Making the Charging and Cleaning Screws.
These goods can be readily purchased from dealers, with the exception of the charging and cleaning screws. They can be made in any brass foundry. The only difference between the charging and cleaning screws is the size. The charging screw, Fig. 5, should be at least 4 inches in diameter, or large enough to pass the hand through, while the cleaning screw should be 1¼ inches in diameter, or large enough to pass over a 1-inch pipe. A piece of sheet lead is fitted into the cover, as shown at a, to protect the metal from the acid. Soft putty is used for a packing, as shown in Fig. 5.
Fig. 5.—The Charging Screw.
The best, although a more expensive, charging screw is shown in Fig. 6. As will be seen from the cut, it consists of a base, k; cover, d; clamp, e, and screw, f. The base is simply a plain iron or brass ring, 4 inches in diameter, ⅛ inch thick and 1 inch high. The bottom is to be faced smooth, while the top is recessed 3-16 inch deep to receive the sheet lead and packing of putty, as at a. Two nubs, b and b, are cast on opposite sides, as shown, to act as grips for the clamp c. These nubs are ¾ inch long and project out from the body of the base ¼ inch, and are made sufficiently strong to stand the strain of the screw. The cover d is made of the same material as the base, the center being raised, as shown, to give it strength. Cast directly in the center and on the top is the nub e, ⅝ inch high and ⅝ inch in diameter. This is drilled to receive the ⅜-inch screw f. A groove 1-16 inch wide and 1-16 inch deep is cut all around the bottom of the screw, as shown at i. A hole is then drilled through the side of the nub e, and in line with the slot i. A pin can then be driven through the hole and will pass through the slot i, making a swivel joint that will connect the cover and screw together. The screw f is made of ⅜-inch round iron sufficiently long to give an action of about 1 inch. The top at n is filed square to receive a wheel such as is used on a common gate valve. A long thread should then be cut on this screw. The clamp c is made a half circle in shape, so as to clear the cover with ease. It should be ¾ inch wide, flat on the under side, while the top side should have a rib cast on it to prevent springing. The top at g should be reinforced with metal and made heavy enough to stand drilling and tapping to receive the screw f. A wood pattern can be made for these parts, and they can then be molded in any brass or iron foundry. In making the patterns they should be cut down as much as possible, so as to make the finished article as light as is consistent with the strength required. The same directions will answer for the cleaning screw. The hole to receive the sheet lead over the cleaning screw should not be over 1½ inches in diameter, and the rest of the screw should be made in proportion to this hole. The advantage of this screw over others is that it does not wrench the sheet lead in making it up, and, owing to its construction, it is always sure to make a tight joint without straining the generator.
Fig. 6.—The Best Charging Screw.