The New York Subway: Chapter 04, Power Plant from Coal Pile to Shafts of Engines and Turbines

From nycsubway.org

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.

Coal and Ash Hauling 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 convevors 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 buiikers 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 scrvice 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 svstem 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.

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 dowotakes 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.

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 lapjointed 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 .5 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.

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 7.5 x 13 x 6.5-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.

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.

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 i4-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 fr6m 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 2.5 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 socalled extra heavy proportions used in this country.

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.

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.

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, hut as a comparison of various dimensions and features of the Manhattan and Rapid Transit engines may be of interest, the accompanying tabulation is submitted:

Rapid Transit
Diameter of high-pressure cylinders, inches,4442
Diameter of low-pressure cylinders, inches,8886
Stroke, inches,6060
Speed, revolutions per minute,7575
Steam pressure at throttle, pounds,150175
Indicated horse power at best efficiency,7,5007,500
Diameter of low-pressure piston rods, inches,810
Diameter of high-pressure piston rods, inches,810
Diameter of crank pin, inches,1820
Length of crank pin, inches,1818
Diameter of shaft in journals, inches,3434
Length of journals, inches,6060
Diameter of shaft in hub of revolving element, inches,37 1/1637 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 he 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 successftilly with a steam pressure at the throttle of 175 pounds above atmos- phere, should the temperature of the steam he maintained at the throttle at from 450 to 500 degrees Fahr. Seventh. It will not require more than 12.25 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.

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, 937.5 kilowatts, 16.6 pounds per electrical horse power hour; one-half load, 625 kilowatts, 18.3 pounds and one quarter load, 312.5 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, 937.5 kilowatts, 14.6 pounds; one-half load, 625 kilowatts, 16.2 pounds; and one-quarter load, 312.5 kilowatts, 20.8 pounds.

Exciter Engines

The two exciter engines are each direct connected to a 250 kilowatt direct current generator. Each Engines 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 6oo indicated horse power.

Condensing Equipment

Each engine unit is supplied with its own condenser equipment, consisting of two barometic 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.

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 4o-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.

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.

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.

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.

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