Rendering of the MLG&W Artesian Well Parkway Pumping Station now known as the Mallory Pumping Station, 488 North Dunlap St., Memphis TN - Circa 1922
How Memphis Water Works Is Planning For Future Needs
Recommended Program of Engineers—How It Is Being Carried Out— Detailed Description of Improvements—Cost Nearly Three Million
THE handling of large and important water works problems, especially when the future of a city hangs upon the proper formulation and carrying out of the program of development of its water supply, is always interesting. The following outline of the system being introduced in the water works of Memphis, Tenn., written by the engineer in charge of these developments, will be found particularly instructive. The experience of Mr. McClintock for the past seventeen years has been entirely identified with the work of George W. Fuller and the late Rudolph Hering. Mr. Fuller and Mr. McClintock have been in partnership since 1912 and from 1915 up to the present time the business has been under the firm name of Fuller & McClintock. For the past three years Mr. McClintock spent the greater portion of his time on the report of the Memphis water works project and that of Kansas City, Mo. Previous to that time he had charge of comprehensive sewer work and the sewage pumping station in the city of Toledo.
In March 1922, the writer’s firm submitted a report on the Water Supply of Memphis following a detailed investigation of the local water problem. The principal recommendations and conclusions of the report were as follows:
Recommended Program for New Supply Works
It is entirely practicable to develop a well water supply at Memphis of 75 million gallons daily or more, and there is no probability of a well designed and adequately developed artesian supply failing to meet all municipal and industrial needs during the next thirty years.
The artesian water is naturally excellent in quality, being clear, cool, soft and practically free from organic matter and bacteria. This ground water, however, contains considerable free carbonic acid, the amount ranging from 90 to 130 parts per million, which makes it highly corrosive of cast iron pipe.
The iron content of the Memphis wells varies from about 0.2 parts per million to a maximum of 6 parts per million and the high carbonic acid causes substantial amounts of iron to be dissolved as the water flows through the iron pipe system. When dissolved iron is present in quantities greater than about 0.4 parts per million it causes unsightly stains upon plumbing fixtures, kitchen utensils, and particularly white goods in the laundry. The removal of iron and carbonic acid is therefore an essential feature for a satisfactory future well supply.
It was recommended that the Auction Avenue development be abandoned as soon as new supply works could be put in service. Most of the present wells arc of such age and condition as to be of doubtful serviceability and are potentially subject to pollution. The fine sands in this vicinity preclude large yields of water being economically secured and there is grave doubt as to the continued integrity of the main tunnel and more particularly the timber lined drifts connecting with the wells. It was also deemed advisable to abandon the Central Avenue plant as soon as practicable, because it is uneconomical to operate and the site is not a good one for the further development of wells because of the distance from the ground surface to the artesian water plane.
The fourteen segregated wells are expensive to operate regularly and at times they discharge troublesome quantities of sand into the pipe system. On starting up these wells, after a shut down, objectionable amounts of rust are delivered into the mains. Some of them should prove serviceable for 8 or 10 years for emergency use during periods of high consumption, and their continued use as a reserve is perhaps advisable.
The Mississippi River has been frequently suggested as a source of water supply for Memphis and it is perfectly feasible to obtain a satisfactory filtered water supply from the river as is done at St. Louis and New Orleans. Such a supply would be much harder than the artesian water and also noticeably warmer in summer although free front iron and excessive free carbonic acid. It would be cheaper to treat the artesian supply by aeration and filtration to remove iron and carbonic acid than to remove the sediment and bacteria from the river water.
A satisfactory intake in the Mississippi River would be relatively difficult and expensive to obtain at Memphis owing to the absence of rock bottom and the shifting character of the river channel.
The investment for a river supply would be nearly twice that necessary for a complete, first class, modern, artesian water development of equal capacity and the total annual costs would be largely in excess of the corresponding annual costs for a well water supply. It was therefore recommended that the Mississippi River be dismissed from consideration as a source of supply.
The probable increase in population has been judged by the past growth of Memphis and compared with the earlier growth of similar cities. The assumed growth for Memphis is similar to that enjoyed by Cincinnati for several decades and a little higher than the growth of Louisville and New Orleans. It is not so rapid, however, as has occured in Indianapolis, Kansas City and St. Louis.
The water consumption estimates were based on the actual per capita consumption at Memphis, but for the future have been increased somewhat, as such a tendency to increase throughout a period of years is generally noted in most cities, notwithstanding all attempts to curtail waste.
The city may be arbitrarily divided into two areas designated the Eastern and Western Districts, respectively.
The plot of land in the northwest portion of the city, already owned by the water department, known as the Dunlap Street site is favorably situated for a new well water development. This site is adjacent to the North Parkway, which is an excellent location for wells, and it is also reasonably near to the more densely built up western portion of the city where the heaviest water consumption occurs. After careful study of other well projects it was determined that the most economical plan would be to develop works at Dunlap Street of sufficient capacity to provide for the full draft in the Western District for a period of 30 years or more. Such a plant would then have sufficient capacity to supply the entire city for a period of 8 or 10 years. Before the capacity of the Dunlap Street station is exceeded by the increasing consumption in the Western District, a new eastern station should be constructed at some location where the length of connecting lines to the distribution system will not be excessive, and a suitable area for sinking wells can be obtained, at which the depths from the surface to the artesian water plane is not too great for economical operation.
