Scour-out pipes, 10 cm. (4 in.) and 15 cm. (6 in.) in diameter, are placed in various parts of the system, draining to the sewers. Air-valves, both double and single, are also placed at high points in different parts of the system. _Reducing Valves._--At four points in the system the mains are arranged so that the supply can be interchangeable. Fig. 15 shows the arrangement of the mains at the junction of Cinco de Mayo and Alvarez Streets, and is typical of the arrangement at the other points. Each reducing valve is placed on a 30-cm. (12-in.) branch main between the two services. These valves adjust themselves automatically to the pressure required, after they have been properly regulated to the different pressures on either side. To allow repairs to be easily made, there are ordinary gate-valves at each end enclosed in the same pit. If necessary, as in case of fire, any part of the system can be changed into high pressure temporarily by closing the valves against the San Geronimo supply. Table 9 gives the length of the mains as laid, and the number of valves. TABLE 9.--LENGTH OF WATER MAINS. =========================+=====================+============= DIAMETER: | | --------------+----------+ Length, in meters. | Number of Centimeters. | Inches. | | gate-valves. --------------+----------+---------------------+------------- 10.2 | 4 | 49,831.68 | 677 15.2 | 6 | 31,918.31 | 306 30.5 | 12 | 14,461.31 | 117 38.1 | 15 | 1,661.98 | 11 45.7 | 18 | 4,522.61 | 5 61.0 | 24 | 2,826.54 | 10 76.2 | 30 | 1,454.40 | --------------+----------+---------------------+------------- Totals | 106,676.83 | 1,126 =========================+=====================+============= The pipes were all cast according to the British Standard Specification, in 3.65-m. (12-ft.) lengths, and were supplied by Messrs. D. Y. Stewart and Company, and Messrs. Dick, Kerr and Company, of Kilmarnock and London. The valves were all of standard design, faced with gun-metal, and were supplied by Messrs. Glenfield and Kennedy, Limited, of Kilmarnock, Scotland. In the distribution system it is proposed to provide 200 fire-hydrants, by arrangement with the municipality, but only a few of these have been placed. The general type is a double hydrant for two 63.5-mm. (2-1/2-in.) streams. These are to be placed at the corner of every block in the business portion of the city; single-way hydrants will be used in the residential districts.