Anti Two Block (a2b) Switch

Anti Two Block

Cranes are provided with two different configurations of anti two block switches, i.e.

some having only one anti two block switch, and some having two anti two block switches. Correct use of the anti two

block switches must be followed to prevent material damage and serious or even fatal

accidents. The applications under which these anti two block switches are used are described below:

A. Primary Anti Two Block Switch (Mandatory For All Operations)

The Primary (i.e. cab-side) anti two block switch is used in ALL applications (expect

operation of the Berminghammer pile driver system). For single-hoist working (i.e.

normal lifting operations), always use this switch, with the weight and chain installed

correctly around the main hoist cable (if the crane also has a Secondary (i.e. right-side)

anti-two block switch installed, the secondary switch is used only in operation of the

Linkbelt pile driver system).

For single-hoist working with cranes on which a secondary anti two block switch is also installed, the

weight and chain is to be removed from the secondary switch and the by-pass flag

installed. Failure to do this will result in the primary switch being non-functional.

However, if the crane is being used for pile-driving operations, see Paragraph b. below.

B. Secondary Anti Two Block Switch (Pile Driving Applications Only)

Operation of the Linkbelt pile driver system requires the use of a Secondary (i.e. right-

side) anti two block switch, as well as the Primary Switch described in Paragraph a.

above. The Secondary anti two block Switch must be used with the by-pass flag removed and the

weight and chain attached around the auxiliary hoist cable.

ONLY during operation of the Linkbelt pile driver system is the Secondary Switch used,

because Pile-Driving is the only application in which it is permissible to deploy and

operate both hoists simultaneously.

Operation of the Berminghammer pile driver system uses an impact hammer stop,

installed near the top of the lead tower, to physically prevent the impact hammer from

colliding with the boom nose by limiting its vertical travel. This replaces the anti-two

block function of the Load Moment Indicator (LMI) system.

WARNING

The PRIMARY (i.e. cab-side) anti two block switch must be used in ALL

Operations except operation of the Berminghammer pile driver system.

Simultaneous two-hoist working is prohibited in all circumstances other than

operation of the Linkbelt Pile Driver System

*Article from http://www.tpub.com/content/constructioncranes/TM-5-3810-307-10/0776290291.htm*

Bode Technical Services specializes in crane repair of electronic control systems on Terex, Demag, Grove, Liebherr, and Krupp cranes. Bode Technical Services utilizes a global network of crane parts suppliers including PAT-Hirschmann, Load Systems International, Terex-Demag, Grove, and Greer.