In the closed position the two short outer chains KK are wound round the spindle A, whilst the inner chain M hangs loosely in the interior, or lies on the top of the material contained in the grab. The movable portion B is held in position by pawl c. The drum is held by the two pawls dd and the ratchet segments which form part of the drum. In order to discharge the load the two,levers LL are made to touch an obstruction which is suspended from the head of the crane, and is adjustable up or down. As this is in a fixed position, when the grab is being lifted the levers LL are forcing down, by means of two short chains, the pawls dd. The drum R>, which is fixed to the spindle A, is compelled to revolve through the weight of the grab and its load, so that the two small chains KK unwind from the spindle A, whilst the hitherto slack chain M winds itself on to the drum D during the process of opening. As soon as the apparatus has thus been
discharged the main chain begins to lower, when the levers LL, being released from the obstruction, are pulled back into their original position by the springs ss, while the pawls dd hold the drum D in its position, and thus keep the jaws open as the grab plunges into the material to be elevated. If the rope or chain be now further lowered, the part B sinks by its own weight into the opening in the top of the framework, and in so doing the pawl c is pushed to one side and held in that position by another small catch. The hoist chain is now pulled up by the crane, B is now no longer held in position, and as it is pulled out of the framework, pulls with it the chain M and unwinds it from the drum D. The revolutions of the drum, and with it of the spindle A, wind up the
two small chains KK, and pull up the levers TT, thus closing the jaws. As soon as the grab is thus closed, the cljain is lowered once more for a foot or so. B re-enters its former position, and is now again held in place by the pawl c, which has in the meantime been released. As B re-enters the frame, the chain M is released and lies loosely on top of the load as the drum is now fixed, when the grab is ready to be lifted
and swung into position for delivery.