The new works should comprise a modern, steamoperated, high lift pumping station; a covered reservoir to equalize peak rates of water consumption and furnish a reserve for fire purposes; suitable aerating arrangements and filters for removing free carbonic acid and iron; and a new system of wells extending eastward along North Parkway for supplying this station through a suitable collecting conduit. Discharge mains should be installed to deliver the water into the present distribution system.
The free carbonic acid content is greatly reduced by the air lift method of pumping water from the wells, about 80 per cent. being removed. This was conclusively proven by experiment and by observation of air lift installations in various parts of the city. To insure against corrosion in street mains and consequent increase in iron content, the carbonic acid should be reduced to 10 parts or less, which result can best be obtained by suitable aeration through coke beds together with the application of small quantities of lime.
The iron can be readily and completely removed by passing the water through rapid sand filters at normal rates for mechanical filters and can be completely removed from fully aerated water by such means only.
The advantages of a highly polished, sparkling product from the city water works fully warrant the relatively small expense of removing the iron and carbonic acid. By carrying out these recommendations the citizens will obtain freedom from iron stains and the unusually high corrosive action of the artesian water. Memphis will then have a city water equaled by few sizeable cities in the world and surpassed by none.
The air lift is the best method for raising water from wells and delivering it to the treatment works at Dunlap Street. Electrically operated deep well pumps would be somewhat more expensive and do not showthe advantage which the air lift possesses in removing the larger part of the free carbonic acid.
As a result of the report the city decide to construct new water supply works in substantial accordance with the recommendations. Work on plans and specifications were commenced in April, 1922, and contracts for machinery let in July 1922. To date, practically all work is under contract and construction of the pumping station, pumping equipment, and other portions of the works is well advanced. It is expected that the new works will be completed and in operation early in 1924. The following is a general description of the work:
Parkway Station Layout
The water of the Parkway Station from the wells enters the equalizing basin which provides for variations between the flow from the wells and the rate of operation of the aerator and iron removal plant. From the equalizing basin the water flows to the secondary pumps in the north end of the pumping station which discharge through a 42-inch cast iron conduit to the aerator. A Venturi meter is provided in this conduit for measuring the flow of water to the aerator. After passing through the aerator the water goes through the filters of the iron removal plant and thence back to the pumping station through another 42-inch cast iron conduit. The purified water will then pass either directly to the high lift pumps for delivery to the city, or if there is a surplus, it is discharged through a concrete conduit into the main storage reservoir.
Finished Grading Plan
In the proposed finished grading about the Parkway Station, a series of drives have been laid out to give convenient access to all portions of the works and a siding from the L. and N. Railroad is provided for the delivery of coal. The station is located in a good residential district and it is proposed to make it as attractive as possible by parking the grounds and making the buildings of pleasing architectural appearance.
Reservoir and Equalizing Basin
The reservoir and equalizing basin is a reinforced concrete structure with a total capacity of about 10,000,000 gallons, but one corner is walled off, giving 1,000,000 gallons capacity for equalizing the flow from the wells. The roof is of the flat slab type of construction with panels 18 feet square and is designed for a live load of 100 lbs. per square foot in addition to the weight of the earth fill. The reservoir is to be covered with earth and finished as a level terrace on which it is proposed to construct six tennis courts.
The Pumping Station
The exterior of the building is being built of mat-face texture brick with a range of shades from gun-metal to light red laid in Flemish Bond. The corner pylons, base course, cornice and other exterior trim are of buff Bedford limestone. The interior of the pump room will be faced with light buff, Kittanning brick. Steel sash will be used throughout and as far as practicable windows have been provided to light the basement.
As will be seen by the illustration, the placing of the machinery in a double row has necessitated a clear span of about 120 feet for the pump room of the pumping station. The coal bunker is suspended from the boiler room roof trusses, which avoids the obstruction of additional supporting columns. A 15-ton electric travelling crane of 117 foot clear span will serve the pump room. There is a 12-foot basement under the pump and boiler rooms to accommodate condensers, steam piping and other auxiliaries.
(Continued on page 220)
(Continued from page 204)
Crank and Fly Wheel Pumping Engines
There arc two Snow pumping engines of the horizontal, cross compound, crank and fly wheel type with a nominal capacity of 15 m. g. d. but designed to deliver 16.5 m. g. d. continuously when necessary, the total head pumped against being 200 feet. Each unit will have a surface condenser of the water works type in the suction, attached air and condensate pumps, and a vacuum condensate heater. The valve gear is designed for steam at 200 pounds pressure and 200 degrees superheat with poppet valves on the high pressure cylinders. In view of the direct pumpage into the mains it is expected to use the crank and fly wheel units for most of the work as they will maintain good economy over wide ranges in capacity.
Turbo-Centrifugal Pumping Units
There will be two turbo-centrifugal pumping units, each consisting of a 16-inch single stage Worthington pump, gear driven by a General Electric steam turbine. The capacity of each unit is 16.5 m. g. d. against a total head of 200 feet and the turbines are designed for the same steam conditions as the crank and fly wheel pumping engines.
