224

MODERN STEAM PRACTICE.

is fitted to prevent the return of the water if the engine is stopped ora pipe bursts. In the case of the latter accident it is of importanceto prevent much water escaping, as the pipe is laid for some distancealong a railway embankment formed of gravel and sand, easilywashed away. Düring the testing of the main one pipe burst wherethere had been a chill in the casting, but so little water came outas to do but little damage to the embankment. The engine stoppedbecause of the sudden drop of the pressure acting on the catchalready referred to; and the return of the water was prevented bythe back valves, even the water between the burst and the nextvalve placed above being retained, as no air could get in except ingulps at the break.

Many things which were once considered necessary to the safetyof water-works are now superseded. The constant System, or onereservoir for the whole town, instead of each customer having onefor himself, has caused great change. Instead of the supply pipesbeing led off small pipes called “ riders,” they are put direct intothe main, and all the ends of the main are connected, so as to givegreater circulation to the water. The use of cisterns is discouragedas much as possible, as they are likely to deteriorate the quality ofthe water. Separate pipes to the reservoir—one to pump throughand the other to supply through—are not used, but only one pipefor both purposes.

It offen happens that the supply is obtained from a spot betweenthe town and the high ground where the reservoir can be made:one pipe from the reservoir is then found sufficient, and the enginepumps into it. If the town, as in the middle of the day, requiresall the water, it is sent direct into it; when the demand falls off, itis partly delivered into the reservoir; if there is an extraordinarydemand, both the reservoir and engines supply the town. By thisarrangement one main answers, and it may be much smaller thanif two were used, one to the reservoir and another from it to thetown. Much of the water, also, is pumped at a less pressure thanwould be needed to pump it entirely into the reservoir.

Stand pipes may be considered as among the precautionary con-trivances once deemed requisite for supplying water to a town; butthe supply can be obtained direct from an engine as easily andsafely by properly loaded valves, although it is found a more expen-sive plan. The engines do wretched duty, as the calls upon themare so irregulär. An engine always does best when working regu-