As has been said, the tunnel between 157th Street and Fort George is the second longest two-track tunnel in the United States. It was built in a remarkably short time, considering the fact that the work was prosecuted from two portal headings and from two shafts. One shaft was at 168th Street and the other at 181st Street, the work proceeding both north and south from each shaft. The method employed for the work (Photograph on page 56) was similar to that used under Central Park. The shafts at 168th Street and at 181st Street were located at those points so that they might be used for the permanent elevator equipment for the stations at these streets. These stations each have an arch span of about 50 feet, lined with brick.

[Sidenote: Steel Viaduct]

The elevated viaduct construction extends from 125th Street to 133d Street and from Dyckman Street to Bailey Avenue on the western branch, and from Brook and Westchester Avenues to Bronx Park on the eastern, a total distance of about 5 miles. The three-track viaducts are carried on two column bents where the rail is not more than 29 feet above the ground level, and on four-column towers for higher structures. In the latter case, the posts of a tower are 29 feet apart transversely and 20 or 25 feet longitudinally, as a rule, and the towers are from 70 to 90 feet apart on centers. The tops of the towers have X-bracing and the connecting spans have two panels of intermediate vertical sway bracing between the three pairs of longitudinal girders. In the low viaducts, where there are no towers, every fourth panel has zigzag lateral bracing in the two panels between the pairs of longitudinal girders.



The towers have columns consisting as a rule of a 16 x 7/16-inch web plate and four 6 x 4 x 5/8-inch bulb angles. The horizontal struts in their cross-bracing are made of four 4 x 3-inch angles, latticed to form an I-shaped cross-section. The X-bracing consists of single 5 x 3-1/2-inch angles. The tops of the columns have horizontal cap angles on which are riveted the lower flanges of the transverse girders; the end angles of the girder and the top of the column are also connected by a riveted splice plate. The six longitudinal girders are web-riveted to the transverse girders. The outside longitudinal girder on each side of the viaduct has the same depth across the tower as in the connecting span, but the four intermediate lines are not so deep across the towers. In the single trestle bents the columns are the same as those just described, but the diagonal bracing is replaced by plate knee-braces.

The Manhattan Valley Viaduct on the West Side line, has a total length of 2,174 feet. Its most important feature is a two-hinged arch of 168-1/2 feet span, which carries platforms shaded by canopies, but no station buildings. The station is on the ground between the surface railway tracks. Access to the platforms is obtained by means of escalators. It has three lattice-girder two-hinge ribs 24-1/2 feet apart on centers, the center line of each rib being a parabola. Each half rib supports six spandrel posts carrying the roadway, the posts being seated directly over vertical web members of the rib. The chords of the ribs are 6 feet apart and of an H-section, having four 6 x 6-inch angles and six 15-inch flange and web plates for the center rib and lighter sections for the outside ribs. The arch was erected without false work.



The viaduct spans of either approach to the arch are 46 to 72 feet long. All transverse girders are 31 feet 4 inches long, and have a 70 x 3/8-inch web plate and four 6 x 4-inch angles. The two outside longitudinal girders of deck spans are 72 inches deep and the other 36 inches. All are 3/8-inch thick and their four flange angles vary in size from 5 x 3-1/2 to 6 x 6 inches, and on the longest spans there are flange plates. At each end of the viaduct there is a through span with 90-inch web longitudinal girders.

Each track was proportioned for a dead load of 330 pounds per lineal foot and a live load of 25,000 pounds per axle. The axle spacing in the truck was 5 feet and the pairs of axles were alternately 27 and 9 feet apart. The traction load was taken at 20 per cent. of the live load, and a wind pressure of 500 pounds per lineal foot was assumed over the whole structure.

[Sidenote: Tubes under Harlem River]

One of the most interesting sections of the work is that which approaches and passes under the Harlem River, carrying the two tracks of the East Side line. The War Department required a minimum depth of 20 feet in the river at low tide, which fixed the elevation of the roof of the submerged part of the tunnel. This part of the line, 641 feet long, consists of twin single-track cast-iron cylinders 16 feet in diameter enveloped in a large mass of concrete and lined with the same material. The approach on either side is a double-track concrete arched structure. The total length of the section is 1,500 feet.

The methods of construction employed were novel in subaqueous tunneling and are partly shown on photographs on pages 62 and 63. The bed of the Harlem River at the point of tunneling consists of mud, silt, and sand, much of which was so nearly in a fluid condition that it was removed by means of a jet. The maximum depth of excavation was about 50 feet. Instead of employing the usual method of a shield and compressed air at high pressure, a much speedier device was contrived.

The river crossing has been built in two sections. The west section was first built, the War Department having forbidden the closing of more than half the river at one time. A trench was dredged over the line of the tunnel about 50 feet wide and 39 feet below low water. This depth was about 10 feet above the sub-grade of the tunnel. Three rows of piles were next driven on each side of the trench from the west bank to the middle of the river and on them working platforms were built, forming two wharves 38 feet apart in the clear. Piles were then driven over the area to be covered by the subway, 6 feet 4 inches apart laterally and 8 feet longitudinally. They were cut off about 11 feet above the center line of each tube and capped with timbers 12 inches square. A thoroughly-trussed framework was then floated over the piles and sunk on them. The trusses were spaced so as to come between each transverse row of piles and were connected by eight longitudinal sticks or stringers, two at the top and two at the bottom on each side. The four at each side were just far enough apart to allow a special tongue and grooved 12-inch sheet piling to be driven between them. This sheathing was driven to a depth of 10 to 15 feet below the bottom of the finished tunnel.

A well-calked roof of three courses of 12-inch timbers, separated by 2-inch plank, was then floated over the piles and sunk. It had three timber shafts 7 x 17 feet in plan, and when it was in place and covered with earth it formed the top of a caisson with the sheet piling on the sides and ends, the latter being driven after the roof was in place. The excavation below this caisson was made under air pressure, part of the material being blown out by water jets and the remainder removed through the airlocks in the shafts. When the excavation was completed, the piles were temporarily braced and the concrete and cast-iron lining put in place, the piles being cut off as the concrete bed was laid up to them.

The second or eastern section of this crossing was carried on by a modification of the plan just mentioned. Instead of using a temporary timber roof on the side walls, the permanent iron and concrete upper half of the tunnels was employed as a roof for the caisson. The trench was dredged nearly to sub-grade and its sides provided with wharves as before, running out to the completed half of the work. The permanent foundation piles were then driven and a timber frame sunk over them to serve as a guide for the 12-inch sheet piling around the site. Steel pilot piles with water jets were driven in advance of the wood-sheet piles, and if they struck any boulders the latter were drilled and blasted. The steel piles were withdrawn by a six-part tackle and hoisting engine, and then the wooden piles driven in their place.

When the piling was finished, a pontoon 35 feet wide, 106 feet long, and 12 feet deep was built between the wharves, and upon a separate platform or deck on it the upper half of the cast-iron shells were assembled, their ends closed by steel-plate diaphragms and the whole covered with concrete. The pontoon was then submerged several feet, parted at its center, and each half drawn out endwise from beneath the floating top of the tunnel. The latter was then loaded and carefully sunk into place, the connection with the shore section being made by a diver, who entered the roof through a special opening. When it was finally in place, men entered through the shore section and cut away the wood bottom, thus completing the caisson so that work could proceed below it as before. Three of these caissons were required to complete the east end of the crossing.



The construction of the approaches to the tunnel was carried out between heavy sheet piling. The excavation was over 40 feet deep in places and very wet, and the success of the work was largely due to the care taken in driving the 12-inch sheet piling.

[Sidenote: Methods of Construction Brooklyn Extension]

A number of interesting features should be noted in the methods of construction adopted on the Brooklyn Extension.

The types of construction on the Brooklyn Extension have already been spoken of. They are (1) typical flat-roof steel beam subway from the Post-office, Manhattan, to Bowling Green; (2) reinforced concrete typical subway in Battery Park, Manhattan, and from Clinton Street to the terminus, in Brooklyn; (3) two single track cast-iron-lined tubular tunnels from Battery Park, under the East River, and under Joralemon Street to Clinton Street, Brooklyn.

