Weld seam opening regulator for cylindrical tank building process

An apparatus for defining a weld seam opening between a lower edge of an existing portion of a cylindrical tank and an upper edge of a band used to form a new portion of the tank, the apparatus comprising:

• a frame;
• first and second wheels rotatably joined to the frame for rotation about respective spaced-apart first and second horizontal axes, wherein each of the wheels comprises:
• (i) a circumferential bearing surface, wherein a first line corresponding to the upper edge of the band is tangent to each of the bearing surfaces;
• and
• (ii) a radial flange extending beyond and flanking said circumferential bearing surface, wherein the flange constitutes a limit to horizontal movement of the band relative to the frame along the axial direction of the wheel;
• a third wheel rotatably joined to the frame for rotation about a third horizontal axis that is laterally between the first and second axes, the third wheel comprising a third circumferential bearing surface with a second line corresponding to the lower edge of the existing portion of the tank being tangent to the third bearing surface and being located above the first line;
• and
• a fourth wheel rotatably joined to the frame for rotation about a vertical axis, the fourth wheel comprising a fourth circumferential bearing surface with a substantially horizontal line being tangent to the fourth bearing surface and being located below the first line, wherein the fourth bearing surface biases the band relative to the frame.