WATER SUPPLY. 



WATER SUITI.V. 



too 



the purity of the water; but if nur.ll local watercourses shouM ! 

 likely to pour into the stream, or if il.e latter should U- exposed to the 

 danger of c 



contamination from the <iut, amoke, or other impuritiea of 

 town atmoaphere, the conduit muat be oovered. The advantage of a 

 pi|* conduit oooaiata precisely in the protection it affords against such 

 accidental source* of contamination, and, generally speaking, it will be 

 found to be cheaper than a masonry conduit of ordinary dimensions. 

 Moreover, the facility the pipes furnish for the execution of reversed 

 ayphont dispenses with the necessity for the construction of costly 

 aqueduct*. It is essential to make the dimensions of the pipe some- 

 what larger than would theoretically be necessary to convey the quan- 

 tity of water required to be delivered ; because there is a danger, in 

 almost all cases, of the formation of an incrustation in the hit 

 the pipes, which would practically diminish their sectional area ; and 

 it is essential, also, to provide means for occasionally examining and 

 clearing the pipes. In all descriptions of conduits it is necessary to 

 provide stop-gates, or valves, and overflows, so as to arrest the passage 

 of the water in case of accident The material generally used for pipe- 

 conduits is cast-iron ; but glazed stone-ware is often employed with 

 success, when the water does not flow under great pressure. The 

 Bomans frequently used lead-pipes for this purpose ; but as a general 

 rule they preferred covered aqueduct*, and the Continental engineers 

 Btill adhere to this system. In the great Liverpool gravitation water- 

 works, and in the new supply to Glasgow from Loch Katrine, cast-iron 

 pipes have been exclusively used where any great differences of level 

 have been encountered. 



In the majority of cases at the present day, the water brought from 

 a distance for the supply of a town, is filtered before distribution ; and 

 this is effected in positions as close as possible to the pumping station, 

 or to the entry of the distributing mains, unless the water should be 

 so pure naturally as to allow this precaution to be dispensed with. 

 There are numerous systems of filtration in use in England, but the 

 one most generally adopted is to cause the water to pass through a 

 succession of layers of sand and gravel (increasing in coarseness from 

 above downwards) to a series of drains leading to a covered reservoir. 

 The total thickness of the filtering media is usually made from six to 

 seven feet, and the number of layers about eight or nine, the head of 

 water over the upper surface of the sand being about two feet. 

 Kngineers, however, are not unanimous iu their opinions as to the best 

 relations between the depth of the filtering media and the head of 

 water over them ; for in some cases the depth of the sand and gravel 

 is made only 4 feet 6 inches, and the working head four feet, instead 

 of the dimensions quoted above ; but evidently the degree of purity of 

 the water itself must materially affect this question. It may even 

 happen that the quality of the water may require the introduction of 

 some ingredient in the filtering media which should be able to exercise 

 a chemical influence upon the water itself ; and in some cases it has 

 been proposed to mix animal charcoal with the upper layers of sand, 

 in order to remove any organic matters ; or to mix the magnetic oxide 

 of iron with the sand when peaty matters are present; or even to 

 apply Dr. Clark's process when the bicarbonate of lime is present 

 in notable excess. Local considerations must guide the engineer in 

 his choice of the various systems; but however the water may be 

 treated in this stage of the distribution, it is absolutely necessary that 

 it should not bo exposed to the air at all after having been filtered, and 

 that it should be either at once passed into the distributing mains, or 

 be stored in covered reservoirs until wanted for use. In the construc- 

 tion of the latter, the only important observation to be made is that 

 they must be executed in such a way as to protect the water against 

 the action of light and of the sun's rays ; local facilities for the supply 

 of building materials must regulate the precise details of the construc- 

 tion itself. In some peculiar cases it is desirable to provide, in addi- 

 tion to the filters and pure water reservoirs, depositing basins, in which 

 the heavier materials, in mechanical suspension in the waters of the 

 natural source of supply, may deposit themselves; but, again, this 

 detail admits of no universal law ; and it is even to be observed that 

 the tendency of the London engineers is rather towards the suppression 

 of both depositing basins and storeage reservoirs. They make the 

 filters of Rumcient area and thickness to complete rapidly and effec- 

 tually the separation of the impurities ; and they pump the filtered 

 water at once into the distributing mains. Where storeage reservoirs 

 an used, then- dimensions may vary between the capacity required for 

 three days' consumption, when the source of supply is liable to occa- 

 sional interruptions ; and the capacity required for a few hours' supply 

 when the machinery is only subject to ordinary periods of rest or repair. 

 In the latter case it may be necessary, however, to make the machinery 

 in duplicate, or at least to keep a stock of duplicate parts. Care must 

 be taken to provide for all such service reservoirs, valve pits, overflow 

 pipes, waste weirs, scouring piU, and other conveniences for mjn.- 

 lion, cleansing, and repair. 



Unless in the cases of gravitation works, it is necessary, in all modem 

 domestic water supplies, to raise the water to such heights as to allow 

 of its distribution in the loftiest rooms of the houses situated on the 

 highest ground in the respective towns, by some description of ina- 

 /. When the quantity to be raised is small, and there is a 

 watercourse of considerable volume, and great constancy of flow, in 

 the neighbourhood, it may often be advisable to resort to hydraulic 

 power, and to ue one of the forms of water-wheel hereafter dc.- 



But it happens that water-power is exposed to frequent intemi; 

 so to speak, iu iU efficiency; and that iu summer, h> -n the largest 

 quantity of water must be raised, the power is the least, whilst in 

 winter the action of the wheels may be entirely suspended in conse- 

 quence of floods or of frost. In tnglatid, therefore, win-re coal is 

 cheap, and the use of steam-power is habitual, the latter is almost 

 always resorted to, and it certainly presents many advantages, on the 

 core of certainty of action, over all other sources of motive power. 

