Publication: The Electrician
THE SLATER-LEWIS INSULATOR.
This insulator may now be regarded as a practical success, having withstood the most severe tests over a period of about four years. It will be seen from the illustration that the usual iron stud is screwed into the insulator instead of being secured by cement. The idea, however, is not exactly new, inasmuch as Mr. Cordeaux patented a similar design some seven or eight years ago, but with the addition of an india rubber washer placed on the shoulder or upper gallery on the iron bolt which supports the cup. This washer or cushion is for the purpose of protecting the porcelain threads from a dead pressure, to allow for expansion and contraction of the sundry parts, and to protect the threads from moisture and consequent rust. This rubber cushion or washer Mr. Lewis dispenses with altogether, employing nothing except the porcelain cup and the iron bolt. This is accomplished through a slight modification in the construction of the parts, and by reason of automatic machinery, which cuts the threads with unerring accuracy—a condition absolutely indispensable for the manufacture of a perfectly satisfactory insulator, because the slightest outward or upward pressure will force off the top of the cup.
The new insulator, Fig. 1, when fixed, is brought down to a solid bearing, and the cup sits perfectly upright in its seat, whereas with the rubber washer a solid bearing is impossible; therefore there is (especially round sharp curves in the line wires) a strong tendency to pull the insulator aside and out of truth with the support, thus throwing great pressure on the porcelain threads, and causing, in many instances, complete fracture. This condition of things grows worse as the rubber deteriorates, and the decay goes on, until finally no rubber whatever remains, and the insulator is left to rock about on the stud to the damage of chafing the wire and ripping the earthenware threads.
The importance of dispensing with the rubber altogether is therefore fully apparent. About 200,000 of these insulators have already been sold to various railway, telegraph, and telephone companies at home and abroad, and repeated orders on a large scale are being constantly received. A large number of these insulators have been under trial on the postal telegraph lines for some years, and a further quantity are now being supplied under contract with the owners of the patent, the Telegraph Manufacturing Company.
The insulator is also supplied with patent self-binding screw tops, by means of which a perfectly rigid attachment is instantly made. The cups can afterwards be renewed or taken down for washing without disturbing either binder or bolt. This is effected by an arrangement of a right-hand screw on the bolt and a left-hand screw on the insulator.
This arrangement is shown in elevation in Fig. 2.