The Mechanical Handling and Storing of Material

4oo THE MECHANICAL HANDLING OF MATERIAL installed in suitable barges, the latter being more often used for dredging purposes, as shown in Fig. 563. Fig. 564 illustrates a very usual method of using grabs for unloading barges and depositing the material in railway trucks. Fig. 564. Crane and Grab for Unloading Purposes. Approximate Quantity of Material One Man can Raise with a Priestman Grab per Day of Ten Hours from an Average Depth of 20 Feet. Capacity of Bucket or Grab, in Cwts. Grain, in Quarters. Small Coal, Shingle, etc., in Tons. Coke, in Tons. 3 5 10 1,200 200 125 20 2,400 400 200 30 3,200 550 275 40 4,000 700 350 The Hunt Grab•—Another type of a two-chain grab is the Hunt grab, illustrated in Fig. 565. The principal difference between this and the Priestman grab is that whereas in the Priestman type the jaws are swivelled to the centre of the grab and closed from the outside, in the Hunt grab the jaws are swivelled at the haunches (Hone’s patent) to an A-shaped frame, and are drawn together at the centre, which effects a rather more powerful closing action. Moreover, as the jaws open wider, they can take in a larger quantity of material at each lift. One chain is attached to the drum a on spindle b, and the other chain is fixed to the frame. If the first chain be released and the second chain held tight, the grab opens. The short chains are not attached to a second spindle as in the previous grab, but to the top of the framework, as in the latest Priestman grab. The Mohr & Federhaff Grab. —A two-cable grab is built by Messrs Mohr & Federhaff, Mannheim, Germany, and is illustrated in Figs. 566, 567, and 568. Its action is similar to that of the “ Hunt” grab, with this exception, that the cables which close the