Two kinds of motion at the joints must be provided for, one longitudinal and one rotary, and the experiments seem to show that, while the exterior form of the joints may be the same for both kinds of motion, the interior construction must differ for each, it being inadvisable as well as unnecessary to provide for both kinds in the same form of joint. Accordingly, two forms of construction have been produced, to be used simultaneously in the same pipe system, one to provide for a longitudinal and the other for a rotary play of the pipes, the first to be confined to straight pipe lengths and the other to bends and fittings.
We have thus a dual pipe jointing system, Figs. 536 to 539, illustrating the construction for straight pipes, and Figs. 540 to 547 for bends and fittings.
Fig. 548 shows the means by which these joints are made up.
We have quite recently succeeded in obtaining a composition which has about the consistency of fresh putty when in the condition used by glaziers, with three very important other qualities, the first being a permanent plasticity due to the combination in the substance of a special form of non-drying oil, the second being practical indifference to all changes of temperature between the degrees of freezing and boiling water, and the third an extraordinary adhesiveness.
Our first work consisted in perfecting this composition after long experimenting with a very large number of substances, and testing it under all sorts of conditions for many years, until we were convinced of its practical reliability in all of these essential qualities required. After many years' exposure to dry air the compound has suffered no appreciable diminution of plasticity, and it appears capable of retaining all its desirable qualities in the joint indefinitely.
Describing first the plain pipe joint for longitudinal play, Figs. 536 and 537 show longitudinal sections of the device, and Fig. 538 is a horizontal section of the same. Fig. 539 shows the supporting and adjusting mechanism. As may be seen, the joint consists of the plain or spigot end of one pipe inserted into a spherical shaped enlargement of the opposite end of another pipe, the space between the two being filled with the permanently pliable compound already referred to. The spherical enlargement has between it and the main body of the pipe to which it is connected a short cylindrical enlargement of internal diameter just sufficient to receive the plain or spigot end of the other pipe, and of length sufficient to allow the latter to play back and forth longitudinally within the cylinder under the influence of expansion and contraction of the pipe line. The outer end of the spherical enlargement has a diameter just sufficient to receive the plain or spigot end of the other pipe. The pliable composition is forced into the space between the cup and spigot through a threaded hole in the side of the former, and is prevented from escaping by two soft, pliable gaskets at each end of the cup surrounding the spigot. In virtue of this arrangement the greater the internal pressure of fluids passing through the pipe system the more forcibly the elastic composition is forced against the gaskets and the more impervious they become. Accordingly, the greater the pressure the tighter becomes the joint. On the other hand, the great toughness and tenacity of the filling compound, and its permanent indifference to changes of temperature, present an absolutely impassable barrier to liquids or gases conveyed through the pipes under slight or atmospheric pressure, or even under more or less of a vacuum. The gaskets may be permeated with a material impervious to gases of any kind, and the filling composition is itself of a nature peculiarly adapted to withstand corroding chemical action.
The passage of boiling water, alternating with cold, through the pipes has no injurious effect on the materials forming the joint, nor does ice cold water nor a freezing outer environment produce any material reduction in the pliability and tenacity thereof.
The pliable compound is forced very quickly and easily into the joint under the pressure of the pumps shown in Fig. 548, and the pressure is afterwards maintained or even increased, if desired, by screwing down the small cap provided to close the opening after the pumping apparatus has been disconnected, but the principle of the construction of the joint does not seem to require the application of any special degree of pressure in inserting the filling material.
After the joint has been set up the filling may be applied and capped up in less than ten seconds on a four-inch pipe, and the jointing may be made as illustrated in this figure in situations absolutely inaccessible for ordinary methods of jointing, and its cost is far below that of any other joint of which the writer is aware.
A turned joint assembled by means of bolts has recently been placed on the market for street mains with a claim to some small degree of flexibility. But the expense of turning and bolting remains, and it is difficult to see how such a joint can be made either practically flexible or permanently tight under distorting influences.
A very important feature of advantage in the Securitas joint is the ease with which it may be disconnected at any time, as in case of desired alterations or extensions, and another very important advantage consists in its doing away with all use of heat in its construction. Cylinders containing the pliable compound for a large number of joints may be conveniently forwarded by mail or otherwise at a minimum of expense, the cylinders being constructed to fit the pumps in which they are used, and returnable for refilling at any time, and the pumps may be operated either by hand or by hydraulic air or steam pressure, or even by the weight of the workman, leaving his hands free for other work.