Under Broadway, Manhattan, the work is through sand, the vehicular and electric street car traffic, the network of subsurface structures, and the high buildings making this one of the most difficult portions of the road to build. The street traffic is so great that it was decided that during the daytime the surface of the street should be maintained in a condition suitable for ordinary traffic. This was accomplished by making openings in the sidewalk near the curb, at two points, and erecting temporary working platforms over the street 16 feet from the surface. The excavations are made by the ordinary drift and tunnel method. The excavated material is hoisted from the openings to the platforms and passed through chutes to wagons. On the street surface, over and in advance of the excavations, temporary plank decks are placed and maintained during the drifting and tunneling operations, and after the permanent subway structure has been erected up to the time when the street surface is permanently restored. The roof of the subway is about 5 feet from the surface of the street, which has made it necessary to care for the gas and water mains. This has been done by carrying the mains on temporary trestle structures over the sidewalks. The mains will be restored to their former position when the subway structure is complete.

From Bowling Green, south along Broadway, State Street and in Battery Park, where the subway is of reinforced concrete construction, the "open cut and cover" method is employed, the elevated and surface railroad structures being temporarily supported by wooden and steel trusses and finally supported by permanent foundations resting on the subway roof. From Battery Place, south along the loop work, the greater portion of the excavation is made below mean high-water level, and necessitates the use of heavy tongue and grooved sheeting and the operation of two centrifugal pumps, day and night.

The tubes under the East River, including the approaches, are each 6,544 feet in length. The tunnel consists of two cast-iron tubes 15-1/2 feet diameter inside, the lining being constructed of cast-iron plates, circular in shape, bolted together and reinforced by grouting outside of the plates and beton filling on the inside to the depth of the flanges. The tubes are being constructed under air pressure through solid rock from the Manhattan side to the middle of the East River by the ordinary rock tunnel drift method, and on the Brooklyn side through sand and silt by the use of hydraulic shields. Four shields have been installed, weighing 51 tons each. They are driven by hydraulic pressure of about 2,000 tons. The two shields drifting to the center of the river from Garden Place are in water-bearing sand and are operated under air pressure. The river tubes are on a 3.1 per cent. grade and in the center of the river will reach the deepest point, about 94 feet below mean high-water level.

The typical subway of reinforced concrete from Clinton Street to the Flatbush Avenue terminus is being constructed by the method commonly used on the Manhattan-Bronx route. From Borough Hall to the terminus the route of the subway is directly below an elevated railway structure, which is temporarily supported by timber bracing, having its bearing on the street surface and the tunnel timbers. The permanent support will be masonry piers built upon the roof of the subway structure. Along this portion of the route are street surface electric roads, but they are operated by overhead trolley and the tracks are laid on ordinary ties. It has, therefore, been much less difficult to care for them during the construction of the subway. Work is being prosecuted on the Brooklyn Extension day and night, and in Brooklyn the excavation is made much more rapidly by employing the street surface trolley roads to remove the excavated material. Spur tracks have been built and flat cars are used, much of the removal being done at night.



CHAPTER III

POWER HOUSE BUILDING

The power house is situated adjacent to the North River on the block bounded by West 58th Street, West 59th Street, Eleventh Avenue, and Twelfth Avenue. The plans were adopted after a thorough study by the engineers of Interborough Rapid Transit Company of all the large power houses already completed and of the designs of the large power houses in process of construction in America and abroad. The building is large, and when fully equipped it will be capable of producing more power than any electrical plant ever built, and the study of the designs of other power houses throughout the world was pursued with the principal object of reducing to a minimum the possibility of interruption of service in a plant producing the great power required.

The type of power house adopted provides for a single row of large engines and electric generators, contained within an operating room placed beside a boiler house, with a capacity of producing, approximately, not less than 100,000 horse power when the machinery is being operated at normal rating.

[Sidenote: Location and General Plan of Power House]

The work of preparing the detailed plans of the power house structure was, in the main, completed early in 1902, and resulted in the present plan, which may briefly be described as follows: The structure is divided into two main parts—an operating room and a boiler house, with a partition wall between the two sections. The face of the structure on Eleventh Avenue is 200 feet wide, of which width the boiler house takes 83 feet and the operating section 117 feet. The operating room occupies the northerly side of the structure and the boiler house the southerly side. The designers were enabled to employ a contour of roof and wall section for the northerly side that was identical with the roof and wall contour of the southerly side, so that the building, when viewed from either end, presents a symmetrical appearance with both sides of the building alike in form and design. The operating room section is practically symmetrical in its structure, with respect to its center; it consists of a central area, with a truss roof over same along with galleries at both sides. The galleries along the northerly side are primarily for the electrical apparatus, while those along the southerly side are given up chiefly to the steam-pipe equipment. The boiler room section is also practically symmetrical with respect to its center.

A sectional scheme of the power house arrangement was determined on, by which the structure was to consist of five generating sections, each similar to the others in all its mechanical details; but, at a later date, a sixth section was added, with space on the lot for a seventh section. Each section embraces one chimney along with the following generating equipment:—twelve boilers, two engines, each direct connected to a 5,000 kilowatt alternator; two condensing equipments, two boiler-feed pumps, two smoke-flue systems, and detail apparatus necessary to make each section complete in itself. The only variation is the turbine plant hereafter referred to. In addition to the space occupied by the sections, an area was set aside, at the Eleventh Avenue end of the structure, for the passage of the railway spur from the New York Central tracks. The total length of the original five-section power house was 585 feet 9-1/2 inches, but the additional section afterwards added makes the over all length of the structure 693 feet 9-3/4 inches. In the fourth section it was decided to omit a regular engine with its 5,000 kilowatt generator, and in its place substitute a 5,000 kilowatt lighting and exciter outfit. Arrangements were made, however, so that this outfit can afterward be replaced by a regular 5,000 kilowatt traction generator.



The plan of the power station included a method of supporting the chimneys on steel columns, instead of erecting them through the building, which modification allowed for the disposal of boilers in spaces which would otherwise be occupied by the chimney bases. By this arrangement it was possible to place all the boilers on one floor level. The economizers were placed above the boilers, instead of behind them, which made a material saving in the width of the boiler room. This saving permitted the setting aside of the aforementioned gallery at the side of the operating room, closed off from both boiler and engine rooms, for the reception of the main-pipe systems and for a pumping equipment below it.

The advantages of the plan can be enumerated briefly as follows: The main engines, combined with their alternators, lie in a single row along the center line of the operating room with the steam or operating end of each engine facing the boiler house and the opposite end toward the electrical switching and controlling apparatus arranged along the outside wall. Within the area between the boiler house and operating room there is placed, for each engine, its respective complement of pumping apparatus, all controlled by and under the operating jurisdiction of the engineer for that engine. Each engineer has thus full control of the pumping machinery required for his unit. Symmetrically arranged with respect to the center line of each engine are the six boilers in the boiler room, and the piping from these six boilers forms a short connection between the nozzles on the boilers and the throttles on the engine. The arrangement of piping is alike for each engine, which results in a piping system of maximum simplicity that can be controlled, in the event of difficulty, with a degree of certainty not possible with a more complicated system. The main parts of the steam-pipe system can be controlled from outside this area.

The single tier of boilers makes it possible to secure a high and well ventilated boiler room with ventilation into a story constructed above it, aside from that afforded by the windows themselves. The boiler room will therefore be cool in warm weather and light, and all difficulties from escaping steam will be minimized. In this respect the boiler room will be superior to corresponding rooms in plants of older construction, where they are low, dark, and often very hot during the summer season. The placing of the economizers, with their auxiliary smoke flue connections, in the economizer room, all symmetrically arranged with respect to each chimney, removes from the boiler room an element of disturbance and makes it possible to pass directly from the boiler house to the operating room at convenient points along the length of the power house structure. The location of each chimney in the center of the boiler house between sets of six boilers divides the coal bunker construction into separate pockets by which trouble from spontaneous combustion can be localized, and, as described later, the divided coal bunkers can provide for the storage of different grades of coal. The unit basis on which the economizer and flue system is constructed will allow making repairs to any one section without shutting off the portions not connected directly to the section needing repair.

The floor of the power house between the column bases is a continuous mass of concrete nowhere less than two feet thick. The massive concrete foundations for the reciprocating engines contain each 1,400 yards of concrete above mean high water level, and in some cases have twice as much below that point. The total amount of concrete in the foundations of the finished power house is about 80,000 yards.



