Traveling Block Safety Control

Companies have been installing limit switch devices on their drawworks for a number of years, but we still get reports of crown damage and personal injuries resulting from the traveling block hitting the crown.

There are two types of crown safety devices. One is installed on the drawworks cover and is activated by a toggle switch when the drilling line gets to a predetermined point on the drum. The other is attached to the drawworks shaft and is activated when a predetermined number of drawworks shaft revolutions has been counted.

These shaft mounted devices can also be used to set the lowest level that blocks can be lowered or limit the traveling block movement when tools are extended and may be in the path of the blocks.  The purpose of these pneumatic safety devices is to remove the power and apply the brake on the drawworks’ drum at a point that allows sufficient stopping distance to prevent the traveling block from contacting the crown.

What can be done to assure the crown protection device will work when needed?

1. In many cases, the device did not operate because it was not reset after the drilling line had been cut or slipped. Anytime the drilling line is cut we must reset and test the crown safety device.
2. The extension on the activating switch must be in place at all times.
3. The crown safety device is sometimes moved when the collars and bottomhole assembly are brought through the rotary table. Anytime the crown safety device is moved or deactivated to allow the traveling block to be raised above the preset stopping point, a red flag should be attached to the drawworks clutch lever as a warning to the operator.  The driller should take extra special precautions while operating with the protection device deactivated.
4. Each time the crown protection device is tested, reset or readjusted, this information should be entered on the daily drilling report.
5. The safety device must have an air supply to operate. If the main air supply valve to the device is closed, the crown protection device is inoperative and will not work when needed.
6. On toggle type safety devices, some people remove the toggle stem from the toggle valve assembly rather than sliding the toggle valve assembly to one side so the blocks can be raised above the present level.
   If this is done the toggle stem should be placed on the driller’s console and the driller should operate with caution until the safety device is again put in proper operating condition.

7. The crown should be protected with rubber bumper blocks or wood seals. When wood seals are used they should be wrapped with expanded metal and safety cables attached to prevent pieces from falling to the rig floor should they be struck by the blocks. 
8. The crown safety device upper level should be visually checked prior to each trip and when coming on tour at the first connection. It should be function tested by activating the toggle manually.