FIG. 64. ARRANGEMENT OF PIPING RECOMMENDED AS BEST FOR PASSENGER CAR STORAGE YARD.
Such a layout must be at once dismissed as impractical, and some other arrangement must be adapted. The arrangement of piping shown in [Fig. 64] is considered by the author to be the best that can be devised for this case.
With this arrangement the vacuum at the separator must be maintained at 11.50 in. mercury to insure a vacuum of 6 in. mercury at the outlet “x” under the most unfavorable conditions, and the maximum variation in vacuum at the inlets will be 3.45 in. mercury when 1¹⁄₄-in. hose is used. This will give a maximum vacuum under a carpet renovator of 7¹⁄₂ in. mercury with 37 cu. ft. of air passing and will permit 70 cu. ft. of free air per minute to pass a brush renovator when operating with 100 ft. of hose attached to the inlet at which the highest vacuum is maintained. Both of these conditions will permit satisfactory operation and the increased air quantities will not seriously affect the calculations already made. The maximum horse power required at the separator will now be 20.5 as against over 50 in the case of the piping arrangement shown in [Fig. 63], and will require an exhauster having a displacement of 950 cu. ft. instead of 1,800 cu. ft. required with the former layout.
If 1-in. hose is used and 10 in. mercury maintained at the outlet “x” under the same conditions as before, the vacuum at the separator will be 14.50 in. and the maximum variation in the vacuum at the inlets will be 3 in., which will give a maximum vacuum under a carpet renovator of 6 in. mercury with 32 cu. ft. of air passing and will permit the passage of 45 cu. ft. of free air through a brush renovator when operated at the end of 100 ft. of hose attached to the outlet at which the highest vacuum is maintained. This is a more uniform result, than was noted when 1¹⁄₄-in. hose was used.
The maximum horse power which will be required at the separator will now be 18.6 and the maximum displacement in the exhauster will be 740 cu. ft.
It is, therefore, evident that, where very long runs of piping are necessary and where 100 ft. of hose will always be necessary, the use of 1-in. hose will require less power and a smaller displacement exhauster than would be required with 1¹⁄₄-in. hose, without affecting the efficiency of the cleaning operations, and at the same time rendering the operation of the renovators on extreme ends of the system more uniform.
The example cited in [Figs. 63] and [64] is not by any means an extreme case to be met in cleaning systems for car yards, and the larger the system the greater will be the economy obtained with 1-in. hose.
Such conditions, however, are confined almost entirely to layouts of this character and will seldom be met in layouts within any single building. This is fortunate, as the train cleaning is practically the only place where the use of 100 ft. of hose can be assured at all times.
Very tall buildings offer a similar condition although the laterals are now vertical and can be kept large enough to sufficiently reduce the friction without danger of deposit of dirt in them, and the horizontal branches will be short and also large enough to keep the friction within reasonable limits without danger of deposit of dust.
Where large areas within one or a group of buildings must be served by one cleaning system, better results can often be obtained by installing the dust separator at or near the center of the system of risers instead of close to the vacuum producer, as indicated in [Fig. 65]. When this is done, the pipe leading from the separator to the vacuum producer carries only clean air and can be made as large as desired and the friction loss reduced, resulting in a considerable reduction in the power required to operate the system.