SURFACES AND CAPACITIES OF PIPES.

Pipe manufactured from double thick iron is called X-strong pipe, and pipe made double the thickness of X-strong is known as XX-strong pipe. Both X-strong and XX-strong pipe are furnished plain ends—no threads, unless specially ordered.

The table “Data relating to iron pipe” will be found especially useful to the engineer and steam fitter. The size of pipes referred to in the table range from ¹⁄₈ to 10 inches in diameter. In the successive columns are given the figures for the following important information:

1. Inside diameter of each size.
2. Outside diameter of each size.
3. External circumference of each size.
4. Length of pipe per square foot of outside surface.
5. Internal area of each size.
6. External area of each size.
7. Length of pipe containing one cubic foot.
8. Weight per foot of length of pipes.
9. Number of threads per inch of screw.
10. Contents in gallons (U. S. measure) per foot.
11. Weight of water per foot of length.

DATA

Relating to Iron Pipe.

The division of process in the manufacture of pipe, takes place at 1¹⁄₄ inch, 1¹⁄₄ inch and smaller sizes being called butt-welded pipe, and 1¹⁄₂ inch and larger sizes being known as lap-welded pipe; this rule holds good for standard, X-strong and XX-strong.

JOINTS OF PIPES AND FITTINGS.

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

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.

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.

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.

STEAM AND HOT WATER HEATING.

The heating by means of pipes through which are conveyed hot water and steam is a science by itself and yet one claiming some degree of familiarity by all engineers, steam users, and architects.

In practice it requires a knowledge of steam, air and temperatures, of pressure and supply; a familiarity with heat and heating surfaces and with all contrivances, appliances and devices that enter into the warming and ventilation of buildings. So long as factories, public and private buildings are erected, so long will warming and ventilation keep progress with steam engineering and remain a part of the general mechanical science required of the supervisory and practical engineer.

In what is called the system of open circulation, a supply main conveys the steam to the radiating surfaces, whence a return main conducts the condensed water either into an open tank for feeding the boiler, or into a drain to run to waste, the boiler being fed from some other source; the system of what is called closed circulation is carried out either with separate supply and return mains, both of which extend to the furthest distance to which the heat has to be distributed, or else with a single main, which answers at once for both the supply and the return, either with or without a longitudinal partition inside it for separating the outward current of steam supply from the return current of condensed water.

In either case suitable traps have to be provided on the return main, for preserving the steam pressure within the supply main and radiators. These two systems, in any of their modifications, may also be combined, as is most generally done in any extensive warming apparatus.

The system of closed circulation requires the boiler to be placed so low as will allow all the return pipes to drain freely back to it above its water-level. This condition has been modified mechanically by the automatic “trap,” a device frequently employed for lifting from a lower level, part or all of the condensed water, and delivering it into the boiler; it is, in fact, a displacement pump.

The same result has been attained by draining into a closed tank, placed low enough to accommodate all the return pipes, and made strong enough to stand the full boiler pressure with safety, and then employing a steam pump, either reciprocating or centrifugal, to raise the water from this tank to the proper level for enabling it to flow back into the boiler, the whole of the circulation being closed from communication with the atmosphere.

There are two systems of steam heating, known as the direct and the indirect system.

Direct radiating surfaces embrace all heaters placed within a room or building to warm the air, and are not directly connected with a system of ventilation.

Indirect radiation embraces all heating surfaces placed outside the rooms to be heated, and can only be used in connection with some system of ventilation.

For warming by direct radiation, the radiators usually consist of coils, composed of ³⁄₄-inch and 1-inch steam pipes, which are arranged in parallel lines and are coupled to branch tees or heads. In a few exceptional cases, radiators of peculiar shapes are specially constructed. In all cases the coils must have either vertical or horizontal elbows of moderate length, for allowing each pipe to expand separately and freely. Sometimes short lengths of pipe are coupled by return-bends, doubling backwards and forwards in several replications one above another, and forming what are called “return-bend coils,” and when several of these sections are connected by branch, tees into a compact mass of tubing, the whole is known as a “box-coil.”

Steam and Hot Water heating have long been acknowledged as altogether most practical and economical in every way—and their universal adoption in all the better class of buildings throughout the country is positive proof of their superiority.

