AT ARAPUNI

Wanganui Chronicle, Volume 71, Issue 237, 6 October 1928, Page 7

AT ARAPUNI

RAPID PROGRESS POWER-HOUSE FRAME UP The Arapuni hydro-electric works about which the prophets of woe have of late observed a silence that is not without its eloquence, are progressing at a rate which gives every promise that >ne of the generators will be in operation during next winter, states the New Zealand Herald. Its output of power will be 15,000 kilowatts, which is greater than tho maximum capacity of tho Horahora ntion. Naturally it is impossible to give a definite date when the power will be available, the chief source of uncertainty being the condition cf the generating machinery which has now been packed for three years. It may be found that ‘ ilations may require renewal, but, in any case, with reasonable luck, No. 3 generator sho’ be at work during the winter, and it will not be the fault of the Public Works Department if it does not come in in time to meet the winter demand. The difficulties of laying the foundations of the power-house arc now a memory and actually the extremely porous bank between the river-bed and t c excavation which had to be grouted with liquid cement before the place could be unwatered is now being cut away. Labyrinth of Concrete An idea of the progress that has been made with No. 3 generator may be gathered from the fact that the men are now working 35ft. above the bottom of the draught tube which is to carry away the water. This ’evel is 6ft. or Bft. below what will be the floor of the power-house on which those who attend the opening ceremony will walk and admire the huge machine and gaze perplexed at the switch-boards. It is the most complicated as far as concrete work is concerned. It is a maze of tunnels, ducts, channels and galleries and no fewer than carpenters, working in ree shifts and aided by circular saw, are required to provide the wood mouldings. Extremely elaborate woodwork is required. For instance, there has to be supplied for each generator a ventilating tunnel, 7ft. lOin. by sft. 3in., and the mould for the one for No. 3 is, perhaps, 59ft. long with s veral curves. Narrow, dressed timber has to be use for the walls and unle one knew the purposes of these queer structures one -right guess they were part of an ogre’s dungeon in an amusement park. The concrete \ stem is a labyrinth, the complicated nature of which could not be imagined by a lay mind. Valve Being Installed. The penstock for this set has been . tended from the cliff face and the Johnson-Larner valve is at present being installed. Its casing is 16ft. in diameter. The turbine casing, of course,

lias been set up and concreted in. The next step will be to put in the runner or spinning part, which will weigh 100 tons. The heaviest part of it will be 13 tons, which is beyond the capacity of the crane that has so far been employed, but there will be no delay because the 100-ton travelling crane, which itself weighs 70 tons, is already in position. The atcel columns of the frame of the building are 70ft. high and 20 out of the 22 are up, and most of the roof trusses, which have a span of 40ft., are in position. Two more bays at the north end of the building will complete the frame and as soon as there is covering over No. 3 set, which will be completed in about two weeks, the huge crane will be picking up its heavy burdens and carrying them to the point of assembly. The main columns of the frame weigh five tons and the roof trusses two and a-half tons. The total weight of the structural steel in the frame is 400 tons and that of the reinforcing steel is 300 tons. One generating set will have a total weight of 400 tons. Excavating the Tail Race Before the generator can start, the tail race must be ready. This implies the excavation of 50,000 cubic yards, equivalent to 70,000 tons of rock and other spoil from the old river-bed. A considerable amount of this work has already been done. There is no space for its disposal anywhere but on the banks, and three live-toils cranes are working 24 hours a day hoisting it up. It is an arresting sight to see truck tracks in the bed of the gorge where, until the gates of the diversion tunnel were closed, the Waikato River roared and foamed. Along one of these tracks a horse placidly pulls his load to the arm of one of the cranes, and in a few pools which still remain, trout and eels swim about, and already are looking for the breadcrumbs the workers throw to them at lunchtime.

The whole of the bank at the powerhouse will have to go, and outside the old bed, already squared off and levelled to a considerable width, will have to go down another Bft. to give free discharge to the water which has delivered up its power in the turbines. Expedition with this excavation was made possible by the installation of a 100 h.p. 14in. centrifugal pump at the sand bar thrown across the river course at the point where the diverted river regains it. The recent rains however, caused a backing up of the water, in spite of the pumping, and so another lOin. pump, driven by a 60 h.p. motor, was installed, and, with a total discharge of 6000 gallons a minute, the level has been lowered, enabling the excavation to proceed without hindrance. The convenience of electric power is strikingly demonstratd by these pumps. Perched on a little point of rock, where there is space only for a short jockey pulley drive, they work day in and day out. their only tender being little raft of oil drums, on which ar outboard motor is attached, and, even if its speed is three, knots, it is adequate. Without the electric cable, a steam engine would have had to be employed, and, in the position, fuelling would have been a serious matter.