230

MODERN STEAM PRACTICE.

The Crossness Reservoir and Pumping Station .—The sewage onthe south side of the Thames is discharged into the river at thetime of high water only; but the sewer is at such a level that it candischarge its full volume by gravitation about the time of low water.Its outlet is ordinarily closed by a pen stock placed across itsmouth, and its contents are raised by pumping into the reservoir,which is built at the same level as that on the north side, and, likeit, retains the sewage, except during the two hours of dischargeafter high water. The sewage is thus diverted from its direct courseto the river into a side channel leading to the pump well, whichforms the lower part of the engine building; from this well it islifted by four condensing rotative beam engines, each 125 horse-power, working direct from the beam two compound pumps, eachwith four plungers. The cylinders are 4 feet in diameter, with alength of stroke of 9 feet; they are situate at the end of the mainbeam, which is 40 feet in length, the crank shaft connecting rod beingattached to the farther end, and the pump rods situated on eitherside of the beam centre. The air, feed, and cold-water pumps areworked by a separate or counter beam, fixed at one end to a rock-ing lever, and attached at the other end to the main beam. Thecylinders are supplied by twelve Cornish boilers, each 6 feet indiameter and 30 feet long, with an internal furnace and flue 3 feetin diameter, set so as to have the second heat carried with a splitdraught along the sides, and the third heat under the bottom of theboiler, into the main flue leading to the chimney. The maximumquantity of sewage ordinarily requiring to be lifted by these enginesis about 10,000 cubic feet per minute; but during the night thatquantity will be considerably reduced, and, on the other hand, itwill be nearly doubled on occasions of heavy rainfall. The lift alsowill vary from 10 to 30 feet, according to the level of water in thesewer and in the reservoir into which it is lifted. These variableconditions led to some difficulty in the working, but which has beenovercome by an arrangement of the pump plungers. The pumps,which are single-acting, are placed equidistant on each side of thebeam centre, their cases being each 12 feet in diameter, and fittedwith four plungers 4 feet 6 inches in diameter. These plungers areplaced in pairs, each pair being worked from a crosshead on themain beam, which is in two flitches for this purpose, and eitherpair of plungers can be thrown out of gear. By this means thecapacity of the pumps may be varied in the proportion of one, two,