Water for condensing purposes is drawn from the river and discharged into it through two monolithic concrete tunnels parallel to the axis of the building. The intake conduit has an oval interior, 10 x 8-1/2 feet in size, and a rectangular exterior cross-section; the outflow tunnel has a horseshoe-shape cross-section and is built on top of the intake tunnel. These tunnels were built throughout in open trench, which, at the shore end, was excavated in solid rock. At the river end the excavation was, at some places, almost entirely through the fill and mud and was made in a cofferdam composed chiefly of sheet piles. As it was impossible to drive these piles across the old timber crib which formed the old dock front, the latter was cut through by a pneumatic caisson of wooden-stave construction, which formed part of one side of the cofferdam. At the river end of the cofferdam the rock was so deep that the concrete could not be carried down to its surface, and the tunnel section was built on a foundation of piles driven to the rock and cut off by a steam saw 19-1/2 feet below mean hightide. This section of the tunnel was built in a 65 x 48-foot floating caisson 24 feet deep. The concrete was rammed in it around the moulds and the sides were braced as it sunk. After the tunnel sections were completed, the caisson was sunk, by water ballast, to a bearing on the pile foundation.

Adjacent to the condensing water conduits is the 10 x 15-foot rectangular concrete tunnel, through which the underground coal conveyor is installed between the shore end of the pier and the power house.

[Sidenote: Steel Work]

The steel structure of the power house is independent of the walls, the latter being self-supporting and used as bearing walls only for a few of the beams in the first floor. Although structurally a single building, in arrangement it is essentially two, lying side by side and separated by a brick division wall.

There are 58 transverse and 9 longitudinal rows of main columns, the longitudinal spacing being 18 feet and 36 feet for different rows, with special bracing in the boiler house to accommodate the arrangement of boilers. The columns are mainly of box section, made up of rolled or built channels and cover plates. They are supported by cast-iron bases, resting on the granite capstones of the concrete foundation piers.

Both the boiler house and the engine house have five tiers of floor framing below the flat portion of the roof, the three upper tiers of the engine house forming galleries on each side of the operating room, which is clear for the full height of the building.

The boiler house floors are, in general, framed with transverse plate girders and longitudinal rolled beams, arranged to suit the particular requirements of the imposed loads of the boilers, economizers, coal, etc., while the engine-room floors and pipe and switchboard galleries are in general framed with longitudinal plate girders and transverse beams.

There are seven coal bunkers in the boiler house, of which five are 77 feet and two 41 feet in length by 60 feet in width at the top, the combined maximum capacity being 18,000 tons. The bunkers are separated from each other by the six chimneys spaced along the center line of the boiler house. The bottom of the bunkers are at the fifth floor, at an elevation of about 66 feet above the basement. The bunkers are constructed with double, transverse, plate girder frames at each line of columns, combined with struts and ties, which balance the outward thrust of the coal against the sides. The frames form the outline of the bunkers with slides sloping at 45 degrees, and carry longitudinal I-beams, between which are built concrete arches, reinforced with expanded metal, the whole surface being filled with concrete over the tops of the beams and given a two-inch granolithic finish.



The six chimneys, spaced 108 feet apart, and occupying the space between the ends of the adjacent coal bunkers, are supported on plate-girder platforms in the fifth floor, leaving the space below clear for a symmetrical arrangement of the boilers and economizers from end to end of the building. The platforms are framed of single-web girders 8 feet deep, thoroughly braced and carrying on their top flanges a grillage of 20-inch I-beam. A system of bracing for both the chimney platforms and coal bunkers is carried down to the foundations in traverse planes about 30 feet apart.

The sixth tier of beams constitute a flat roof over a portion of the building at the center and sides. In the engine room, at this level, which is 64 feet above the engine-room floor, are provided the two longitudinal lines of crane runway girders upon which are operated the engine-room cranes. Runways for 10-ton hand cranes are also provided for the full length of the boiler room, and for nearly the full length of the north panel in the engine room.

Some of the loads carried by the steel structure are as follows: In the engine house, operating on the longitudinal runways as mentioned, are one 60-ton and one 25-ton electric traveling crane of 75 feet span. The imposed loads of the steam-pipe galleries on the south side and the switchboard galleries on the north side are somewhat irregularly distributed, but are equivalent to uniform loads of 250 to 400 pounds per square foot. In the boiler house the weight of coal carried is about 45 tons per longitudinal foot of the building; the weight of the brick chimneys is 1,200 tons each; economizers, with brick setting, about 4-1/2 tons per longitudinal foot; suspended weight of the boilers 96 tons each, and the weight of the boiler setting, carried on the first floor framing, 160 tons each. The weight of structural steel used in the completed building is about 11,000 tons.

[Sidenote: Power House Superstructure]

The design of the facework of the power house received the personal attention of the directors of the company, and its character and the class of materials to be employed were carefully considered. The influence of the design on the future value of the property and the condition of the environment in general were studied, together with the factors relating to the future ownership of the plant by the city. Several plans were taken up looking to the construction of a power house of massive and simple design, but it was finally decided to adopt an ornate style of treatment by which the structure would be rendered architecturally attractive and in harmony with the recent tendencies of municipal and city improvements from an architectural standpoint. At the initial stage of the power house design Mr. Stanford White, of the firm of McKim, Mead & White, of New York, volunteered his services to the company as an adviser on the matter of the design of the facework, and, as his offer was accepted, his connection with the work has resulted in the development of the present exterior design and the selection of the materials used.

The Eleventh Avenue facade is the most elaborately treated, but the scheme of the main facade is carried along both the 58th and 59th Street fronts. The westerly end of the structure, facing the river, may ultimately be removed in case the power house is extended to the Twelfth Avenue building line for the reception of fourteen generating equipments; and for this reason this wall is designed plainly of less costly material.

The general style of the facework is what may be called French Renaissance, and the color scheme has, therefore, been made rather light in character. The base of the exterior walls has been finished with cut granite up to the water table, above which they have been laid up with a light colored buff pressed brick. This brick has been enriched by the use of similarly colored terra-cotta, which appears in the pilasters, about the windows, in the several entablatures, and in the cornice and parapet work. The Eleventh Avenue facade is further enriched by marble medallions, framed with terra-cotta, and by a title panel directly over the front of the structure.

The main entrance to the structure is situated at its northeast corner, and, as the railroad track passes along just inside the building, the entrance proper is the doorway immediately beyond the track, and opens into the entrance lobby. The doorway is trimmed with cut granite and the lobby is finished with a marble wainscoting.

The interior of the operating room is faced with a light, cream-colored pressed brick with an enameled brick wainscoting, eight feet high, extending around the entire operating area; the wainscoting is white except for a brown border and base. The offices, the toilets and locker rooms are finished and fitted with materials in harmony with the high-class character of the building. The masonry-floor construction consists of concrete reinforced with expanded metal, and except where iron or other floor plates are used, or where tile or special flooring is laid, the floor is covered with a hard cement granolithic finish.

In the design of the interior arrangements, the value of a generous supply of stairways was appreciated, in order that all parts of the structure might be made readily accessible, especially in the boiler house section. In the boiler house and machinery portion of the plant the stairways, railings, and accessories are plainly but strongly constructed. The main stairways are, however, of somewhat ornate design, with marble and other trim work, and the railings of the main gallery construction are likewise of ornate treatment. All exterior doors and trim are of metal and all interior carpenter work is done with Kalomein iron protection, so that the building, in its strictest sense, will contain no combustible material.

[Sidenote: Chimneys]

The complete 12-unit power house will have six chimneys, spaced 108 feet apart on the longitudinal center line of the boiler room, each chimney being 15 feet in inside diameter at the top, which is 225 feet above the grate bars. Each will serve the twelve boilers included in the section of which it is the center, these boilers having an aggregate of 72,000 square feet of heating surface. By these dimensions each chimney has a fair surplus capacity, and it is calculated that, with economizers in the path of the furnace gases, there will be sufficient draft to meet a demand slightly above the normal rating of the boilers. To provide for overload capacity, as may be demanded by future conditions, a forced draft system will be supplied, as described later.