Each unit will have a surface condenser of the water works type in the suction with a condensate heater. The air pumps will be of the Worthington water jet type and the condensate from each unit will be handled by a centrifugal pump direct connected to a small water turbine. Pressure water from the main discharge line will drive the condensate pump turbine and then pass through the water jet air pump and be returned to the suction conduit. The resultant duty guaranteed was 144,000,000 foot pounds.
Air Compressors
The four air compressors, which are of the horizontal, cross compound, crank and fly wheel, two stage type are being built by the Nordberg Manufacturing Company. Each unit will have a capacity of 2,700 cubic feet net, of free air per minute, against a gauge pressure of 100 pounds, but will be designed to operate with maximum economy at 85 pounds pressure. The valve gear is designed for the same steam conditions as the pumping units with poppet valves on the high pressure cylinder.
Each unit will have a surface condenser with condensate heater and attached air and condensate pumps. The circulating water for the condensers will be taken from the discharge of the water turbines operating the secondary pumps. Two of the compressors will be sufficient for the maximum station load and the two other units are for reserve.
Secondary Pumping Units
The secondary pumping units, for delivering water to the aerator, are three in number, and each will consist of a horizontal, centrifugal pump direct connected to a water turbine, driven by pressure water from the high lift pumps. Both pumps and turbines are being built by the Worthington Pump and Machinery Corporation and each unit will have a nominal capacity of 9 m. g. d. against a total head of 26 feet. The overall efficiency of the pumps and turbines will be about 65 per cent, which is equivalent, in combination with the high lift pumping engines, to a duty of 93,000,000 foot pounds per 1,000,000 B. T. U. This method of pumping is therefore much more economical than the use of small steam turbine or engine driven units.
In event of a very severe conflagration it is possible to by-pass the aerator and iron removal plant and shut down these units so that the entire capacity of the high lift pumps would be available.
Boiler Plant
The boiler plant will comprise four 350 horse power, Cascv-Hedges, boilers of the horizontally inclined, water tube type with longitudinal drums built for an operating steam pressure of 225 pounds. Each boiler is to be equipped with a Foster superheater and in order to try out the practical advantage of different degrees of superheat, two units have been designed for 75 degrees superheat and the other two for 200 degrees superheat.
Each boiler will have a Sanford Riley, four retort, underfeed stoker with its own driving engine. Forced draft for each stoker is to be furnished by an electric motor driven fan and there will be a reserve fan, steam turbine driven, with air ducts so arranged that it may serve any boiler. The boilers have steel plate casings to reduce air leakage through the setting. To provide liberal combustion space the boilers have been set 12 feet above the floor. A radial brick stack 225 high with an inside top diameter of 9 feet will provide draft for the boiler plant.
General Plan of Basement
The arrangement of the elaborate header system for controlling the discharge from the high lift pumps. There are eighteen 24-inch hydraulic operated, gate valves so arranged that no single failure of either a valve or section of piping will put out of service more than one pumping unit or one force main. The hydraulic valves are all controlled from an operating table in the entrance hall of the station. Duplicate sources of pressure water are to be provided to insure operation of the valves at all times. Venturi meters arc provided on each pump discharge.
All steam and feed water piping and other important lines have in general been laid out in loops and careful study given to the location of valves and connections so as to secure the greatest reliability of service.
Duplicate 100-K. W. A. C. generators arc to be installed, each driven by a Chuse Unaflow engine to furnish 3-phasc, 60 cycle current at 240 volts for the operation of the stoker fans, coal handling equipment, crane and shop tools as well as for lighting the station.
A complete central oiling system will be installed with the necessary storage tanks, filters and other appurtenances to supply the different grades of oil required to all main units of the station equipment.
An interesting feature of the station equipment are four Thomas thermo-electric meters which will be installed, one on each main air line. These meters will accurately measure the quantity of air delivered under varying conditions of pressure and temperature and will be used to check the total air going to each group of wells as well as to determine the true delivery of the compressors during duty trials.
In order to reduce the lift from the artesian water level to the station and secure a suitable hydraulic gradient for the wells and collecting conduit it was necessary to place the pumping station at a relatively low elevation and construct the reservoir almost wholly in cut. This resulted in a surplus of over 50,000 cubic yards of material which had to be removed from the site.
Iron Removal Plant
The iron removal plant is essentially a rapid sand filter plant with a nominal capacity of 18 m. g. d. On the main floor of the plant the eight 2.25 m. g. d. filter units are arranged on two sides of a central operating gallery. In the north wing of the head-house are provided an office, toilet and locker rooms and liberal laboratory space. The south end of the head-house is occupied by a chemical room which contains duplicate dry feed lime machines and space for the storage of lime.
A reinforced concrete wash water tank, 35 feet in diameter by 10 feet in depth, with a capacity of 70,000 gallons, occupies the upper part of the head-house.
The iron removal plant, will he constructed to correspond with the pumping station. The entrance lobby, laboratory rooms, toilets, and office will have walls of impervious grey brick like the pump room and the filter and chemical rooms will be faced with buff Kittanning brick like the boiler room. The entrance lobby and operating gallery will have red quarry tile floors and the laboratories will have floors of rubber tile.