 In France, Germany, Switzerland, and the United States, however, 

 many water-wheels for the supply of towns are to be found ; and even 

 within a very few years London itself was dependent for a large portion 

 of its water supply upon the water-wheels of old London Bridge, 

 The towns of Toulouse, Geneva, Richmond, Va., and Philaii- 

 may be mentioned as amongst the most important of those supplied 

 with water by water-power ; and in the works lately executed by M i . 

 Hawksley, at Weymouth, a very ingenious application of the turbine 

 was made. The majority of the English towns are supplied by mean* 

 of (team-engines ; and the machinery lately erected for the supply of 

 London may be cited as being the most extensive and the most beauti- 

 ful of any hitherto erected. It is usually considered that there are 

 advantages in the use of the Cornish pumping engines when the power 

 to be exercised exceeds 25 horses, and that for lower powers direct- 

 acting engines, or fly-wheel engines, are preferable ; but the remark- 

 able results obtained by Messrs. Simpson and Boulton and Watt, show 

 that the preference for large Cornish engines is at least open to 

 1 question. 



In estimating the power to be provided, and consequently in de- 

 ciding the description of engine to be employed it is necessary to take 

 into account the weight of the water to be raised at the maximum 

 rate of consumption ; the total height to which it has to be raised : and 

 the various causes of retardation of flow in the pumping main, from 

 the friction upon the sides of the pipes, and the bends or changes of 

 horizontal or vertical direction. It will be necessary to revert to the 

 general laws affecting the flow of water in pipes; but here it is suffi- 

 cient to observe that an allowance equivalent to an increase of 12 feet 

 per mile in length of main, to the total weight to be lifted, is sufficient 

 to cover the effect of these retarding causes. Aa the various classes of 

 engines do not work up to their full power, calculated theoretically, it 

 is necessary to affect the result of the above method of ascertaining 

 the pumping power by the coefficients, of the respective engines ; which 

 are, for steam-power, on the average, 85, and for the best water- 

 wheels, 076. 



In small pumping engines it is found that the most useful action is 

 obtained when the power is exercised equably and continuously ; and 

 in order to secure this result, the main thaft is made to carry three 

 cranks placed at angles of 120 from each other, upon which the pump 

 rods are keyed. In the larger engines it seems that the most favourable 

 conditions of motion in the pumps are, that they should begin by 

 raising the load rapidly, in order to overcome ita vis inertia | 

 that when the motion of the ascensional column has been once esta- 

 blished, the effort of the motive power should gradually be diminished. 

 These objects are effected in the Cornish engines by introducing steam 

 to the underside of the cylinders, through large openings, at high pres- 

 sures ; the steam is then cut off when the inertia of the water has been 

 overcome, and it is allowed to expand during the remainder of the 

 stroke, exercising in so expanding sufficient power to maintain the ascen- 

 sional movement ; the return stroke is made by the dead weight of 

 the plunger and of the rods. The initial pressure of these engines is 

 usually from 24 to 3 atmospheres ; the expansion begins at from i to J 

 of the stroke of the piston ; and at the end of the stroke the pressure 

 of steam is not more than between jjj and f 6 of an atmosphere ; engines 

 so worked being said to produce a duty equivalent to about 90,000,000 

 Ibs. raised 1 foot high by the combustion of 1 cwt. of coal. But it is 

 to be observed, that in consequence of the interposition of the air-vessel 

 upon the delivery-pipe of a town putnping-cugine, the delivery is, in 

 fact, constant; and it is probable that the extraordinary results ob- 

 tained of late by the application of the beam and fly-wheel engine, on 

 a large scale, to pumping operations, may be explained by the fact that 

 as they supply water to the air-vessel iu a more continuous manner 

 than the Cornish engines do, they allow the air-vessel to produce its 

 effect with greater regularity. In the large engines erected by Messrs. 

 Simpson for the Chelsea and Lambeth Water-works, the steam works 

 at high pressure in the first of two cylinders, and at low pressure iu 

 the second ; there is a beam and fly-wheel to each engine ; and it is 

 said that the duty they perform sometimes reaches 120,000,000 Hw. 

 raised one foot high by the combustion of 1 cwt. of coal. Fly-wheel 

 engines, it may be added, possess this great advantage over Cornish 

 engines for the purpose of town distributions, namely, that they are 

 capable of being worked at more variable rates of delivery than are 

 the latter ; and in a town delivery the rate of consumption is subject 

 to such singular irregularities, that this susceptibility of variation in 

 the power may often be a matter of importance. But again, it must 

 be stated that the best modern Cornish engines have been so carefully 

 and skilfully constructed, that they have even allowed the regulating 

 service reservoirs to be dispensed with ; and both the Kent and the 

 East London Water works pump directly into their supply mains by 

 night and by day, trusting entirely to the skill of the engine-drivers to 

 adapt the motive power to the variable conditions of the consumption 