As previously stated, the chimneys are all supported upon the steel structure of the building at an elevation of 76 feet above the basement floor and 63 feet above the grates. The supporting platforms are, in each case, carried on six of the building columns (the three front columns of two groups of boilers on opposite sides of the center aisle of the boiler room), and each platform is composed of single-web plate girders, well braced and surmounted by a grillage of 20-inch I-beams. The grillage is filled solidly with concrete and flushed smooth on top to receive the brickwork of the chimney.

Each chimney is 162 feet in total height of brickwork above the top of the supporting platform, and each chimney is 23 feet square in the outside dimension at the base, changing to an octagonal form at a point 14 feet 3 inches above the base. This octagonal form is carried to a height of 32 feet 6 inches above the base, at which point the circular section of radial brick begins.

The octagonal base of the chimney is of hard-burned red brick three feet in thickness between the side of the octagon and the interior circular section. The brick work is started from the top of the grillage platform with a steel channel curb, three feet in depth, through which two lines of steel rods are run in each direction, thus binding together the first three feet of brickwork, and designed to prevent any flaking at the outside. At a level of three feet above the bottom of the brickwork, a layer of water-proofing is placed over the interior area and covered with two courses of brick, upon which are built diagonal brick walls, 4 inches thick, 12 inches apart, and about 18 inches in height. These walls are themselves perforated at intervals, and the whole is covered with hand-burned terra-cotta blocks, thus forming a cellular air space, which communicates with the exterior air and serves as an insulation against heat for the steelwork beneath. A single layer of firebrick completes the flooring of the interior area, which is also flush with the bottom of the flue openings.

There are two flue openings, diametrically opposite, and 6 feet wide by 17 feet high to the crown of the arched top. They are lined with fire brick, which joins the fire-brick lining of the interior of the shaft, this latter being bonded to the red-brick walls to a point 6 feet below the top of the octagon, and extended above for a height of 14 feet within the circular shaft, as an inner shell. The usual baffle wall is provided of fire brick, 13 inches thick, extending diagonally across the chimney, and 4 feet above the tops of the flue openings.

Where the chimney passes through the roof of the boiler house, a steel plate and angle curb, which clears the chimney by 6 inches at all points, is provided in connection with the roof framing. This is covered by a hood flashed into the brickwork, so that the roof has no connection with or bearing upon the chimney.

At a point 4 feet 6 inches below the cap of the chimney the brickwork is corbeled out for several courses, forming a ledge, around the outside of which is placed a wrought-iron railing, thus forming a walkway around the circumference of the chimney top. The cap is of cast iron, surmounted by eight 3 x 1-inch wrought-iron ribs, bent over the outlet and with pointed ends gathered together at the center. The lightning conductors are carried down the outside of the shaft to the roof and thence to the ground outside of the building. Galvanized iron ladder rungs were built in the brickwork, for ladders both inside and outside the shaft.

The chimneys, except for the octagonal red-brick base, are constructed of the radial perforated bricks. The lightning rods are tipped with pointed platinum points about 18 inches long.

[Sidenote: North River Pier]

Exceptional facilities have been provided for the unloading of coal from vessels, or barges, which can be brought to the northerly side of the recently constructed pier at the foot of West 58th Street. The pier was specially built by the Department of Docks and Ferries and is 700 feet long and 60 feet wide.

The pier construction includes a special river wall across 58th Street at the bulkhead line through which the condensing water will be taken from and returned to the river. Immediately outside the river wall and beneath the deck of the pier, there is a system of screens through which the intake water is passed. On each side where the water enters the screen chamber, is a heavy steel grillage; inside this is a system of fine screens arranged so that the several screens can be raised, by a special machine, for the purpose of cleaning. The advantages of a well-designed screening outfit has been appreciated, and considerable care has been exercised to make it as reliable and effective as possible.

At each side of the center of the pier, just below the deck, there are two discharge water conduits constructed of heavy timber, to conduct the warm water from the condensers away from the cold water intakes at the screens. Two water conduits are employed, in order that one may be repaired or renewed while using the other; in fact, the entire pier is constructed with the view of renewal without interference in the operation for which it was provided.



CHAPTER IV

POWER PLANT FROM COAL PILE TO SHAFTS OF ENGINES AND TURBINES

From the minute and specific description in Chapter III, a clear idea will have been obtained of the power house building and its adjuncts, as well as of the features which not only go to make it an architectural landmark, but which adapt it specifically for the vital function that it is called upon to perform. We now come to a review and detailed description of the power plant equipment in its general relation to the building, and "follow the power through" from the coal pile to the shafts of the engines or steam turbines attached to the dynamos which generate current for power and for light.

[Sidenote: Coal and Ash Handling Equipment]

The elements of the coal handling equipment comprise a movable electric hoisting tower with crushing and weighing apparatus—a system of horizontal belt conveyors, with 30-inch belts, to carry the crushed and weighed coal along the dock and thence by tunnel underground to the southwest corner of the power house; a system of 30-inch belt conveyors to elevate the coal a distance of 110 feet to the top of the boiler house, at the rate of 250 tons per hour or more, if so desired, and a system of 20-inch belt conveyors to distribute it horizontally over the coal bunkers. These conveyors have automatic self reversing trippers, which distribute the coal evenly in the bunkers. For handling different grades of coal, distributing conveyors are arranged underneath the bunkers for delivering the coal from a particular bunker through gates to the downtake hoppers in front of the boilers, as hereafter described.

The equipment for removing ashes from the boiler room basement and for storing and delivering the ashes to barges, comprises the following elements: A system of tracks, 24 inches gauge, extending under the ash-hopper gates in the boiler-house cellar and extending to an elevated storage bunker at the water front. The rolling stock consists of 24 steel cars of 2 tons capacity, having gable bottoms and side dumping doors. Each car has two four-wheel pivoted trucks with springs. Motive power is supplied by an electric storage battery locomotive. The cars deliver the ashes to an elevating belt conveyor, which fills the ash bunker. This will contain 1,000 tons, and is built of steel with a suspension bottom lined with concrete. For delivering stored ashes to barges, a collecting belt extends longitudinally under the pocket, being fed by eight gates. It delivers ashes to a loading belt conveyor, the outboard end of which is hinged so as to vary the height of delivery and to fold up inside the wharf line when not in use.

The coal handling system in question was adopted because any serious interruption of service would be of short duration, as any belt, or part of the belt mechanism, could quickly be repaired or replaced. The system also possessed advantages with respect to the automatic even distribution of coal in the bunkers, by means of the self reversing trippers. These derive their power from the conveying belts. Each conveyor has a rotary cleaning brush to cleanse the belt before it reaches the driving pulley and they are all driven by induction motors.

The tower frame and boom are steel. The tower rolls on two rails along the dock and is self-propelling. The lift is unusually short; for the reason that the weighing apparatus is removed horizontally to one side in a separate house, instead of lying vertically below the crusher. This arrangement reduces by 40 per cent. the lift of the bucket, which is of the clam-shell type of forty-four cubic feet capacity. The motive power for operating the bucket is perhaps the most massive and powerful ever installed for such service. The main hoist is directly connected to a 200 horse-power motor with a special system of control. The trolley engine for hauling the bucket along the boom is also direct coupled to a multipolar motor.

The receiving hopper has a large throat, and a steel grizzly in it which sorts out coal small enough for the stokers and bypasses it around the crusher. The crusher is of the two-roll type, with relieving springs, and is operated by a motor, which is also used for propelling the tower. The coal is weighed in duplex two-ton hoppers.

Special attention has been given to providing for the comfort and safety of the operators. The cabs have baywindow fronts, to enable the men to have an unobstructed view of the bucket at all times without peering through slots in the floor. Walks and hand lines are provided on both sides of the boom for safe inspection. The running ropes pass through hardwood slides, which cover the slots in the engine house roof to exclude rain and snow.

This type of motive power was selected in preference to trolley locomotives for moving the ash cars, owing to the rapid destruction of overhead lines and rail bonds by the action of ashes and water. The locomotive consists of two units, each of which has four driving wheels, and carries its own motor and battery. The use of two units allows the locomotive to round curves with very small overhangs, as compared with a single-body locomotive. Curves of 12 feet radius can be turned with ease. The gross weight of the locomotive is about five tons, all of which is available for traction.