The filter tanks and pipe gallery, reinforced concrete flumes are to be used for the main influent and effluent conduits and drains. The collecting conduits beneath each filter unit are also of reinforced concrete and of relatively large size to reduce friction losses and give uniform distribution of wash water. Each filter unit is to have a central wash water trough with twelve lateral gutters, all of reinforced concrete.
The net filtering area of each filter is 825 square feet which is equivalent to practically 360 square feet per m. g. d. of rated capacity. Small case iron sleeves are to be set in the top of the main under drains, to receive the tees of the perforated lateral pipes.
The arrangements of the piping connections, valves, and controllers in the pipe gallery are such that the plant will have hydraulic valves throughout, controlled from tables on the filter operating floor and each filter unit will discharge through a Simplex rate controller.
The filter strainer system will consist of 2 1/2-inch galvanized wrought iron pipes, spaced 9 inches on centers, with special cast iron tees at the center with long spigots which will be leaded into the floor sleeves. The lateral pipes will have two 1/4-inch holes spaced every 4 inches, the holes being located 30 degrees from the center line of the bottom of the lateral. The outer ends of each lateral will have special screwed caps provided with lugs for supporting the ends of the lateral and these caps will each be tapped with two 1/4-inch holes to insure satisfactory washing of the outside edges of the filters.
Aerator, Sections, Details, and Superstructure Plan
The aerator substructure is designed in the form of a cross to give large wall area for ventilation. The well water enters through a conduit to a central riser chamber from which it is distributed through four conduits, one for each arm of the cross. The collecting conduits arc arranged to bring aerated water to a trough at the front of the structure where it can be treated with a small dose of lime to remove any residual free carbonic acid. The substructure forms a basin for the aerated water with a capacity of 240,000 gallons through which the water may circulate after the lime is applied.
The aerator units are forty in number, ten being placed in each wing of the structure. The separate units are 2 feet wide by 7 feet long giving a total area of 560 square feet. Each set of ten is arranged on both sides of a central supply conduit at the top and collecting conduit at the bottom and ample space is allowed around each unit to promote free circulation of air. The aerating units have concrete ends, supporting a distribution trough above and with notched sides to support the concrete side boards forming the aerator trays. The outlet from each unit to the collecting conduit is trapped to prevent reabsorption of carbonic acid. On both sides of each wing are provided vents in the floor leading to the outside air to facilitate the removal of the carbonic acid released from the water.
At the top there is a distributing box with concrete sides connecting with the main supply conduit. The bottom of this box is formed of No. 20 corrugated sheet brass or copper, supported on ledges in the concrete sides and also by pieces of brass pipe. This bottom is perforated with 1/8-inch holes spaced 0.8 inch apart in both directions. The aerating troughs are four in number, spaced 9 inches apart one above the other and each trough is about 10 inches in depth. They are formed of concrete side boards supported on notches in the end pieces and held in place by brass bolts. The bottoms of the troughs are constructed of 5/8-inch mesh brass wire cloth which rests on three brass pipe supports at intermediate points and at the ends is clamped to small brass angles bolted to the end pieces. All metal work of the aerator will be brass or copper on account of the corrosive action of carbonic acid. The aerating troughs are to be filled with clean crushed coke which will pass a 2-inch ring and be retained on a 1-inch ring.
Well System
The new well system will comprise 23 wells for the present installation, four of which are located on the Parkway Station site and the balance easterly along North Parkway and the L. & N. Railroad for a distance of almost two miles. The wells are in general placed about 500 feet apart to avoid undue interference. The wells have 12-inch casings and 50 feet of 10-inch brass strainer of the Cook type. It is expected to secure a yield of about one million gallons daily per well with a draw down of 25 feet and the average pumping lift from the wells to the surface is estimated at 75 feet. A larger yield per well can undoubtedly be secured in emergencies but in general it is planned to operate sufficient wells to obtain an economical draw down rather than attempt to secure the maximum capacity.
It was originally intended to place the wells on the mall in the center of the Parkway, but owing to opposition from property owners, a number of lots were bought for well locations and at the easterly end a strip of land paralleling the L. & N. Railroad was purchased. The collecting conduit and air lines are designed so that several additional wells may be added at the easterly end of the system if desired in the future.
The Well Houses
Each well house will be arranged so that a portable derrick may be mounted upon the roof when it may be necessary to work on a well. The wells will be equipped with all necessary gauges, controllers and meters so that the air lifts may be carefully regulated and operated in the most efficient manner. Considerable study is being given to the development of a tapered copper eduction pipe by means of which it is expected to materially improve the efficiency of pumping.
The entire project, which will cost about $2,800,000 is being carried out by the Memphis Artesian Water Commission, Messrs. F. G. Front, chairman; Milton J. Anderson, vicechairman, and Thomas F. Stratton, commissioner. Much credit is due to Mayor J. Rowlett Paine for getting under way this important municipal improvement. James Sheahan is general superintendent and Carl E. Davis, engineer for the commission. The works were designed by Fuller & McClintock, engineers, and are being constructed under their direction with F. G. Cunningham, resident supervising engineer.
(Excerpts from paper read at the Detroit annual convention of the American Water Works Association.)
www.fireengineering.com/articles/print/volume-74/issue-5/...
