The Mechanical Handling and Storing of Material

DISCHARGING BY MEANS OF SKIPS AND GRABS 401 jaws pass over three pulleys before being attached to the frame of the grab to effect a still more powerful closing of the jaws. In two-chain always wound on a second drum of the crane, but is often held by an independent drum and brake in connection with a balance weight, a method devised by Messrs Priestman, which acts as follows :— The cable which opens the grab is attached at the crane end to a drum which is loose on a spindle. Cast together with this drum is a second one of smaller diameter from which a second cable leads over a guide pulley to a balance weight. This weight is held in position between two guides, generally behind the crane house, and is fitted with a safety catch to prevent it from falling in case of the rope breaking. The loose drum is ordinarily provided with a band brake manipulated by a special locking lever. As the drum is thus held fast by the brake and the main cable lowered, the jaws of the grab are opened. By a slight modification, this apparatus may be made to act automatically, in which case the spindle is made to revolve by means of a chain grabs the second cable or chain is not connected to the main drum of the Figs. 566, 567, and 568. Mohr & FederhafFs Grab. 26