[Sidenote: Coal Downtakes]

The coal from the coal bunkers is allowed to flow down into the boiler room through two rows of downtakes, one on each side of the central gangway or firing place. Each bunker has eight cast-iron outlets, four on each side, and to these outlets are bolted gate valves for shutting off the coal from the corresponding downtakes. From these gates the downtakes lead to hoppers which are on the economizer floor, and from these hoppers the lower sets of downtakes extend down to the boilers.

Just above the hoppers on the economizer floor the coal downtakes are provided with valves and chutes to feed the coal, either into the hopper or into the distributing flight conveyor alongside of it. These distributing conveyors, one corresponding with each row of downtakes, permits the feeding of coal from any bunker or bunkers to all the boilers when desired. They are the ordinary type of flight conveyor, capable of running in either direction and provided with gates in the bottom of the trough for feeding into the several above mentioned hoppers. In order to eliminate the stresses that would develop in a conveyor of the full length of the building, the conveyors are of half the entire length, with electric driving engines in the center of each continuous line. The installation of this conveyor system, in connection with the coal downtakes, makes it possible to carry a high-grade coal in some of the bunkers for use during periods of heavy load and a cheaper grade in other bunkers for the periods of light load.

To provide means for shutting off the coal supply to each boiler, a small hopper is placed just over each boiler, and the downtake feeding into it is provided with a gate at its lower end. Two vertical downtakes extend down from the boiler hopper to the boiler room floor or to the stokers, as the case may be, and they are hinged just below the boiler hopper to allow their being drawn up out of the way when necessary to inspect the boiler tubes.



Wherever the direction of flow of the coal is changed, poke holes are provided in the downtakes to enable the firemen to break any arching tendency of the coal in the downtakes. All parts of the downtakes are of cast iron, except the vertical parts in front of the boilers, which are of wrought-iron pipe. These vertical downtakes are 10 inches in inside diameter, while all others are 14 inches in inside diameter.

[Sidenote: Main Boiler Room]

The main boiler room is designed to receive ultimately seventy-two safety water tube three drum boilers, each having 6,008 square feet of effective heating surface, by which the aggregate heating surface of the boiler room will be 432,576 square feet.

There are fifty-two boilers erected in pairs, or batteries, and between each battery is a passageway five feet wide. The boilers are designed for a working steam pressure of 225 pounds per square inch and for a hydraulic test pressure of 300 pounds per square inch. Each boiler is provided with twenty-one vertical water tube sections, and each section is fourteen tubes high. The tubes are of lap welded, charcoal iron, 4 inches in diameter and 18 feet long. The drums are 42 inches in diameter and 23 feet and 10 inches long. All parts are of open-hearth steel; the shell plates are 9/16 of an inch thick and the drum head plates 11/16 inch, and in this respect the thickness of material employed is slightly in excess of standard practice. Another advance on standard practice is in the riveting of the circular seams, these being lap-jointed and double riveted. All longitudinal seams are butt-strapped, inside and outside, and secured by six rows of rivets. Manholes are only provided for the front heads, and each front head is provided with a special heavy bronze pad, for making connection to the stop and check feed water valve.



The setting of the boiler embodies several special features which are new in boiler erection. The boilers are set higher up from the floor than in standard practice, the center of the drums being 19 feet above the floor line. This feature provides a higher combustion chamber, for either hand-fired grates or automatic stokers; and for inclined grate stokers the fire is carried well up above the supporting girders under the side walls, so that these girders will not be heated by proximity to the fire.

As regards the masonry setting, practically the entire inside surface exposed to the hot gases is lined with a high grade of fire brick. The back of the setting, where the rear cleaning is done, is provided with a sliding floor plate, which is used when the upper tubes are being cleaned. There is also a door at the floor line and another at a higher level for light and ventilation when cleaning. Over the tubes arrangements have been made for the reception of superheating apparatus without changing the brickwork. Where the brick walls are constructed, at each side of the building columns at the front, cast-iron plates are erected to a height of 8 feet on each side of the column. An air space is provided between each cast-iron plate and the column, which is accessible for cleaning from the boiler front; the object of the plates and air space being to prevent the transmission of heat to the steel columns.

An additional feature of the boiler setting consists in the employment of a soot hopper, back of each bridge wall, by which the soot can be discharged into ash cars in the basement. The main ash hoppers are constructed of 1/2-inch steel plate, the design being a double inverted pyramid with an ash gate at each inverted apex. The hoppers are well provided with stiffening angles and tees, and the capacity of each is about 80 cubic feet.

In front of all the boilers is a continuous platform of open-work cast-iron plates, laid on steel beams, the level of the platform being 8 feet above the main floor. The platform connects across the firing area, opposite the walk between the batteries, and at these points this platform is carried between the boiler settings. At the rear of the northerly row of boilers the platform runs along the partition wall, between the boiler house and operating room and at intervals doorways are provided which open into the pump area. The level of the platform is even with that of the main operating room floor, so that it may be freely used by the water tenders and by the operating engineers without being obstructed by the firemen or their tools. The platform in front of the boilers will also be used for cleaning purposes, and, in this respect, it will do away with the unsightly and objectionable scaffolds usually employed for this work. The water tenders will also be brought nearer to the water columns than when operating on the main floor. The feed-water valves will be regulated from the platform, as well as the speed of the boiler-feed pumps.

Following European practice, each boiler is provided with two water columns, one on each outside drum, and each boiler will have one steam gauge above the platform for the water tenders and one below the platform for the firemen. The stop and check valves on each boiler drum have been made specially heavy for the requirements of this power house, and this special increase of weight has been applied to all the several minor boiler fittings.

Hand-fired grates of the shaking pattern have been furnished for thirty-six boilers, and for each of these grates a special lower front has been constructed. These fronts are of sheet steel, and the coal passes down to the floor through two steel buckstays which have been enlarged for the purpose. There are three firing doors and the sill of each door is 36 inches above the floor. The gate area of the hand-fired grates is 100 square feet, being 8 feet deep by 12 feet 6 inches wide.

The twelve boilers, which will receive coal from the coal bunker located between the fourth and fifth chimneys, have been furnished with automatic stokers.

It is proposed to employ superheaters to the entire boiler plant.

The boiler-room ceiling has been made especially high, and in this respect the room differs from most power houses of similar construction. The distance from the floor to the ceiling is 35 feet, and from the floor plates over the boilers to the ceiling is 13 feet. Over each boiler is an opening to the economizer floor above, covered with an iron grating. The height of the room, as well as the feature of these openings, and the stairway wells and with the large extent of window opening in the south wall, will make the room light and especially well ventilated. Under these conditions the intense heat usually encountered over boilers will largely be obviated.

In addition to making provisions for the air to escape from the upper part of the boiler room, arrangements have been provided for allowing the air to enter at the bottom. This inflow of air will take place through the southerly row of basement windows, which extend above the boiler room floor, and through the wrought-iron open-work floor construction extending along in the rear of the northerly row of boilers.

A noteworthy feature of the boiler room is the 10-ton hand-power crane, which travels along in the central aisle through the entire length of the structure. This crane is used for erection and for heavy repair, and its use has greatly assisted the speedy assembling of the boiler plant.

[Sidenote: Blowers and Air Ducts]

In order to burn the finer grades of anthracite coal in sufficient quantities to obtain boiler rating with the hand-fired grates, and in order to secure a large excess over boiler rating with other coals, a system of blowers and air ducts has been provided in the basement under the boilers. One blower is selected for every three boilers, with arrangements for supplying all six boilers from one blower.

The blowers are 11 feet high above the floor and 5 feet 6 inches wide at the floor line. Each blower is direct-connected to a two crank 7-1/2 x 13 x 6-1/2-inch upright, automatic, compound, steam engine of the self-enclosed type, and is to provide a sufficient amount of air to burn 10,000 pounds of combustible per hour with 2 inches of water pressure in the ash pits.

[Sidenote: Smoke Flues and Economizers]

The smoke flue and economizer construction throughout the building is of uniform design, or, in other words, the smoke flue and economizer system for one chimney is identical with that for every other chimney. In each case, the system is symmetrically arranged about its respective chimney, as can be seen by reference to the plans.

