Part 5 (1/2)

The extra cost of the sewers to carry the additional quantity of stor out and preparing estimates for the alternative schemes

The actual cost of the fuel allons The annual works and capital charges, exclusive of fuel, should be divided by the nore pumped per annum, rather than by the maximum quantity which the pu the whole ties allons, which es, 1-1/2 d per 1,000 gallons Even if the extra cost of enlarging the sewers is added to this sum it will still be considerably below the su a separate system for the surface water

Unless it is pere to have a free outlet to the sea at all states of the tide, the provision of effective storm overflows is a matter of supreme importance

Not only is it necessary for them to be constructed in well- considered positions, but theyone side of a manhole and parallel to the sewer is rarely efficient, as in times of storm the liquid in the sewer travels at a considerable velocity, and the greater portion of it, which should be diverted, rushes past the weir and continues to flow in the sewer; and if, as is frequently the case, it is desirable that the overflowing liquid should be screened, and vertical bars are fixed on the weir for the purpose, they block the outlet and render the overflow practically useless

Leap weir overflows are theoreticallytimes of storm, but in practice they rarely prove satisfactory This is not the fault of the system, but is, in theThe general arrange 17 In nor the pipe A falls down the ra the sewer B; when the flow is increased during store froh C, and thence along the storm-water sewer D In order that it should be effective the first step is to ascertain accurately the gradient of the sewer above the proposed overflow, then, the size being known, it is easy to calculate the velocity of flow for the varying depths of sewage corresponding with e dry weather flow, maximum dry weather flow, and six times the dry weather flow

The natural curve which the seould follow in its doard path as it flowed out from the end of the sewer can then be drawn out for the various depths, taking into account the fact that the velocity at the invert and sides of the sewer is less than the average velocity of flow The ramp should be built in accordance with the calculated curves so as to avoid splashi+ng as far as possible, and the level of the trough C fixed so that when it is placed sufficiently far from A to allow the dry weather flow to pass down the ramp it will at the same time catch the storard must be had to the altered circurowth of population occurs, for which provision is made in the scheh C is movable, so that the width of the leap weir may be adjusted from time to time as required The overflow should be frequently inspected, and the accuh, because sticks and siht down by the seill probably leap the weir instead of flowing down the rae It is undesirable to fix a screen in conjunction with this overflow, but if screening is essential the operation should be carried out in a special manhole built lower down the course of the storm-water sewer Considerable wear takes place on the ramp, which should, therefore, be constructed of blue Staffordshi+re or other hard bricks The ramp should ter water, and the stones which ht with it, which would crack stoneware pipes if such were used

In cases where it is not convenient to arrange a sudden drop in the invert of the sewer as is required for a leap weir overflow, the excess flow of store 18 [Footnote: PLATE IV] In this case calculations e will flow in the pipes at the tiives the level of the lip of the diverting plate The ordinary sewage floill pass steadily along the invert of the sewer under the plate until it rises up to that height, when the opening beco capacity beco freely This restricts the flow of the sewage, and causes it to head up on the upper side of the overflow in an endeavour to force through the orifice the sa in the sewer, but as it rises the velocity carries the upper layer of the water forward up the diverting plate and thence into the storovern the direction of flow at the tih is ht above the invert can be increased easily, as ement the storm-water can easily be screened before it is allowed to pass out by fixing an inclined screen in the position shown in Fig 18 [Footnote: PLATE IV] It is loose, as is the trough, and both can be lifted out when it is desired to have access to the invert of the sewer The screen is self- cleansing, as any floating ainst it does not stop on it and reduce its discharging capacity, but is gradually dran by the flow of the sewage towards the diverting plate under which it will be carried The heavierthe invert will pass under the plate and be carried through to the outfall works, instead of escaping by the overflow, and perhaps creating a nuisance at that point