The heat from steam is almost exactly identical with that from hot water, and few can distinguish between the two systems when properly erected.

They are both healthful, economical and satisfactory methods of warming. They give no gas, dust nor smoke; are automatically regulated, and therefore allow of an even and constant temperature throughout the house, whatever be the condition of the weather outside.

The circulation of the steam through the warming pipes is effected in an almost unlimited variety of ways, and the cause producing the circulation throughout the pipes of the warming apparatus is solely the difference of pressure which results from the more or less rapid condensation of the steam in contact with the radiating surfaces.

A partial vacuum is formed by this difference of pressure within the radiating portions of the apparatus, and the column of steam or of water equivalent to this diminution of pressure, constitutes the effective head producing the flow of steam from the boiler, at the same time the return current of condensed water is determined by the downward inclination of the pipes for the return course.

Points Relating to Steam Heating.

No two pipes should discharge into a T from opposite directions, thus retarding the motion of both or one of the returning currents. This is called “butting” and is one of the most vexatious things to encounter in pipe fitting.

All steam piped rooms should be frequently dusted, cleaned and kept free from accumulation of inflammable material.

The use of the air valve is as follows: In generating steam from cold water all the free air is liberated and driven off into the pipe, with the air left in them, all of which is forced up to the highest point of the coils or radiators, and compressed equal to the steam pressure following it. Now, by placing a valve or vent at the return end of the pieces to be heated, the air will be driven out by the compression. Why the vent is placed at the return is, that the momentum of the steam, it being the lightest body, will pass in the direction of it, falling down into the return as it condenses, thus liberating the air. Otherwise, should the vent not work, and the air is left in the radiator, it will act as an air spring, and the contents of the pipes left stationary will be the result; no circulation, no heat; and the greater steam pressure put on, the greater the chances are of not getting any heat; and thus a little device, with an opening no larger than a fine needle, will start what a ton of pressure would not do in its absence.

If the drip and supply pipes are large there is very little danger of freezing, provided suitable precautions are taken to leave the pipes clear. They should be blown through, when left, and the steam valve should be closed. There should also be a free chance for air to escape in all systems of piping.

No rule can be given relating to capacity for heating pipes and radiators which do not require to be largely modified by surroundings.

The field of steam heating would seem to be limitless—in one public building it required recently 480,000 dollars to meet the expenditures in this single line. As an example of warming on an extensive scale may be taken a large office in New York, of which the following are the particulars:

A second example is furnished by the State Lunatic Asylum at Indianapolis:

The “overhead” system of heating with steam pipes has several advantages. 1. The pipes are entirely out of the way 2. They do not become covered with odds and ends of unused materials. 3. If they leak the drip fixes the exact location of place needed to be repaired. 4. The room occupied overhead cannot be well otherwise utilized, hence in shops the system has proved efficient.

But for offices or store rooms the overhead system is not approved of owing to the heat beating down upon the occupants and causing headache.

When overhead heating pipes are used, they should not be hung too near the ceiling. If the room be a high one, it is better to hang them below, rather than above, the level of the belts running across the room, and they should not be less than three or four feet from the wall.

It is important to protect all wood work or other inflammable material around steam pipes from immediate contact with them, especially where pipes pass through floors and partitions. A metal thimble should be placed around the steam pipe, and firmly fastened on both sides of the floor, in such a way as to leave an air space around the steam pipe.

For indirect radiating surfaces, the box coils are the forms most used. The chambers or casings for containing them are made either of brickwork, or often of galvanized sheet-iron of No. 26 gauge, with folded joints. The coils are suspended freely within the chambers, which are themselves attached to the walls containing the air inlet flues. Besides coils of wrought iron tubes, cast-iron tablets or hollow slabs, having vertical surfaces with projecting studs or ribs, have been extensively used for the radiating surfaces.

As the amount of heat given off from the radiator cannot be satisfactorily controlled by throttling the steam supply, it is usual to divide all radiators into sections, each of which can be shut off from the supply and return mains, separately from the rest of the sections. This method of regulation applies to radiators for indirect heating as well as for direct.

