N. Hawkins

Figs. 641, 642.—See page 363.

PIPES AND FITTINGS.

A pipe was originally a wind instrument of music, consisting of a tube or tubes of straw, reed, wood or metal; in the literature of hydraulics this wind instrument becomes “a long tube or hollow body of wood, metal, earthenware, or the like; especially, one used as a conductor of water, steam, gas, etc.”

A pipe fitter is one who fits pipes together, or applies pipes, as to an engine or pump. A pipe fitter uses all the tools already described and in addition several others, as stretched lines, the spirit level and plumb-bob; he also uses special devices to aid in special cases; these are sometimes invented by himself and sometimes belong to “the trade-lore” transmitted in the long and varied operations of every successful shop. A pipe fitting is a piece, as a coupling, a valve, etc., used for connecting lengths of pipe or as accessory to a pipe. Joint comes from the word join and means the place or part where two things or parts are joined or united as a joint in a pipe. See note below.

Narrow surfaces make better and safer joints than wide ones; they are more quickly repaired with file or scraper, and they are less liable to catch dirt at the moment of making a joint. The limit of narrowness is that required to resist strains that might crush the metal and spoil the face of the joint.

Unless the joint is made metal to metal, fitting without any orifice, the jointing material is always softer than the pipes or other things to be joined. In this way the jointing need not have dead-true surfaces, but, yielding under pressure, it adapts itself to the space it has to fill. It must be dense enough and hard enough to resist all the working strains and influences that are likely to act upon it. The jointing of a steam pipe must resist the temperature of the steam, the water it carries with it, the changes of temperature when the pipe cools during intervals of work, and the strains due to the weight of the pipe, and also the internal pressure of the steam. If it expands differently from the metal in the pipe, it must be sufficiently elastic to compensate for this expansion, otherwise it will leak each time the pipes cool down.

The joint should be always inside the line of bolts, and if any joint material extends beyond, it would only help to support the flange in case it should spring. This, of course, indicates faulty design, for flanges ought to bear the strains of jointing without perceptible spring. Male and female flanges are best for high pressures.

A very popular joint is made with a planed or turned surface and a sheet of paper of the quality used to wrap bales of paper. This is the last survival of the millboard. Rubbed over the flange with a dirty hand and cut out with a penknife on a board, this is one of the cheapest jointings known. This paper has no lumps or grit in it, and if smeared with mineral cylinder oil it may be separated several times before it is spoiled. It is largely used on the faced joints of small engines and steam pumps. The mineral oil increases the life of the paper when exposed to high steam. Sheet asbestos is better.

Hydraulic joints for high pressure require greater rigidity than those of steam, but they do not have to bear high temperatures. The jointing material may be more or less plastic, such as leather, rubber or gutta percha. It is generally inclosed in a groove in the flange, and compressed by a projection fitting the groove, so that expansion of the jointing is arrested and the space is completely filled. There is no better principle for joints than this where packing is used between flanges. At a pressure of three tons to the inch, every square sixteenth of an inch must resist a power equal to twenty-six pounds; the joint must therefore be non-porous.

There are compounds used for making joints on which the plastic matter, which is subject to much change of volume between the liquid and solid state, is mixed with a neutral substance, like sand, which, combining mechanically with it, replaces from 90 to 95 per cent. of the total mass, and reduces its shrinkage to an inappreciable quantity.

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.

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.

Fig. 643 represents a male and female flange joint metal to metal combined with and forming a part of the pipe; it is used for special work and conditions. Fig. 644 is the usual screwed sleeve threaded connection with right hand coupling. Fig. 645 is a much used male and female flange union screwed for the reception of standard wrought iron pipe. Fig. 646 illustrates the common threaded malleable iron union and Fig. 647 the plain light malleable iron tee.

Steam Pipe Lines. These are constructed of cast iron or wrought iron and used for conveying a supply of steam from the boilers to engines, pumps, turbines and other machines driven by steam. Usually these lines are built up with straight pipe and “fittings.” The names of the latter are as follows: elbows; forty-fives (45°); tees; plugs; caps; reducers (or bushings); nipples; valves; unions (with ground, perishable, and flange joints); couplings (reducing and right and left); crosses; special fittings, such as elbows and tees of a nominal size reduced at some point to a smaller size to avoid the use of reducers; angle, check, and gate valves, and plug cocks; lock-nuts.