CHAPTER IX

WIND AND WINDMILLS

In s is necessary the aive his whole attention to the pu station is so much in excess of the cost of power and the sum required for the repays that it is desirable for the econoes bill as far as possible If oil or gas engines are eether while the , as for instance during the night, he must be prepared to start the pumps at very short notice, should a heavy rain storm increase the flow in the sewers to such an extent that the pue tank becoe floats whereby the puine by means of a friction clutch, so that when the level of the sewage in the puhest point desired the pump may be started, and when it is lowered to a predetermined loater level the puine in the sah the floats are a useful accessory to the plant during the tee they will not obviate his more or less constant attendance An electric motor may be controlled by a float, but in ear, probably caused by its exposure to the damp air In all cases an alarm float should be fixed, which would rise as the depth of the sewage in the pump well increased, until the top water level was reached, when the float wouldwarning bell, which could be placed either at the pu the bell the man would know the pump as full, and that he -station and start the pu would be flooded If compressed air is available a hooter could be fixed, which would be heard for a considerable distance from the station

[Illustration: PLATE IV

”DIVERTING PLATE” OVERFLOW

To face page 66]

It is apparent, therefore, that a pu machine is wanted which ork continuously without attention, and will not wasteto puht be harnessed to give this result--water and wind The use of water on such a small scale is rarely economically practicable, as even if the water is available in the vicinity of the puenerally to be executed at the point of supply, not only to store the water in sufficient bulk at such a level that it can be usefully employed, but also to lead it to the power-house, and then to provide for its escape after it has done its work The power-house, with its turbines and other e outlay, but if the pump can be directly driven from the turbines, so that the cost of attendance is reduced to a minimum, the systeh the wind is always available in every district, it is more frequent and powerful on the coast than inland The velocity of the wind is ever varying within wide lie hourly velocity, it is not constant even for oneof a wheel composed of a number of short sails fixed to a steel framework upon a braced steel tower, have been used forwater for domestic use In a very few cases it has been utilised for pue, but there is no reason why, under proper conditions, it should not be ereater extent The reliability of the wind for pu table, No 11, which were observed in Bired in order corresponding with the nitude of the annual rainfall:--

TABLE No 11

MEAN HOURLY VELOCITY OF WIND

Reference | Rainfall |Nu which the mean | Number | for |hourly velocity of the as below | | year | 6 mph | 10 mph | 15 mph | 20 mph | ----------+----------+----------+-----------+-----------+-----------+ 1 3386 16 88 220 314 2 2912 15 120 260 334 3 2886 39 133 263 336 4 2656 36 126 247 323 5 2651 34 149 258 330 6 2602 34 132 262 333 7 2516 33 151 276 332 8 2267 46 155 272 329 9 2230 26 130 253 337 10 2194 37 133 276 330 ----------+----------+----------+-----------+-----------+-----------+ Average 314 1317 2507 3308

It ures for the two years included in the foregoing table, which had the least and theset out in the following table:

TABLE No 12

MONTHLY analYSIS OF WIND

Nu which the mean velocity of the as respectively below the value mentioned hereunder

Month | Year of least wind (No 8) | Year of most wind (No 8) | | 5 10 15 20 | 5 10 15 20 | | mph mph mph mph | mph mph mph mph | ------+-------+-----+-------+-------+-------+------+------+-------+ Jan 5 11 23 27 3 6 15 23 Feb 5 19 23 28 0 2 8 16 Mar 5 10 20 23 0 1 11 18 April 6 16 23 28 1 7 16 26 May 1 14 24 30 3 11 24 31 June 1 12 22 26 1 10 21 27 July 8 18 29 31 1 12 25 29 Aug 2 9 23 30 1 9 18 30 Sept 1 13 25 30 1 12 24 28 Oct 5 17 21 26 0 4 16 29 Nov 6 11 20 26 3 7 19 28 Dec 1 5 19 24 2 7 23 29 ------+-------+-----+-------+-------+-------+------+------+-------+ Total 46 155 272 329 16 88 220 314

During the year of least wind there were only eight separate occasions upon which the average hourly velocity of the as less than six miles per hour for two consecutive days, and on two occasions only was it less than six miles per hour on three consecutive days It must be remembered, however, that this does not by anysuch days the wind did not rise above six miles per hour, and the probability is that a mill which could be actuated by a six- part of the tireatest differences between these two years occur in the figures relating to the light winds The number of days upon which the mean hourly velocity of the wind exceeds twenty miles per hour rereatest difficulty in connection with pue is the influx of storm water in times of rain, it will be useful to notice the rainfall at those tiures (Table No 13) it will be seen that, generally speaking, when there is very little wind there is very little rain Taking the ten years enumerated in Table No 11, we find that out of the 314 days on which the wind averaged less than six ht of theed l3 in on those days