Vertical pipe coils, constitute a distinctive form of radiator now largely used. In these a number of short upright 1-inch tubes, from two feet 8 inches to 2 feet 10 inches long, are screwed into a hollow cast iron base or box; and are either connected together in pairs by return-bends at their upper ends, or else each tube stands singly with its upper end closed, and having a hoop iron partition extending up inside it from the bottom to nearly the top. The supply of steam is admitted into the bottom casting; and the steam on entering, being lighter than the air, ascends through one leg of each siphon pipe and descends through the other, while the condensed water trickles down either leg, and with it the displaced air sinks also into the bottom box. For getting rid of the air, a trap is provided, having an outlet controlled by metallic rods; as soon as all the air has escaped and the rods become heated by the presence of unmixed steam, their expansion closes the outlet.

A thorough drainage of steam pipes will effectually prevent cracking and pounding noises.

The windward side of buildings require more radiating surface than does the sheltered side.

When floor radiators are used, their location should be determined by circumstances; the best situations are usually near the walls of the room, in front of the windows. The cold air, which always creates an indraft around the window frames, is thus, to some extent, warmed as it passes over the the radiators, and also assists in the general circulation.

Water of condensation will freeze quicker than water that has not been evaporated, for the reason that it has parted with all its air and is therefore solid.

Whatever the size of the circulating pipes, the supply and drip pipes should be large, to insure good circulation; the drip pipes especially so. This is also the more necessary when the pipes are exposed, or when there is danger of freezing after the steam is shut off.

It is important to see that no blisters or ragged pipes go into the returns, and also to make sure that the ends are not “burred in” with a dull pipe cutter wheel so as to form a place of lodgment for loose matter in the pipe to stop against.

Experiments recently made on the strength of bent pipes have developed some things not commonly known, or at least not recognized, that is, the strain on the inside of the angles, due to the effort of the pipes to straighten themselves under pressure. The problem is one of considerable intricacy, resolvable, however, by computation, and is a good one for practice. In the experiment referred to, a copper pipe of 6³⁄₄ in. bore, ³⁄₁₆ in. thick, was used. The angle was 90 degrees, and the legs about 16 in. long from the center. At a pressure of 912 pounds to an inch, the deflection of the pipe was nearly ³⁄₈ in., showing an enormous strain on the inner side, in addition to the pressure.

Steam valves should be connected in such a manner that the valve closes against the constant steam pressure.

Interesting experiments show that the loss by condensation in carrying steam one mile is 5 per cent. of the capacity of the main, and a steam pressure of seventy-five pounds carried in five miles of mains, ending at a point one-half mile from the boiler house only shows a loss of pressure of two pounds.

In steam warming it is necessary to bring the water to a boiling point to get any heat whatever; in hot water warming, a low temperature will radiate a corresponding amount of heat.

Never use a valve in putting in a low pressure apparatus if it is possible to get along without it. All the valves or cocks that are actually required in a well-proportioned low pressure apparatus are, a cock to blow off the water and clean out the return pipes, another to turn on the feed water. Of course the safety valves, gauge cocks, and those to shut fire regulators and such as are a part of the boiler, are not included in this “point.”

The most important thing in connecting the relief to return pipes is, that it should always be carried down below the line, the same as all vertical return pipes. In connecting the reliefs, so that the lower opening can at any time be exposed to the steam, there will be the difficulty of having the steam going in one direction, and the water in another.

The relief pipe should “tap” the steam at its lowest or most depressed points. It should always be put in at the base of all steam “risers” taking steam to upper floors.

In leaving the boiler with main steam pipe, raise to a height that will allow of one inch fall from the boiler to every ten feet of running steam pipe; this is sufficient, and a greater fall or pitch will cause the condensed water in the pipe to make at times a disagreeable noise or “gurgling.”

The flow pipe should never start from the boiler in a horizontal direction, as this will cause delay and trouble in the circulation. This pipe should always start in a vertical direction, even if it has to proceed horizontally within a short distance from the boiler. Reflection will show that the perfect apparatus is one that carries the flow pipe in a direct vertical line to the cylinder or tank; this is never, or but rarely possible, but skill and ingenuity should be exercised to carry the pipes as nearly as possible in this direction.

The flow of steam ought not to be fast enough to prevent the water of condensation from returning freely. All the circulating pipes should be lowest at the discharge end, and the inclination given them should not be less than one foot in fifty.