Rendering of the MLG&W Artesian Well Parkway Pumping Station now known as the Mallory Pumping Station, 488 North Dunlap St., Memphis TN - Circa 1922
How Memphis Water Works Is Planning For Future Needs
Recommended Program of Engineers—How It Is Being Carried Out— Detailed Description of Improvements—Cost Nearly Three Million
THE handling of large and important water works problems, especially when the future of a city hangs upon the proper formulation and carrying out of the program of development of its water supply, is always interesting. The following outline of the system being introduced in the water works of Memphis, Tenn., written by the engineer in charge of these developments, will be found particularly instructive. The experience of Mr. McClintock for the past seventeen years has been entirely identified with the work of George W. Fuller and the late Rudolph Hering. Mr. Fuller and Mr. McClintock have been in partnership since 1912 and from 1915 up to the present time the business has been under the firm name of Fuller & McClintock. For the past three years Mr. McClintock spent the greater portion of his time on the report of the Memphis water works project and that of Kansas City, Mo. Previous to that time he had charge of comprehensive sewer work and the sewage pumping station in the city of Toledo.
In March 1922, the writer’s firm submitted a report on the Water Supply of Memphis following a detailed investigation of the local water problem. The principal recommendations and conclusions of the report were as follows:
Recommended Program for New Supply Works
It is entirely practicable to develop a well water supply at Memphis of 75 million gallons daily or more, and there is no probability of a well designed and adequately developed artesian supply failing to meet all municipal and industrial needs during the next thirty years.
The artesian water is naturally excellent in quality, being clear, cool, soft and practically free from organic matter and bacteria. This ground water, however, contains considerable free carbonic acid, the amount ranging from 90 to 130 parts per million, which makes it highly corrosive of cast iron pipe.
The iron content of the Memphis wells varies from about 0.2 parts per million to a maximum of 6 parts per million and the high carbonic acid causes substantial amounts of iron to be dissolved as the water flows through the iron pipe system. When dissolved iron is present in quantities greater than about 0.4 parts per million it causes unsightly stains upon plumbing fixtures, kitchen utensils, and particularly white goods in the laundry. The removal of iron and carbonic acid is therefore an essential feature for a satisfactory future well supply.
It was recommended that the Auction Avenue development be abandoned as soon as new supply works could be put in service. Most of the present wells arc of such age and condition as to be of doubtful serviceability and are potentially subject to pollution. The fine sands in this vicinity preclude large yields of water being economically secured and there is grave doubt as to the continued integrity of the main tunnel and more particularly the timber lined drifts connecting with the wells. It was also deemed advisable to abandon the Central Avenue plant as soon as practicable, because it is uneconomical to operate and the site is not a good one for the further development of wells because of the distance from the ground surface to the artesian water plane.
The fourteen segregated wells are expensive to operate regularly and at times they discharge troublesome quantities of sand into the pipe system. On starting up these wells, after a shut down, objectionable amounts of rust are delivered into the mains. Some of them should prove serviceable for 8 or 10 years for emergency use during periods of high consumption, and their continued use as a reserve is perhaps advisable.
The Mississippi River has been frequently suggested as a source of water supply for Memphis and it is perfectly feasible to obtain a satisfactory filtered water supply from the river as is done at St. Louis and New Orleans. Such a supply would be much harder than the artesian water and also noticeably warmer in summer although free front iron and excessive free carbonic acid. It would be cheaper to treat the artesian supply by aeration and filtration to remove iron and carbonic acid than to remove the sediment and bacteria from the river water.
A satisfactory intake in the Mississippi River would be relatively difficult and expensive to obtain at Memphis owing to the absence of rock bottom and the shifting character of the river channel.
The investment for a river supply would be nearly twice that necessary for a complete, first class, modern, artesian water development of equal capacity and the total annual costs would be largely in excess of the corresponding annual costs for a well water supply. It was therefore recommended that the Mississippi River be dismissed from consideration as a source of supply.
The probable increase in population has been judged by the past growth of Memphis and compared with the earlier growth of similar cities. The assumed growth for Memphis is similar to that enjoyed by Cincinnati for several decades and a little higher than the growth of Louisville and New Orleans. It is not so rapid, however, as has occured in Indianapolis, Kansas City and St. Louis.
The water consumption estimates were based on the actual per capita consumption at Memphis, but for the future have been increased somewhat, as such a tendency to increase throughout a period of years is generally noted in most cities, notwithstanding all attempts to curtail waste.
The city may be arbitrarily divided into two areas designated the Eastern and Western Districts, respectively.
The plot of land in the northwest portion of the city, already owned by the water department, known as the Dunlap Street site is favorably situated for a new well water development. This site is adjacent to the North Parkway, which is an excellent location for wells, and it is also reasonably near to the more densely built up western portion of the city where the heaviest water consumption occurs. After careful study of other well projects it was determined that the most economical plan would be to develop works at Dunlap Street of sufficient capacity to provide for the full draft in the Western District for a period of 30 years or more. Such a plant would then have sufficient capacity to supply the entire city for a period of 8 or 10 years. Before the capacity of the Dunlap Street station is exceeded by the increasing consumption in the Western District, a new eastern station should be constructed at some location where the length of connecting lines to the distribution system will not be excessive, and a suitable area for sinking wells can be obtained, at which the depths from the surface to the artesian water plane is not too great for economical operation.
