Fig. 653.
Another class of joints is that into which the jointing material is poured in a liquid state. Most of those liquids, such as lead, pitch, putty, sealing-wax, beeswax, or clay, shrink when they dry or cool. Others, like Portland cement and certain metallic alloys, do not change in volume. Others, again, like sulphur and plaster of Paris, increase in volume in setting. These substances all vary in their elasticity, qualities of density, hardness, and powers of resisting heat, cold and moisture. The duty of a joint must, therefore, be well considered before the material is chosen, after which the recess in which it is to lie must be carefully designed so as to firmly hold the material and with the least possible waste.
Fig. 654.
Kerosene, from its solvent powers, will destroy joints of rubber or of cements compounded with oils. Kerosene tanks are, therefore, rust-jointed and calked. As kerosene does not dissolve anything that is soluble in water or alcohol, kerosene casks are coated with glue to make them tight. India rubber may be used as a kerosene joint if inclosed like the hydraulic joint, and prevented from swelling. It is then unable to absorb the liquid. But leather is very much better.
In making up a piece of piping in which several fittings are quite close together, each fitting is tightened separately; do not follow the common practice of making up loosely at first and then tightening all together by applying a wrench to the fitting farthest from the main connection, as this process does not insure tight joints and the intermediate fittings, nipples, etc., are subjected to an unnecessary torsional strain.
The proper arrangement of pipe connections have already been alluded to in Part One, page 222; it is a subject whose importance can scarcely be magnified for if any difficulty is experienced in making a pump work properly when first started, it will generally be found to proceed from imperfect connections, and this remains true quite to the end of the usefulness of the pump. By a careful study of the illustration above mentioned, a good degree of attention will be repaid.
Figs. [641] and [642] represent pipes which are specially intended for mine pump columns or discharge pipes. They are made in sizes from six inches to thirty inches outside diameter; they are of wrought iron, lap welded and tested to a pressure of five hundred pounds to the square inch; they are fitted with cast iron or steel flanges, bolts and gaskets which face square with the center line of the pipe.
These flanges are shrunk on the pipe as shown in the figures, expanded and flared inside.