Patent ID: 7448312

Claim:
A hydraulic swivel drive for a grab which has two tong-like moveable grab arms, said hydraulic swivel drive having two swivel shafts ( 8 , 9 ) which are pivotally supported in a shell carrier ( 1 ), parallel to one another and whose shaft ends ( 10 ) can be connected to the grab arms, a shaft drive piece ( 12 ), which comprises a plurality of recesses ( 17 , 18 ), is displaceably supported parallel to the swivel shafts ( 8 , 9 ) and in screw engagement with both swivel shafts ( 8 , 9 ) such that the swivel shafts ( 8 , 9 ) are rotated in opposite directions by displacement of the shaft drive piece ( 12 ), and a plurality of hydraulically driven plunger pistons ( 15 , 16 ) provided in a respective recess ( 17 , 18 ) and fixedly supported with the shell carrier ( 1 ,) said recess ( 17 , 18 ) together with an end face of said pistons ( 15 , 16 ), define a plurality of pressure chambers ( 19 , 20 ) arranged to be charged with pressure fluid to displace the shaft drive piece ( 12 ) relative to said pistons ( 15 , 16 ), and wherein the shaft drive piece ( 12 ) defines a fluid pressure supply bore configured to collectively supply the pressure fluid to the plurality of pressure chambers ( 19 , 20 ).