The new works should comprise a modern, steamoperated, high lift pumping station; a covered reservoir to equalize peak rates of water consumption and furnish a reserve for fire purposes; suitable aerating arrangements and filters for removing free carbonic acid and iron; and a new system of wells extending eastward along North Parkway for supplying this station through a suitable collecting conduit. Discharge mains should be installed to deliver the water into the present distribution system.
The free carbonic acid content is greatly reduced by the air lift method of pumping water from the wells, about 80 per cent. being removed. This was conclusively proven by experiment and by observation of air lift installations in various parts of the city. To insure against corrosion in street mains and consequent increase in iron content, the carbonic acid should be reduced to 10 parts or less, which result can best be obtained by suitable aeration through coke beds together with the application of small quantities of lime.
The iron can be readily and completely removed by passing the water through rapid sand filters at normal rates for mechanical filters and can be completely removed from fully aerated water by such means only.
The advantages of a highly polished, sparkling product from the city water works fully warrant the relatively small expense of removing the iron and carbonic acid. By carrying out these recommendations the citizens will obtain freedom from iron stains and the unusually high corrosive action of the artesian water. Memphis will then have a city water equaled by few sizeable cities in the world and surpassed by none.
The air lift is the best method for raising water from wells and delivering it to the treatment works at Dunlap Street. Electrically operated deep well pumps would be somewhat more expensive and do not showthe advantage which the air lift possesses in removing the larger part of the free carbonic acid.
As a result of the report the city decide to construct new water supply works in substantial accordance with the recommendations. Work on plans and specifications were commenced in April, 1922, and contracts for machinery let in July 1922. To date, practically all work is under contract and construction of the pumping station, pumping equipment, and other portions of the works is well advanced. It is expected that the new works will be completed and in operation early in 1924. The following is a general description of the work:
Parkway Station Layout
The water of the Parkway Station from the wells enters the equalizing basin which provides for variations between the flow from the wells and the rate of operation of the aerator and iron removal plant. From the equalizing basin the water flows to the secondary pumps in the north end of the pumping station which discharge through a 42-inch cast iron conduit to the aerator. A Venturi meter is provided in this conduit for measuring the flow of water to the aerator. After passing through the aerator the water goes through the filters of the iron removal plant and thence back to the pumping station through another 42-inch cast iron conduit. The purified water will then pass either directly to the high lift pumps for delivery to the city, or if there is a surplus, it is discharged through a concrete conduit into the main storage reservoir.
Finished Grading Plan
In the proposed finished grading about the Parkway Station, a series of drives have been laid out to give convenient access to all portions of the works and a siding from the L. and N. Railroad is provided for the delivery of coal. The station is located in a good residential district and it is proposed to make it as attractive as possible by parking the grounds and making the buildings of pleasing architectural appearance.
Reservoir and Equalizing Basin
The reservoir and equalizing basin is a reinforced concrete structure with a total capacity of about 10,000,000 gallons, but one corner is walled off, giving 1,000,000 gallons capacity for equalizing the flow from the wells. The roof is of the flat slab type of construction with panels 18 feet square and is designed for a live load of 100 lbs. per square foot in addition to the weight of the earth fill. The reservoir is to be covered with earth and finished as a level terrace on which it is proposed to construct six tennis courts.
The Pumping Station
The exterior of the building is being built of mat-face texture brick with a range of shades from gun-metal to light red laid in Flemish Bond. The corner pylons, base course, cornice and other exterior trim are of buff Bedford limestone. The interior of the pump room will be faced with light buff, Kittanning brick. Steel sash will be used throughout and as far as practicable windows have been provided to light the basement.
As will be seen by the illustration, the placing of the machinery in a double row has necessitated a clear span of about 120 feet for the pump room of the pumping station. The coal bunker is suspended from the boiler room roof trusses, which avoids the obstruction of additional supporting columns. A 15-ton electric travelling crane of 117 foot clear span will serve the pump room. There is a 12-foot basement under the pump and boiler rooms to accommodate condensers, steam piping and other auxiliaries.
(Continued on page 220)
(Continued from page 204)
Crank and Fly Wheel Pumping Engines
There arc two Snow pumping engines of the horizontal, cross compound, crank and fly wheel type with a nominal capacity of 15 m. g. d. but designed to deliver 16.5 m. g. d. continuously when necessary, the total head pumped against being 200 feet. Each unit will have a surface condenser of the water works type in the suction, attached air and condensate pumps, and a vacuum condensate heater. The valve gear is designed for steam at 200 pounds pressure and 200 degrees superheat with poppet valves on the high pressure cylinders. In view of the direct pumpage into the mains it is expected to use the crank and fly wheel units for most of the work as they will maintain good economy over wide ranges in capacity.
Turbo-Centrifugal Pumping Units
There will be two turbo-centrifugal pumping units, each consisting of a 16-inch single stage Worthington pump, gear driven by a General Electric steam turbine. The capacity of each unit is 16.5 m. g. d. against a total head of 200 feet and the turbines are designed for the same steam conditions as the crank and fly wheel pumping engines.
