Fig. 5.
d. The valve and stem of cushion valve must be in one piece without any swivel joint.
Swivel joints are apt to come apart and make it impossible to operate the valve.
20. Piston Rods.
a. Piston rods for their entire length must be of solid Tobin Bronze, and the distinguishing brand of the manufacturers of this metal must be visible on at least one end of each rod.
b. The sizes must be not less than in table below.
| Size of Pump. | 500 gal. | 750 gal. | 1,000 gal. | 1,500 gal. |
|---|---|---|---|---|
| Diameter of rod | 2 inch. | 21⁄4 inch. | 23⁄8 inch. | 21⁄2 inch. |
c. The size and form of connection of rod to piston plunger and cross-head must be such that the stress in pounds per square inch at bottom of screw thread, or at such other point of reduced area as receives the highest tensile strain, shall not exceed 8,000 lbs. per square inch, when the steam pressure acting on the piston is 80 lbs. per square inch.
d. Piston rod nuts, in both steam and water ends, must be tightly fitted, and preferably of a finer thread than the United States Standard. This is to avoid as much as possible the unnecessary weakening of the rod at the bottom of the thread, and to reduce the tendency of the nut to work loose.