GB898184A - Crown block for oil well derrick - Google Patents

Abstract

898,184. Pulley blocks; oil well derricks. MOORE CORPORATION, LEE C. July 15, 1960 [Jan. 29, 1960], No. 24712/60. Classes 78 (4) and 78 (5). A crown block for an oil well derrick comprises a frame 12, Fig. 5, one end 16 of which is reckoned as the front, which frame supports a row of parallel sheaves 20 rotatably mounted on a common axis, behind which row is a pair of sheaves 24, 27 placed edge-to-edge and rotatable on parallel axes extending from front to back of the frame. In use the frame 12 is mounted for lateral movement atop the derrick 1, Fig. 1, and a line 8 from the winding drum 9 passes over one of the sheaves 24 or 27 and thence to the travelling block 7 which is connected by a plurality of loops 6 of the line to the row of sheaves 20. For drilling the central well B of a set of three spaced wells A, B, C, the line stringing arrangement is as shown in Fig. 8 ; A or C may be drilled without moving the derrick by appropriate traverse of the crown block and, in order to prevent an oblique pull on the drum 9, the line 8 is either transferred to sheave 27 (for well A) or re-strung in the opposite sense on sheave 24 (for well C). Guide sheaves 31 and 32 serve to prevent the line 8 from slipping from sheave 24 or 27 when the derrick is canted from the vertical. This situation arises if the supporting member 5 (Fig. 1) is displaced about its pivotal connection with the derrick to allow the use of the apparatus as a crane. If this usage is not required, the sheaves 31 and 32 are not necessary and the axis 19 of the sheaves 20 may then be parallel to the axes 23, 26 of the sheaves 24, 27.