Each unit will have a surface condenser of the water works type in the suction with a condensate heater. The air pumps will be of the Worthington water jet type and the condensate from each unit will be handled by a centrifugal pump direct connected to a small water turbine. Pressure water from the main discharge line will drive the condensate pump turbine and then pass through the water jet air pump and be returned to the suction conduit. The resultant duty guaranteed was 144,000,000 foot pounds.
Air Compressors
The four air compressors, which are of the horizontal, cross compound, crank and fly wheel, two stage type are being built by the Nordberg Manufacturing Company. Each unit will have a capacity of 2,700 cubic feet net, of free air per minute, against a gauge pressure of 100 pounds, but will be designed to operate with maximum economy at 85 pounds pressure. The valve gear is designed for the same steam conditions as the pumping units with poppet valves on the high pressure cylinder.
Each unit will have a surface condenser with condensate heater and attached air and condensate pumps. The circulating water for the condensers will be taken from the discharge of the water turbines operating the secondary pumps. Two of the compressors will be sufficient for the maximum station load and the two other units are for reserve.
Secondary Pumping Units
The secondary pumping units, for delivering water to the aerator, are three in number, and each will consist of a horizontal, centrifugal pump direct connected to a water turbine, driven by pressure water from the high lift pumps. Both pumps and turbines are being built by the Worthington Pump and Machinery Corporation and each unit will have a nominal capacity of 9 m. g. d. against a total head of 26 feet. The overall efficiency of the pumps and turbines will be about 65 per cent, which is equivalent, in combination with the high lift pumping engines, to a duty of 93,000,000 foot pounds per 1,000,000 B. T. U. This method of pumping is therefore much more economical than the use of small steam turbine or engine driven units.
In event of a very severe conflagration it is possible to by-pass the aerator and iron removal plant and shut down these units so that the entire capacity of the high lift pumps would be available.
Boiler Plant
The boiler plant will comprise four 350 horse power, Cascv-Hedges, boilers of the horizontally inclined, water tube type with longitudinal drums built for an operating steam pressure of 225 pounds. Each boiler is to be equipped with a Foster superheater and in order to try out the practical advantage of different degrees of superheat, two units have been designed for 75 degrees superheat and the other two for 200 degrees superheat.
Each boiler will have a Sanford Riley, four retort, underfeed stoker with its own driving engine. Forced draft for each stoker is to be furnished by an electric motor driven fan and there will be a reserve fan, steam turbine driven, with air ducts so arranged that it may serve any boiler. The boilers have steel plate casings to reduce air leakage through the setting. To provide liberal combustion space the boilers have been set 12 feet above the floor. A radial brick stack 225 high with an inside top diameter of 9 feet will provide draft for the boiler plant.
General Plan of Basement
The arrangement of the elaborate header system for controlling the discharge from the high lift pumps. There are eighteen 24-inch hydraulic operated, gate valves so arranged that no single failure of either a valve or section of piping will put out of service more than one pumping unit or one force main. The hydraulic valves are all controlled from an operating table in the entrance hall of the station. Duplicate sources of pressure water are to be provided to insure operation of the valves at all times. Venturi meters arc provided on each pump discharge.
All steam and feed water piping and other important lines have in general been laid out in loops and careful study given to the location of valves and connections so as to secure the greatest reliability of service.
Duplicate 100-K. W. A. C. generators arc to be installed, each driven by a Chuse Unaflow engine to furnish 3-phasc, 60 cycle current at 240 volts for the operation of the stoker fans, coal handling equipment, crane and shop tools as well as for lighting the station.
A complete central oiling system will be installed with the necessary storage tanks, filters and other appurtenances to supply the different grades of oil required to all main units of the station equipment.
An interesting feature of the station equipment are four Thomas thermo-electric meters which will be installed, one on each main air line. These meters will accurately measure the quantity of air delivered under varying conditions of pressure and temperature and will be used to check the total air going to each group of wells as well as to determine the true delivery of the compressors during duty trials.
In order to reduce the lift from the artesian water level to the station and secure a suitable hydraulic gradient for the wells and collecting conduit it was necessary to place the pumping station at a relatively low elevation and construct the reservoir almost wholly in cut. This resulted in a surplus of over 50,000 cubic yards of material which had to be removed from the site.
Iron Removal Plant
The iron removal plant is essentially a rapid sand filter plant with a nominal capacity of 18 m. g. d. On the main floor of the plant the eight 2.25 m. g. d. filter units are arranged on two sides of a central operating gallery. In the north wing of the head-house are provided an office, toilet and locker rooms and liberal laboratory space. The south end of the head-house is occupied by a chemical room which contains duplicate dry feed lime machines and space for the storage of lime.
A reinforced concrete wash water tank, 35 feet in diameter by 10 feet in depth, with a capacity of 70,000 gallons, occupies the upper part of the head-house.
The iron removal plant, will he constructed to correspond with the pumping station. The entrance lobby, laboratory rooms, toilets, and office will have walls of impervious grey brick like the pump room and the filter and chemical rooms will be faced with buff Kittanning brick like the boiler room. The entrance lobby and operating gallery will have red quarry tile floors and the laboratories will have floors of rubber tile.
