Injector Fail-Safe Brake
Objectives
What is it?
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.
Where is it?
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.
Hydraulic Hoses
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.
How Does it Work?
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.
Try It Out
Try it out! Release and engage the brake with the controls.
Be sure to note how spaces develop between the disks and the plates when the brake is released.
Review
What is the purpose of injector fail-safe brakes?
The fail-safe brake is
Checking the Fail-Safe Brake Function
With the injector stopped and the joystick in neutral, read the Injector Brake Release Pressure gauge on the control panel.
It should read zero PSI.
Move the joystick in either direction and increase the maximum injector pressure for the chosen direction.
Injector brake release pressure should now rise to approximately 300 PSI for the mode you've chosen.
Check the brake pressure gauge that is mounted directly on the injector.
This gauge should indicate the same reading as the brake pressure gauge in the control cabin.
If the readings are not the same, check the quick couplers on the injector bulkhead to ensure that they are correctly connected to each other.
Testing the Fail-Safe Brake
1. Ensure that the injector skates are backed off (tubing secured) and are not applying traction to the tubing.
2. Check the brake pressure gauge to make sure that the brake pressure is at zero.
3. Now close the brake isolation valve on the injector.
4. Move the joystick to about half way for either in-hole or out-hole motion.
Now dial up the Max Injector Pressure Adjust valve.
Both the Injector Motor Pressure and the injector brake release pressure should rise, but the chains should not rotate.
If the chains remain stationary, this is an indication that the fail-safe brake is holding.
Caution - Do not exceed 3000 PSI in-hole or out-hole pressure for this test.
5. With this first test complete, return all controls to neutral. Open the isolation valve for the brake.
Now repeat the test steps with the isolation valve open.
This time, when the injector brake release pressure gauge indicates a pressure reading, the injector chains should rotate.
Final Review
The fail-safe brake is meant to prevent injector motor and chain movement when the operator control lever is in neutral or in the event of a failure with the hydraulic system.
It is not intended to bring the injector to a stop during normal operation.
The fail-safe brake is spring applied and released by hydraulic pressure.