The twelve boilers for each chimney are each provided with two round smoke uptakes, which carry the products of combustion upward to the main smoke flue system on the economizer floor. A main smoke flue is provided for each group of three boilers, and each pair of main smoke flues join together on the center line of the chimney, where in each case one common flue carries the gases into the side of the chimney. The two common flues last mentioned enter at opposite sides of the chimney. The main flues are arranged and fitted with dampers, so that the gases can pass directly to the chimney, or else they can be diverted through the economizers and thence reach the chimney.

The uptakes from each boiler are constructed of 3/8-inch plate and each is lined with radial hollow brick 4 inches thick. Each is provided with a damper which operates on a shaft turning in roller bearings. The uptakes rest on iron beams at the bottom, and at the top, where they join the main flue, means are provided to take up expansion and contraction.

The main flue, which rests on the economizer floor, is what might be called a steel box, constructed of 3/8-inch plate, 6 feet 4 inches wide and 13 feet high. The bottom is lined with brick laid flat and the sides with brick walls 8 inches thick, and the top is formed of brick arches sprung between.

[Sidenote: Steam Piping]

The sectional plan adopted for the power house has made a uniform and simple arrangement of steam piping possible, with the piping for each section, except that of the turbine bay, identical with that for every other section. Starting with the six boilers for one main engine, the steam piping may be described as follows: A cross-over pipe is erected on each boiler, by means of which and a combination of valves and fittings the steam may be passed through the superheater. In the delivery from each boiler there is a quick-closing 9-inch valve, which can be closed from the boiler room floor by hand or from a distant point individually or in groups of six. Risers with 9-inch wrought-iron goose necks connect each boiler to the steam main, where 9-inch angle valves are inserted in each boiler connection. These valves can be closed from the platform over the boilers, and are grouped three over one set of three boilers and three over the opposite set.

The main from the six boilers is carried directly across the boiler house in a straight line to a point in the pipe area where it rises to connect to the two 14-inch steam downtakes to the engine throttles. At this point the steam can also be led downward to a manifold to which the compensating tie lines are connected. These compensating lines are run lengthwise through the power house for the purpose of joining the systems together, as desired. The two downtakes to the engine throttles drop to the basement, where each, through a goose neck, delivers into a receiver and separating tank and from the tank through a second goose neck into the corresponding throttle.

A quick-closing valve appears at the point where the 17-inch pipe divides into the two 14-inch downtakes and a similar valve is provided at the point where the main connects to the manifold. The first valve will close the steam to the engine and the second will control the flow of steam to and from the manifold. These valves can be operated by hand from a platform located on the wall inside the engine room, or they can be closed from a distant point by hydraulic apparatus. In the event of accident the piping to any engine can be quickly cut out or that system of piping can quickly be disconnected from the compensating system.

The pipe area containing, as mentioned, the various valves described, together with the manifolds and compensating pipes, is divided by means of cross-walls into sections corresponding to each pair of main engines. Each section is thus separated from those adjoining, so that any escape of steam in one section can be localized and, by means of the quick-closing valves, the piping for the corresponding pair of main engines can be disconnected from the rest of the power house.



All cast iron used in the fittings is called air-furnace iron, which is a semi-steel and tougher than ordinary iron. All line and bent pipe is of wrought iron, and the flanges are loose and made of wrought steel. The shell of the pipe is bent over the face of the flange. All the joints in the main steam line, above 2-1/2 inches in size, are ground joints, metal to metal, no gaskets being used.

Unlike the flanges ordinarily used in this country, special extra strong proportions have been adopted, and it may be said that all flanges and bolts used are 50 per cent. heavier than the so-called extra heavy proportions used in this country.

[Sidenote: Water Piping]

The feed water will enter the building at three points, the largest water service being 12 inches in diameter, which enters the structure at its southeast corner. The water first passes through fish traps and thence through meters, and from them to the main reservoir tanks, arranged along the center of the boiler house basement. The water is allowed to flow into each tank by means of an automatic float valve. The water will be partly heated in these reservoir tanks by means of hot water discharged from high-pressure steam traps. In this way the heat contained in the drainage from the high-pressure steam is, for the most part, returned to the boilers. From the reservoir tanks the water is conducted to the feed-water pumps, by which it is discharged through feed-water heaters where it is further heated by the exhaust steam from the condensing and feed-water pumps. From the feed-water heaters the water will be carried direct to the boilers; or through the economizer system to be further heated by the waste gases from the boilers.



Like the steam-pipe system, the feed-water piping is laid out on the sectional plan, the piping for the several sections being identical, except for the connections from the street service to the reservoir tanks. The feed-water piping is constructed wholly of cast iron, except the piping above the floor line to the boilers, which is of extra heavy semi-annealed brass with extra heavy cast-iron fittings.

[Sidenote: Engine and Turbine Equipment]

The engine and turbine equipment under contract embraces nine 8,000 to 11,000 horse power main engines, direct-connected to 5,000 kilowatt generators, three steam turbines, direct-connected to 1,875 kilowatt lighting generators and two 400 horse power engines, direct-connected to 250 kilowatt exciter generators.

[Sidenote: Main Engines]

The main engines are similar in type to those installed in the 74th Street power house of the Manhattan Division of the Interborough Rapid Transit Company, i. e., each consists of two component compound engines, both connected to a common shaft, with the generator placed between the two component engines. The type of engine is now well known and will not be described in detail, but as a comparison of various dimensions and features of the Manhattan and Rapid Transit engines may be of interest, the accompanying tabulation is submitted:

Manhattan. Rapid Transit.

Diameter of high-pressure cylinders, inches, 44 42 Diameter of low-pressure cylinders, inches, 88 86 Stroke, inches, 60 60 Speed, revolutions per minute, 75 75 Steam pressure at throttle, pounds, 150 175 Indicated horse power at best efficiency, 7,500 7,500 Diameter of low-pressure piston rods, inches, 8 10 Diameter of high-pressure piston rods, inches, 8 10 Diameter of crank pin, inches, 18 20 Length of crank pin, inches, 18 18

Double Ported Single Ported Type of Low-Pressure Valves. Corliss Corliss Type of High-Pressure Valves. Corliss Poppet Type

Diameter of shaft in journals, inches, 34 34 Length of journals, inches, 60 60 Diameter of shaft in hub of revolving element, inches 37-1/16 37-1/16

The guarantees under which the main engines are being furnished, and which will govern their acceptance by the purchaser, are in substance as follows: First. The engine will be capable of operating continuously when indicating 11,000 horse power with 175 lbs. of steam pressure, a speed of 75 revolutions and a 26-inch vacuum without normal wear, jar, noise, or other objectionable results. Second. It will be suitably proportioned to withstand in a serviceable manner all sudden fluctuations of load as are usual and incidental to the generation of electrical energy for railway purposes. Third. It will be capable of operating with an atmospheric exhaust with two pounds back pressure at the low pressure cylinders, and when so operating, will fulfill all the operating requirements, except as to economy and capacity. Fourth. It will be proportioned so that when occasion shall require it can be operated with a steam pressure at the throttles of 200 pounds above atmospheric pressure under the before mentioned conditions of the speed and vacuum. Fifth. It will be proportioned so that it can be operated with steam pressure at the throttle of 200 pounds above atmospheric pressure under the before mentioned condition as to speed when exhausting in the atmosphere. Sixth. The engine will operate successfully with a steam pressure at the throttle of 175 pounds above atmosphere, should the temperature of the steam be maintained at the throttle at from 450 to 500 degrees Fahr. Seventh. It will not require more than 12-1/4 pounds of dry steam per indicated horse power per hour, when indicating 7,500 horse power at 75 revolutions per minute, when the vacuum of 26 inches at the low pressure cylinders, with a steam pressure at the throttle of 175 pounds and with saturated steam at the normal temperature due to its pressure. The guarantee includes all of the steam used by the engine or by the jackets or reheater.

The new features contained within the engine construction are principally: First, the novel construction of the high-pressure cylinders, by which only a small strain is transmitted through the valve chamber between the cylinder and the slide-surface casting. This is accomplished by employing heavy bolts, which bolt the shell of the cylinder casting to the slide-surface casting, said bolts being carried past and outside the valve chamber. Second, the use of poppet valves, which are operated in a very simple manner from a wrist plate on the side of the cylinder, the connections from the valves to the wrist plate and the connections from the wrist plate to the eccentric being similar to the parts usually employed for the operation of Corliss valves.

