_a._ Rock shafts must be either forged iron, forged steel, or cold
rolled steel. Cast iron is not acceptable. The following are the
minimum diameters acceptable:
500 gallon pump 1-1/2 in.
750 gallon pump 1-3/4 in.
1000 gallon pump 2 in.
1500 gallon pump 2 to 2-1/4 in.
_b._ The rock shaft bearings must be bushed with bronze and the
bushings pinned firmly in place. The length of each of these
non-corrosive bearings must be not less than 4 inches.
_c._ Rock shaft cranks, valve rod heads, valve rod links, and piston
rod spools or crossheads may be wrought iron or steel forgings, or
steel castings. If of a heavy, strong pattern, these parts, with the
exception of valve rod links, may be of semi-steel or cast iron.
_d._ The sectional area of all connections between rock shaft cranks
and valve rod must be such as to give a tensile or compressive strength
substantially equal to that of the valve rod.