Model Municipal Works for a Small Town

Progress, Volume VIII, Issue 10, 1 June 1913, Page 521

Model Municipal Works for a Small Town

The Electric Lighting, Water Supply and Sewerage Schemes of Mangaweka

No city of the Incas could have been better protected by the walls of Nature from invasion of the outside world, than is the rising township of Mangaweka (or, more correctly named, Manga-Te-weka, which, if literally translated from Maori, means “Black Wood-hen”), for, by tunnel it has to be approached, and by tunnel the traveller by rail has to make his exit from the smiling valley in which the township nestles. On the other side of the valley, the Rangitikei River presents its unscalable cliffs over 300 feet in height, and, still further beyond, lie the snow-clad ranges of the Ruahines. But Nature’s walls have not been sufficient to hold back the tide of civilisation, or to repulse the advance of the Pioneer, for, less than 20 years ago, a railway engineering survey party scaled the mountains and pegged out its camp in the valley below, preparatory to the making of the iron road which links Wellington with Auckland. “Three Log Cabin” was the name assigned to the embryo from which Mangaweka, now a town of over 600 inhabitants, has grown within 16 years, and, the first settler, who had to cut his way through the bush, little thought that, on this plateau, 200 feet above the level of the Rangitikei River, would arise stores, hotels, factories, churches, and private residences, demanding modern systems of lighting, water supply and sanitation. Ear less was it in the minds of the designer of the “Rateau” high lift turbine pump, and of the workmen employed in the making of it. at the British Westinghouse factory near Manchester, that one of the finest of these pumps (which embody the best and most recent engineering practice and skill), would be installed in the furthest distant part of the Empire for the purpose of providing a plentiful supply of water to the inhabitants of one of the rising towns of New Zealand.

A description of the works at Mangaweka will be of particular interest to our readers, as the engineering difficulties which have been overcome are quite unique in themselves, and. as these works have proved a thorough success, it leads us to believe there are few towns in New Zealand but which could be lighted efficiently by electricity and have electric power for heating, pumping, or other motive purposes. Whether or not the power be developed from waterfalls, Diesel engines, or gas engines, is a matter for investigation by competent engineers, equipped with modern experience and sound ideas on the question of finance..

In the case of Mangaweka, it is fortunate that the Mangawharariki, a tributary of the Rangitikei River, was available for hydro-electric power purposes, and, some two years ago, the Town Board instructed Mr. S. Blackley, A.M.1.E.E., chief engineer of Messrs. Turnbull and Jones, Ltd., to report on the possibilities of electric lighting, water supply, and sewerage. The report, being a favourable one, a loan of £IO,OOO was raised, and the whole of the works placed in the hands of Messrs. Turnbull and Jones, Ltd. In order to secure the maximum power necessary for the town’s requirements for many years to come, a dam was designed and erected which raised the level of the water in the Mangawharariki stream about thirty feet at the flume intake, and a

spillway, fifty-two feet wide, was provided above the flume level. The dam is shown in Fig. No. 7, and is of sufficient dimensions to store the whole of the water flowing in the Mangawharariki during twenty-four hours at normal summer level, the storage capacity being just under five million gallons of water, so that 75 h.p. can be developed for eight consecutive hours every day. One abutment of the dam had to be carried 60 feet into the cliff, owing to faulty strata. The dam is situated about 300 yards from where the Mangawharariki joins the Rangitikei river. It is designed on the gravity princple, is 35 feet in height, and is strengthened by arch action to withstand the exceptional floods which are characteristic of all Rangitikei streams. Two underflow sluice gates are operated from the bridge. Through another gate, the water is turned on to the fluming, which is constructed according to the latest hydro-electric design as used in recent American schemes, and is built of heart of totara. The fluming is of sufficient size for double the horse-power developed at present in the power house. A view of the fluming is given in Fig. 6.

The power house, shown in Fig. 1, is a building 25ft. x 17ft. 6in., and has been arranged so that another turbine set can be installed at a minimum of expense whenever the demand for extra power justifies the extension.