The filter tanks and pipe gallery, reinforced concrete flumes are to be used for the main influent and effluent conduits and drains. The collecting conduits beneath each filter unit are also of reinforced concrete and of relatively large size to reduce friction losses and give uniform distribution of wash water. Each filter unit is to have a central wash water trough with twelve lateral gutters, all of reinforced concrete.
The net filtering area of each filter is 825 square feet which is equivalent to practically 360 square feet per m. g. d. of rated capacity. Small case iron sleeves are to be set in the top of the main under drains, to receive the tees of the perforated lateral pipes.
The arrangements of the piping connections, valves, and controllers in the pipe gallery are such that the plant will have hydraulic valves throughout, controlled from tables on the filter operating floor and each filter unit will discharge through a Simplex rate controller.
The filter strainer system will consist of 2 1/2-inch galvanized wrought iron pipes, spaced 9 inches on centers, with special cast iron tees at the center with long spigots which will be leaded into the floor sleeves. The lateral pipes will have two 1/4-inch holes spaced every 4 inches, the holes being located 30 degrees from the center line of the bottom of the lateral. The outer ends of each lateral will have special screwed caps provided with lugs for supporting the ends of the lateral and these caps will each be tapped with two 1/4-inch holes to insure satisfactory washing of the outside edges of the filters.
Aerator, Sections, Details, and Superstructure Plan
The aerator substructure is designed in the form of a cross to give large wall area for ventilation. The well water enters through a conduit to a central riser chamber from which it is distributed through four conduits, one for each arm of the cross. The collecting conduits arc arranged to bring aerated water to a trough at the front of the structure where it can be treated with a small dose of lime to remove any residual free carbonic acid. The substructure forms a basin for the aerated water with a capacity of 240,000 gallons through which the water may circulate after the lime is applied.
The aerator units are forty in number, ten being placed in each wing of the structure. The separate units are 2 feet wide by 7 feet long giving a total area of 560 square feet. Each set of ten is arranged on both sides of a central supply conduit at the top and collecting conduit at the bottom and ample space is allowed around each unit to promote free circulation of air. The aerating units have concrete ends, supporting a distribution trough above and with notched sides to support the concrete side boards forming the aerator trays. The outlet from each unit to the collecting conduit is trapped to prevent reabsorption of carbonic acid. On both sides of each wing are provided vents in the floor leading to the outside air to facilitate the removal of the carbonic acid released from the water.
At the top there is a distributing box with concrete sides connecting with the main supply conduit. The bottom of this box is formed of No. 20 corrugated sheet brass or copper, supported on ledges in the concrete sides and also by pieces of brass pipe. This bottom is perforated with 1/8-inch holes spaced 0.8 inch apart in both directions. The aerating troughs are four in number, spaced 9 inches apart one above the other and each trough is about 10 inches in depth. They are formed of concrete side boards supported on notches in the end pieces and held in place by brass bolts. The bottoms of the troughs are constructed of 5/8-inch mesh brass wire cloth which rests on three brass pipe supports at intermediate points and at the ends is clamped to small brass angles bolted to the end pieces. All metal work of the aerator will be brass or copper on account of the corrosive action of carbonic acid. The aerating troughs are to be filled with clean crushed coke which will pass a 2-inch ring and be retained on a 1-inch ring.
Well System
The new well system will comprise 23 wells for the present installation, four of which are located on the Parkway Station site and the balance easterly along North Parkway and the L. & N. Railroad for a distance of almost two miles. The wells are in general placed about 500 feet apart to avoid undue interference. The wells have 12-inch casings and 50 feet of 10-inch brass strainer of the Cook type. It is expected to secure a yield of about one million gallons daily per well with a draw down of 25 feet and the average pumping lift from the wells to the surface is estimated at 75 feet. A larger yield per well can undoubtedly be secured in emergencies but in general it is planned to operate sufficient wells to obtain an economical draw down rather than attempt to secure the maximum capacity.
It was originally intended to place the wells on the mall in the center of the Parkway, but owing to opposition from property owners, a number of lots were bought for well locations and at the easterly end a strip of land paralleling the L. & N. Railroad was purchased. The collecting conduit and air lines are designed so that several additional wells may be added at the easterly end of the system if desired in the future.
The Well Houses
Each well house will be arranged so that a portable derrick may be mounted upon the roof when it may be necessary to work on a well. The wells will be equipped with all necessary gauges, controllers and meters so that the air lifts may be carefully regulated and operated in the most efficient manner. Considerable study is being given to the development of a tapered copper eduction pipe by means of which it is expected to materially improve the efficiency of pumping.
The entire project, which will cost about $2,800,000 is being carried out by the Memphis Artesian Water Commission, Messrs. F. G. Front, chairman; Milton J. Anderson, vicechairman, and Thomas F. Stratton, commissioner. Much credit is due to Mayor J. Rowlett Paine for getting under way this important municipal improvement. James Sheahan is general superintendent and Carl E. Davis, engineer for the commission. The works were designed by Fuller & McClintock, engineers, and are being constructed under their direction with F. G. Cunningham, resident supervising engineer.
(Excerpts from paper read at the Detroit annual convention of the American Water Works Association.)
www.fireengineering.com/articles/print/volume-74/issue-5/...