) that drives the injector chains.
On some injector models the fail-safe brake will be coupled to the planetary gearbox on the opposite side from the motor.
The fail-safe brake typically only has one hydraulic hose connected.
This single hose will supply the pressurized fluid to release the brake, or bleed away fluid when the brake is applied.
The fail-safe brake is a series of friction plate and disk pairs.
The disks are mounted to the splined shaft that runs through the center of the unit.
The plates are prevented from rotating because they are loosely indexed to the case by a rod.
When the brake is released, all of the disks and plates are allowed a small movement along the shaft axis of the unit.
When the brake is applied, powerful springs on one end of the unit force all pairs of disks and plates together.
Because the disks are on the shaft, and the plates are indexed to the case, the shaft is now prevented from turning.
The brakes will release when pressurized fluid enters here...
...and forces this piston...
...to push against this larger primary plate.
This in turn compresses the set springs allowing the stationary plates and disks to separate, and the brake to release.
The brakes will engage when the fluid pressure is not adequate to move the piston, or when the operator activates the brake.
The springs force all of the stationary plates and brake disks against each other, effectively locking the injector motors.
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