The water is conveyed from the fluming through a large inlet pipe 36 inches in diameter to a Boving vertical turbine of 45 brake horse-power running at a speed of 675 revolutions per minute. This turbine plant possesses some quite unusual features, as provision had to be made to safeguard against the extraordinary flood range of the Rangitikei River. Over 29 feet rise was recorded on 17th April, 1897, and the consulting engineers. Messrs. Turnbull and Jones, Ltd.., considered that although such a high flood might never occur again, it would not be good engineering practice to place this important and valuable plant within the flood range. The floor level has, therefore, been kept up Ift. 6in. above the record flood level, and means have been taken in the design of the plant to secure all the working head available. * This is achieved by using a long draft tube set in concrete, and run from the turbine casing into the old course of the Mangawharariki. By this means a total head of about 37| feet is secured, giving a maximum power of nearly 45 b.h.p. The vertical shaft of the turbine is connected through beautifully cut double helical bevel gearing to the horizontal shaft to which the flywheel, alternator, and exciter are attached. This horizontal shaft runs at a speed of 1,000 revolutions per minute, generating 25 kilowatts on the 3-phase alternator at 50 cycles and 2,400 volts.

The Alternator, shown in Fig. 5, is of the rotating field type, and was supplied by the Britisn Westinghouse Electric and Manufacturing Co., Ltd., of Manchester, as was also the high tension switchboard which controls the electrical machinery and the overhead supply lines which run to the pump house and as far as the railway station. The speed of the turbine and alternator is controlled in an almost human way by an automatic oil pressure governor, supplied by Messrs. J. 0. Boving and Co., of London.

A time switch cut-out arrangement is prowled to shut off the water from the turbine, automatically, at any pre-determinei hour during the night. At present the plant is closed down automatically at 12 midnight.

The switchboard is shown in Fig. 9, and is fitted with all the necessary controlling apparatus and provided with lightning arresters.

About half a mile distant, and on the other side of the Rangitikei River from the power station, is situated the pump house shown in Fig. 4. Here, again, provision has had to be made for the extraordinary flood range of the Rangitikei. The walls of the building have been erected in ferroconcrete 2ft. thick at the base and tapering to 9in. at the top. The inside dimensions are 14ft. x 10ft., and a 30ft. tunnel, 4ft. high x 3ft. wide, lined with concrete, conducts the water from the Rangitikei River .to the 18ft. vertical suction pipe connected to the electrically driven pump. The highest ordinary flood level comes to within a few inches of the foundations of the pump house and 14ft. above the normal summer level of the Rangitikei. The walls

of the pump house are sufficiently high and strong to protect the pumping plant from any danger from flood up to the level of the extraordinary flood of 1897.

The Westinghouse Rateau High-lift Pump, illustrated on page 521, is designed to deliver 4,800 gallons of water per hour against a total head of 425 ft., and is direct connected through a flexible coupling to a 3-phase British Westinghouse Squirrel Cage Induction type motor running on a voltage of 2,200, and at the enormous speed of 2,880 revolutions per minute. This turbine pump discharges into the Sin. rising main, which connects with the water supply reservoir and the 24 h.p. motor, which drives it is controlled through high tension oil switches, and is protected against lightning by lightning arresters, fixed on the end wall of the pump house.

The water supply reservoir is 180 ft. above the level of the town itself, and gives an excellent water pressure for fire purposes. The reservoir is constructed of reinforced concrete and divided into two sections, each of which has a capacity of 50,000 gallons of water, which should be ample for the. requirements of Mangaweka for many years to come. By a simple arrangement of valves, the pump can be made to discharge into either section of the reservoir and each section can be used separately so as to allow for the settling of any sediment, and for emptying at any time without interfering with the town supply. The reticulation mains from the reservoir consist of 6in. and 4in. Mannesmann steel pipes, provided with fire plugs and sluice valves. The extension of the water mains will shortly be made to the railway station, and a contract has been entered into between the Railway Department and the Town Board for the supply of about 10,000 gallons of water per day.

A telephone system connects the power station with the pump house and Town Board offices, and the necessary precautions have been taken to prevent any danger through the telephone line coming in contact with the high tension transmission lines carried on the same poles.

It is interesting to note that the overhead lines consist of aluminium stranded cable, which is supported on insulators carried on totara or Australian hardwood naturally round poles. These poles are erected in all the principal streets, and extend as far as the railway station. Fifty electric lamps of 100 c.p., with a special type of reflector, have been provided for the lighting of the streets, and these lights, as well as the private reticulation, are controlled from a distributor pillar fixed on a pole abou. the centre of the town. This pillar is fed from a 15 k.w. 3-phase transformer, which reduces the voltage from 2200 to 400 volts across the outers and 230 volts between any one phase and the neutral point of the transformer.

The 400 volts will be used for power purposes and the lighting and heating supply will be balanced on the 230 volts. At the railway station end of the line, a 5 k.w. transformer has been erected in anticipation of a demand for lighting or power purposes.

A high-class gravity sanitary system is provided in the main part of the town.