The proper anchoring and supporting of large steam mains is important. It is preferable to allow the system to expand in the proper direction without stress and at the same time avoiding vibration. The illustrations will give an idea of the method used in supporting pipes and allowing for expansion. Fig. 657 shows a wall bracket upon which the rollers supporting the pipe and allowing for the expansion and contraction are attached. Fig. 655 shows a bracket with an adjustable single roll, which may be adjusted to suit the pitch of the pipe at the same time allow the pipe to expand.

Fig. 655 shows a bracket with one adjustable roll designed for main steam pipes. This is an elaborate device but would be appreciated in buildings where everything is wanted to make up a strictly first class line of details.

Fig. 657 represents an extension of the same idea in which one bracket is made to carry two lines of pipe smaller than the one shown in the preceding illustration. Fig. 656 is a support made of one inch round iron and answers every purpose where all of these designs of pipe hangers permit of free expansion and contraction of the pipes.

It is bad practice to support the main steam pipes over boilers by hangers from the building as the building may settle in a different degree from the boiler hence the steam pipes are not properly supported, i.e., they are either strained unnecessarily by the strain upon the hangers or they are permitted to support themselves; it is better to support them by iron props underneath, made by screwing a flange upon the end of a piece of pipe of proper length and having a wrought iron crotch with thread and nut for adjustment inserted in the upper end.

The flange on the prop rests upon the boiler walls while the crotch fits the pipe and by means of the nut any desirable elevation of the steam pipe may be secured. For when the boilers settle as they will the pipes and connections all settle together.

Fig. 648 shows the common wrought iron right-hand sleeve coupling and Fig. 649 a plain lock nut.

Fig. 650 shows the bell and spigot connection commonly used for joining cast iron water or soil pipes, the joint being formed by pouring melted lead into the cavity inside the bell. The melted lead is prevented from escaping by damming up the opening with a turn of oakum at the bottom and fire clay at the top of the joint. After the lead cools it is calked with a calking tool. Fig. 651 is similar to Fig. 643 only the latter has plain flanges with a gasket, A, B, inserted.

Fig. 652 represents an improvement on the union shown in Fig. 646. It is known as the Dart-union. The improvement consists in the substitution of a ball and socket joint made of composition brass or bronze ground joint and enclosed within the malleable iron case; unions are particularly desirable for inaccessible locations where it would be next to impossible to reach the union to renew the gasket.

Fig. 653 is an extra heavy beaded malleable iron tee, while Fig. 654 shows a common threaded cast iron pipe plug.

The figures on page 366 are one half end views, divided on the center line, of brass and iron tubing; they are reduced in size, but show their relative thickness, from one eighth inch up to four inches inclusive.

The “Standard” sizes are shown in Figs. 663 and 664.

The “extra strong” are represented in Figs. 658, 661 and 662.

The double extra strong is shown in Figs. 659, 660, 665 and 666.

All “tubing,” including boiler tubes, is measured by the outside diameters, while gas and steam pipe, including cast iron water pipe is designated by the inside diameter.

Much might be said regarding duplicate pipe systems, both for and against. The general practice is coming to be that of subdividing into units, while in smaller plants the duplicate system is used. The service and conditions govern the method of piping, which should be such in every instance as to prevent a shut down due to accident in some part of the system.

All the fittings in the pipe system of a plant should be of the best quality, and the piping for high pressures should be extra heavy to withstand the test of time and usage. Water pipes, when of commercial wrought iron, should be galvanized.

In laying out a line of piping or in replacing a portion of an existing line the measurements should be taken from center to center of the various fittings; the allowance for the threaded part of the pipe can be made after the center-to-center and over-all measurements have been made and before the pipe is cut. Experience teaches what to allow for the threaded part on different sizes of pipe. The accompanying engraving gives an illustration of how the measurements on a pipe system are made.