Unlike the Manhattan engines, the main steam pipes are carried to the high-pressure cylinders under the floor and not above it. Another modification consists in the use of an adjustable strap for the crank-pin boxes instead of the marine style of construction at the crank-pin end of the connecting rod.

The weight of the revolving field is about 335,000 pounds, which gives a flywheel effect of about 350,000 pounds at a radius of gyration of 11 feet, and with this flywheel inertia the engine is designed so that any point on the revolving element shall not, in operation, lag behind nor forge ahead of the position that it would have if the speed were absolutely uniform, by an amount greater than one-eighth of a natural degree.

[Sidenote: Turbo-Generators]

Arrangements have been made for the erection of four turbo generators, but only three have been ordered. They are of the multiple expansion parallel flow type, consisting of two turbines arranged tandem compound. When operating at full load each of the two turbines, comprising one unit, will develop approximately equal power for direct connection to an alternator giving 7,200 alternations per minute at 11,000 volts and at a speed of 1,200 revolutions per minute. Each unit will have a normal output of 1,700 electrical horse power with a steam pressure of 175 pounds at the throttle and a vacuum in the exhaust pipe of 27 inches, measured by a mercury column and referred to a barometric pressure of 30 inches. The turbine is guaranteed to operate satisfactorily with steam superheated to 450 degrees Fahrenheit. The economy guaranteed under the foregoing conditions as to initial and terminal pressure and speed is as follows: Full load of 1,250 kilowatts, 15.7 pounds of steam per electrical horse-power hour; three-quarter load, 937-1/2 kilowatts, 16.6 pounds per electrical horse-power hour; one-half load, 625 kilowatts, 18.3 pounds; and one-quarter load, 312-1/2 kilowatts, 23.2 pounds. When operating under the conditions of speed and steam pressure mentioned, but with a pressure in the exhaust pipe of 27 inches vacuum by mercury column (referred to 30 inches barometer), and with steam at the throttle superheated 75 degrees Fahrenheit above the temperature of saturated steam at that pressure, the guaranteed steam consumption is as follows: Full load, 1,250 kilowatts, 13.8 pounds per electrical horse-power hour; three-quarter load, 937-1/2 kilowatts, 14.6 pounds; one-half load, 625 kilowatts, 16.2 pounds; and one-quarter load, 312-1/2 kilowatts, 20.8 pounds.

[Sidenote: Exciter Engines]

The two exciter engines are each direct connected to a 250 kilowatt direct current generator. Each engine is a vertical quarter-crank compound engine with a 17-inch high pressure cylinder and a 27-inch low-pressure cylinder with a common 24-inch stroke. The engines will be non-condensing, for the reason that extreme reliability is desired at the expense of some economy. They will operate at best efficiency when indicating 400 horse power at a speed of 150 revolutions per minute with a steam pressure of 175 pounds at the throttle. Each engine will have a maximum of 600 indicated horse power.

[Sidenote: Condensing Equipment]

Each engine unit is supplied with its own condenser equipment, consisting of two barometric condensing chambers, each attached as closely as possible to its respective low-pressure cylinder. For each engine also is provided a vertical circulating pump along with a vacuum pump and, for the sake of flexibility, the pumps are cross connected with those of other engines and can be used interchangeably.

The circulating pumps are vertical, cross compound pumping engines with outside packed plungers. Their foundations are upon the basement floor level and the steam cylinders extend above the engine-room floor; the starting valves and control of speed is therefore entirely under the supervision of the engineer. Each pump has a normal capacity of 10,000,000 gallons of water per day, so that the total pumping capacity of all the pumps is 120,000,000 gallons per day. While the head against which these pumps will be required to work, when assisted by the vacuum in the condenser, is much less than the total lift from low tide water to the entrance into the condensing chambers, they are so designed as to be ready to deliver the full quantity the full height, if for any reason the assistance of the vacuum should be lost or not available at times of starting up. A temporary overload can but reduce the vacuum only for a short time and the fluctuations of the tide, or even a complete loss of vacuum cannot interfere with the constant supply of water, the governor simply admitting to the cylinders the proper amount of steam to do the work. The high-pressure steam cylinder is 10 inches in diameter and the low-pressure is 20 inches; the two double-acting water plungers are each 20 inches in diameter, and the stroke is 30 inches for all. The water ends are composition fitted for salt water and have valve decks and plungers entirely of that material.



The dry vacuum pumps are of the vertical form, and each is located alongside of the corresponding circulating pump. The steam cylinders also project above the engine-room floor. The vacuum cylinder is immediately below the steam cylinder and has a valve that is mechanically operated by an eccentric on the shaft. These pumps are of the close-clearance type, and, while controlled by a governor, can be changed in speed while running to any determined rate.

[Sidenote: Exhaust Piping]

From each atmospheric exhaust valve, which is direct-connected to the condensing chamber at each low-pressure cylinder, is run downward a 30-inch riveted-steel exhaust pipe. At a point just under the engine-room floor the exhaust pipe is carried horizontally around the engine foundations, the two from each pair of engines uniting in a 40-inch riser to the roof. This riser is between the pair of engines and back of the high-pressure cylinder, thus passing through the so-called pipe area, where it also receives exhaust steam from the pump auxiliaries. At the roof the 40-inch riser is run into a 48-inch stand pipe. This is capped with an exhaust head, the top of which is 35 feet above the roof.

All the exhaust piping 30 inches in diameter and over is longitudinally riveted steel with cast-iron flanges riveted on to it. Expansion joints are provided where necessary to relieve the piping from the strains due to expansion and contraction, and where the joints are located near the engine and generator they are of corrugated copper. The expansion joints in the 40-inch risers above the pipe area are ordinarily packed slip joints.

The exhaust piping from the auxiliaries is carried directly up into the pipe area, where it is connected with a feed-water heater, with means for by-passing the latter. Beyond the heater it joins the 40-inch riser to the roof. The feed-water heaters are three-pass, vertical, water-tube heaters, designed for a working water pressure of 225 pounds per square inch.

The design of the atmospheric relief valve received special consideration. A lever is provided to assist the valve to close, while a dash pot prevents a too quick action in either direction.

[Sidenote: Compressed Air]

The power house will be provided with a system for supplying compressed air to various points about the structure for cleaning electrical machinery and for such other purposes as may arise. It will also be used for operating whistles employed for signaling. The air is supplied to reservoir tanks by two vertical, two-stage, electric-driven air compressors.

[Sidenote: Oil System]

For the lubrication of the engines an extensive oil distributing and filtering system is provided. Filtered oil will be supplied under pressure from elevated storage tanks, with a piping system leading to all the various journals. The piping to the engines is constructed on a duplicate, or crib, system, by which the supply of oil cannot be interrupted by a break in any one pipe. The oil on leaving the engines is conducted to the filtering tanks. A pumping equipment then redelivers the oil to the elevated storage tanks.

All piping carrying filtered oil is of brass and fittings are inserted at proper pipes to facilitate cleaning. The immediate installation includes two oil filtering tanks at the easterly end of the power house, but the completed plant contemplates the addition of two extra filtering tanks at the westerly end of the structure.

[Sidenote: Cranes, Shops, Etc.]

The power house is provided with the following traveling cranes: For the operating room: One 60-ton electric traveling crane and one 25-ton electric traveling crane. For the area over the oil switches: one 10-ton hand-operated crane. For the center aisle of the boiler room: one 10-ton hand-operated crane. The span of both of the electric cranes is 74 feet 4 inches and both cranes operate over the entire length of the structure.

The 60-ton crane has two trolleys, each with a lifting capacity, for regular load, of 50 tons. Each trolley is also provided with an auxiliary hoist of 10 tons capacity. When loaded, the crane can operate at the following speeds: Bridge, 200 feet per minute; trolley, 100 feet per minute; main hoist, 10 feet per minute; and auxiliary hoist, 30 feet per minute. The 25-ton crane is provided with one trolley, having a lifting capacity, for regular load, of 25 tons, together with auxiliary hoist of 5 tons. When loaded, the crane can operate at the following speeds: bridge, 250 feet per minute; trolley, 100 feet per minute; main hoist, 12 feet per minute; and auxiliary hoist, 28 feet per minute.

