Maxims and Instructions for the Boiler Room / Useful to Engineers, Firemen & Mechanics; Relating to Steam Generators, Pumps, Appliances, Steam Heating, Practical Plumbing, etc.

by N. Hawkins

JOINTS OF PIPES AND FITTINGS.

The accompanying illustrations represent certain joints, couplings and connections used in steam and hot water heating systems.

Fig. 115.

Fig. 116.

For many years in the matter of pipe joints there has been little change. The cast-iron hub and spigot joint, [Fig. 115], caulked with iron borings, is probably the oldest kind of joint. This is still generally adopted in hot water heating of a certain class, and was formerly used with low-pressure steam. A fairly regular smooth internal service is obtained, and once made tight is very durable. Cast-iron flanged pipes have also been a long time in use. These joints are made with a wrought-iron ring gasket, wrapped closely with yarn, [Fig. 116], which is sometimes dipped in a mixture of red and white lead. It is placed between the flanges, it being of such a diameter as to fit within the bolts by which the joint was screwed up and a nest or iron joint, B B, caulked outside the annular gasket between the faces of the flanges.

The next step in cast-iron flange pipe joints was the facing or turning up of the flanges and the use of a gasket of rubber, copper, paper or cement, with bolts for drawing the faces together. These joints for cast-iron pipes have not been changed excepting for some classes of work where a lip and recess, [Fig. 117], formed on opposite flanges, which makes the internal surfaces smooth and aid in preventing the gaskets from being blown out.

Fig. 117.

Fig. 118.

Fig. 119.

Fig. 120.

The introduction of wrought iron welded pipes has diminished the use of cast-iron pipes for many purposes, especially in heating apparatus and other pipe systems. Its advantages are lightness, the ease with which various lengths can be obtained and its strength. In wrought-iron pipe work the general practice in making joints between pipes is a wrought-iron coupling, [Fig. 118], with tapered threads at both ends. The pipes do not meet at their ends, and a recess of about ³⁄₄ inch or more long by the depth of the thickness of the pipes is left at every pipe end. A similar tapered thread is used in connecting the cast-iron fittings, elbows, tees, etc., [Fig. 119], to the pipe, and a large recess is necessary in each fitting to allow for the tapping of the threads. Thus the inside diameter of the fitting is larger by ¹⁄₈ inch than the outside diameter of the pipe, and the internal projection of the thickness of the pipe and that of the thread of the fitting increases materially the friction due to the interior surfaces of pipe and fitting. This class of joint requires care in the tapping of the fittings and in the cutting of tapered threads on the pipes; much trouble is caused by an inaccurately cut thread, as it may throw a line of pipes several inches out of place and put fittings and joints under undue and irregular strains.

Fig. 121.

Fig. 122.

The right and left threaded nipple, [Fig. 119], is used as a finishing connection joint and between fittings. Space equal to the length of the two threads is required between the two fittings to be connected in order to enter the nipple, and one or both fittings should be free to move in a straight line when the nipple is being screwed up. To make up this joint time and care are necessary. The right threaded end on nipple should be first firmly screwed with the tongs or wrench into the right threaded end of fitting, then slacked out and screwed up again by hand until tight, when it is screwed back by hand, at the same time counting the number of threads it has entered by hand. The same is done with the left threaded end of nipple and fitting. If the right and left threads of nipple have counted the same number of threads, each thread, when making the joint up, should enter the fittings at the same time if possible, and particular care must be taken that the fittings are exactly opposite, to facilitate catching on, prevent crossing threads, and that no irregular strain comes on the nipple while being screwed up.

In screwing up these nipples the coupling has to be turned with flats on the external surface to fit an internal wrench: in such cases the thread on nipple has one continuous taper. These special couplings are marked with ribs on the outside to distinguish them. [Fig. 120] represents another joint in wrought-iron piping known as the “union” composed of three pieces of the washer. Unions are also made with ground joints, and the washer dispensed with. Radiator valves are now generally connected by them, but if the hole in the radiator is not tapped accurately, the union when drawn up will not be tight, or if tight, the valve will not be straight.

[Fig. 121] shows right and left threaded nipple connecting elbow and tee with wrought-iron pipes.

The flange union, [Fig. 122], is another joint generally used on wrought-iron pipes above 4 or 5 inches in diameter in making connections to valves, etc., and on smaller pipes in positions where it is a convenient joint. This joint consists of two circular cast-iron flanges with the requisite number of holes for bolts, and central hole tapped tapered to receive thread of pipe. The abutting faces of the flanges are generally turned and the holding bolts fitted into the holes.