How to Use Altec’s Anti Two-Blocking System
This Altec Sentry short course explains the function, testing and inspection of the Altec anti-two block system (ATB). Note: before using this system, you must complete general training and familiarization for every model of crane you will operate. Read and follow the safety and operating instructions in the operator’s manual and unit instructional placards. Follow all applicable work rules and regulations and use the required personal protective equipment.
Anti two-block or ATB systems help prevent the ball block from contacting the boom tip. This is called two-blocking and can cause injury or death as well as damage to the crane, load line and ball or block. The Altec ATB system consists of a load line weight suspended from a chain, connected to a boom tip ATB switch. The ATB switch connects to the crane’s LMAP system through a wire or battery-powered transmitter.
Two-blocking can occur by:
- Winching up too far
- Booming down
- Extending the boom without paying out enough load line
If this happens, the ATB system triggers an audible alarm and an alert on the LMAP screen. It also disables certain crane functions. Examine and test the ATB system during the pre-operational inspection and whenever it is reinstalled. Check that the cotter pins on the ATB weight and switch are secure and in good condition. The ATB chain has a quick connect link. This allows easy assembly when the crane is reconfigured for certain crane functions such as lifting personnel. During your visual inspection, ensure this quick connect link is fully closed and that the chain is the proper length. If the pins or quick connect link are damaged or inoperable, it could cause the weight to fall while the crane is in use.
To test the ATB system, slowly raise the winch until the ATB weight is lifted. Verify the LMAP anti-two block alarm activates.
Check the following control functions do not operate:
- Winch raise
- Boom lower
- Boom extend
- Rotate (on some units)
The winch lower, boom raise and boom retract functions will operate normally. To complete the test, lower the winch to turn off the alarm and LMAP two-block warning. Verify normal winch and boom functions are restored. If any deficiencies are found, remove the unit from service and contact a qualified mechanic. The anti-two block system is a critical safety component on your Altec crane. Inspecting and testing it helps prevent death, injury, or equipment damage during crane operations.
Visit Altec Sentry’s website to access operator safety and maintenance courses. For questions about Sentry training or to register for a class, email sentrypost@altec.com.