The power house is provided with an extensive tool equipment for a repair and machine shop, which is located on the main gallery at the northerly side of the operating room.



CHAPTER V

SYSTEM OF ELECTRICAL SUPPLY

[Sidenote: Energy from Engine Shaft to Third Rail]

The system of electrical supply chosen for the subway comprises alternating current generation and distribution, and direct current operation of car motors. Four years ago, when the engineering plans were under consideration, the single-phase alternating current railway motor was not even in an embryonic state, and notwithstanding the marked progress recently made in its development, it can scarcely yet be considered to have reached a stage that would warrant any modifications in the plans adopted, even were such modifications easily possible at the present time. The comparatively limited headroom available in the subway prohibited the use of an overhead system of conductors, and this limitation, in conjunction with the obvious desirability of providing a system permitting interchangeable operation with the lines of the Manhattan Railway system practically excluded tri-phase traction systems and led directly to the adoption of the third-rail direct current system.



It being considered impracticable to predict with entire certainty the ultimate traffic conditions to be met, the generator plant has been designed to take care of all probable traffic demands expected to arise within a year or two of the beginning of operation of the system, while the plans permit convenient and symmetrical increase to meet the requirements of additional demand which may develop. Each express train will comprise five motor cars and three trail cars, and each local train will comprise three motor cars and two trail cars. The weight of each motor car with maximum live load is 88,000 pounds, and the weight of each trailer car 66,000 pounds.

The plans adopted provide electric equipment at the outstart capable of operating express trains at an average speed approximating twenty-five miles per hour, while the control system and motor units have been so chosen that higher speeds up to a limit of about thirty miles per hour can be attained by increasing the number of motor cars providing experience in operation demonstrates that such higher speeds can be obtained with safety.

The speed of local trains between City Hall and 96th Street will average about 15 miles an hour, while north of 96th Street on both the West side and East side branches their speed will average about 18 miles an hour, owing to the greater average distance between local stations.

As the result of careful consideration of various plans, the company's engineers recommended that all the power required for the operation of the system be generated in a single power house in the form of three-phase alternating current at 11,000 volts, this current to be generated at a frequency of 25 cycles per second, and to be delivered through three-conductor cables to transformers and converters in sub-stations suitably located with reference to the track system, the current there to be transformed and converted to direct current for delivery to the third-rail conductor at a potential of 625 volts.



Calculations based upon contemplated schedules require for traction purposes and for heating and lighting cars, a maximum delivery of about 45,000 kilowatts at the third rail. Allowing for losses in the distributing cables, in transformers and converters, this implies a total generating capacity of approximately 50,000 kilowatts, and having in view the possibility of future extensions of the system it was decided to design and construct the power house building for the ultimate reception of eleven 5,000-kilowatt units for traction current in addition to the lighting sets. Each 5,000-kilowatt unit is capable of delivering during rush hours an output of 7,500 kilowatts or approximately 10,000 electrical horse power and, setting aside one unit as a reserve, the contemplated ultimate maximum output of the power plant, therefore, is 75,000 kilowatts, or approximately 100,000 electrical horse power.

[Sidenote: Power House]

The power house is fully described elsewhere in this publication, but it is not inappropriate to refer briefly in this place to certain considerations governing the selection of the generating unit, and the use of engines rather than steam turbines.



The 5,000-kilowatt generating unit was chosen because it is practically as large a unit of the direct-connected type as can be constructed by the engine builders unless more than two bearings be used—an alternative deemed inadvisable by the engineers of the company. The adoption of a smaller unit would be less economical of floor space and would tend to produce extreme complication in so large an installation, and, in view of the rapid changes in load which in urban railway service of this character occur in the morning and again late in the afternoon, would be extremely difficult to operate.

The experience of the Manhattan plant has shown, as was anticipated in the installation of less output than this, the alternators must be put in service at intervals of twenty minutes to meet the load upon the station while it is rising to the maximum attained during rush hours.

After careful consideration of the possible use of steam turbines as prime-movers to drive the alternators, the company's engineers decided in favor of reciprocating engines. This decision was made three years ago and, while the steam turbine since that time has made material progress, those responsible for the decision are confirmed in their opinion that it was wise.



[Sidenote: Alternators]

The alternators closely resemble those installed by the Manhattan Railway Company (now the Manhattan division of the Interborough Rapid Transit Company) in its plant on the East River, between 74th Street and 75th Street. They differ, however, in having the stationary armature divided into seven castings instead of six, and in respect to details of the armature winding. They are three-phase machines, delivering twenty-five cycle alternating currents at an effective potential of 11,000 volts. They are 42 feet in height, the diameter of the revolving part is 32 feet, its weight, 332,000 pounds, and the aggregate weight of the machine, 889,000 pounds. The design of the engine dynamo unit eliminates the auxiliary fly wheel generally used in the construction of large direct-connected units prior to the erection of the Manhattan plant, the weight and dimensions of the revolving alternator field being such with reference to the turning moment of the engine as to secure close uniformity of rotation, while at the same time this construction results in narrowing the engine and reducing the engine shafts between bearings.



Construction of the revolving parts of the alternators is such as to secure very great strength and consequent ability to resist the tendency to burst and fly apart in case of temporary abnormal speed through accident of any kind. The hub of the revolving field is of cast steel, and the rim is carried not by the usual spokes but by two wedges of rolled steel. The construction of the revolving field is illustrated on pages 91 and 92. The angular velocity of the revolving field is remarkably uniform. This result is due primarily to the fact that the turning movement of the four-cylinder engine is far more uniform than is the case, for example, with an ordinary two-cylinder engine. The large fly-wheel capacity of the rotating element of the machine also contributes materially to secure uniformity of rotation.



The alternators have forty field poles and operates at seventy-five revolutions per minute. The field magnets constitute the periphery of the revolving field, the poles and rim of the field being built up by steel plates which are dovetailed to the driving spider. The heavy steel end plates are bolted together, the laminations breaking joints in the middle of the pole. The field coils are secured by copper wedges, which are subjected to shearing strains only. In the body of the poles, at intervals of approximately three inches, ventilating spaces are provided, these spaces registering with corresponding air ducts in the external armature. The field winding consists of copper strap on edge, one layer deep, with fibrous material cemented in place between turns, the edges of the strap being exposed.



The armature is stationary and exterior to the field. It consists of a laminated ring with slots on its inner surface and supported by a massive external cast-iron frame. The armature, as has been noted, comprises seven segments, the topmost segment being in the form of a small keystone. This may be removed readily, affording access to any field coil, which in this way may be easily removed and replaced. The armature winding consists of U-shaped copper bars in partially closed slots. There are four bars per slot and three slots per phase per pole. The bars in any slot may be removed from the armature without removing the frame. The alternators, of course, are separately excited, the potential of the exciting current used being 250 volts.

As regards regulation, the manufacturer's guarantee is that at 100 per cent. power factor if full rated load be thrown off the e. m. f. will rise 6 per cent. with constant speed and constant excitation. The guarantee as to efficiency is as follows: On non-inductive load, the alternators will have an efficiency of not less than 90.5 per cent. at one-quarter load; 94.75 per cent. at one-half load; 96.25 per cent. at three-quarters load; 97 per cent. at full load, and 97.25 per cent. at one and one-quarter load. These figures refer, of course, to electrical efficiency, and do not include windage and bearing friction. The machines are designed to operate under their rated full load with rise of temperature not exceeding 35 degrees C. after twenty-four hours.



[Sidenote: Exciters]

To supply exciting current for the fields of the alternators and to operate motors driving auxiliary apparatus, five 250-kilowatt direct current dynamos are provided. These deliver their current at a potential of 250 volts. Two of them are driven by 400 horse-power engines of the marine type, to which they are direct-connected, while the remaining three units are direct-connected to 365 horse-power tri-phase induction motors operating at 400 volts. A storage battery capable of furnishing 3,000 amperes for one hour is used in co-operation with the dynamos provided to excite the alternators. The five direct-current dynamos are connected to the organization of switching apparatus in such a way that each unit may be connected at will either to the exciting circuits or to the circuits through which auxiliary motors are supplied.