Determination of Proper Size Pipe.
—Friction in the pipe lines tends to increase the vacuum to be maintained and therefore the power to be expended at the vacuum producer and should be kept as low as possible. The pipe sizes should be made as large as conditions will permit. The limit of size is fixed by the velocity in the pipe. When it is necessary to lift the dirt to any extent, the velocity should not be allowed to fall below 40 ft. per second at any time. When the pipe is a vertical drop, the velocity does not matter as gravitation will assist the air current in removing the dirt. When the line is horizontal a lower velocity than 40 ft. per second is permissible at times, provided that this minimum velocity is exceeded at frequent intervals to flush out any dirt that has lodged in the pipe during periods of low velocity.
If a Type A renovator is used with 1-in. hose and a vacuum of 10 in. of mercury maintained at the hose cock, the minimum air passing, with 100 ft. of hose in use, will be 29 cu. ft. of free air per minute, which is equivalent to 44 cu. ft. at 10 in. of vacuum. The entering velocity in the pipe should be calculated with air at this density. This will give a velocity of 50 ft. per second in a 1¹⁄₂-in. pipe, but only 30 ft. per second in a 2-in. pipe. Therefore, the 1¹⁄₂-in. pipe is the largest that should be used where lifts occur on a line serving but one Type A renovator with 1-in hose. When the renovator is tilted at a considerable angle or lifted from the carpet, as will frequently occur in cleaning operations, the quantity of air passing the renovator will be upwards of 42 cu. ft. of free air, equivalent to 62 cu. ft. at 10-in. vacuum. When this occurs the velocity in a 2-in. pipe will be 44 ft. per second, which will be ample to flush a horizontal line of piping.
If 1¹⁄₄-in. hose is used with a Type A renovator, the minimum quantity of air will be 29 cu. ft. and the vacuum entering the pipe will be 6 in. mercury, giving an equivalent volume of 37 cu. ft. This will produce a velocity of 42 ft. per second in a 1¹⁄₂-in. pipe, which is the largest that can be used where a lift occurs. However, when the renovator is lifted free of the carpet, the air quantity will be 62 cu. ft. of free air, equivalent to 80 cu. ft. at 6 in. of vacuum, and will produce a velocity of 39 ft. per second in a 2¹⁄₂-in. pipe. This would be just about sufficient to flush a horizontal line.
If 1¹⁄₂-in. hose were used the air quantity will be 29 cu. ft. and the vacuum entering the pipe 5 in. mercury, equivalent to 35 cu. ft. This will give a velocity in a 1¹⁄₂-in. pipe of 40 ft. per second. When the renovator is raised from the carpet, the air quantity will be upwards of 90 cu. ft. of free air, equivalent to 110 cu. ft. at the density of that entering the pipe, and will produce a velocity of 33 ft. per second in a 3-in. pipe. This is too low to thoroughly flush a horizontal pipe.
The figures given above are repeated from [Chapter VI] and show that the use of 1¹⁄₄-in. instead of 1-in. hose, permits the use of a larger-sized horizontal pipe line for serving one renovator, but that the use of 1¹⁄₂-in. hose, instead of 1¹⁄₄-in., will not permit of any enlargement in the pipe size. Since we have seen in [Chapter VI] that a 1¹⁄₄-in. hose gives the least expenditure of power when used with a Type A renovator, there will be no gain from a reduction in the pipe friction due to the adoption of this hose.
The dependence on the raising of the renovator from the floor to flush out a larger pipe line should not be carried beyond that to be obtained from a single renovator. That is, when the pipe must serve more than one renovator at the same time, the quantity of air that two or more renovators will pass, if they were raised from the floor at the same time, should not be used in determining the limiting velocity in the pipe, as such an occurrence is not likely to be obtained often enough to thoroughly flush the pipe. Furthermore, there will be times when this pipe will have to serve only one renovator and the pipe will not be adequately flushed. When the pipe is serving more than one renovator, the actual air passing the renovators should be used in determining the maximum size of pipe and it is advisable to use this maximum size in nearly all cases where the structural conditions will permit.
These sizes will then be:
TABLE 18.
Pipe Sizes Required, as Determined by Air Passing Renovators.
| Number of Renovators in Use. | Cu. Ft. per min. | Pipe Sizes, In. Diam. | |||
|---|---|---|---|---|---|
| With 1-in. Hose. | With 1¹⁄₄-in. Hose. | ||||
| 1 | 29 | 2 | 2 | ¹⁄₂ | |
| 2 | 58 | 2 | ¹⁄₂ | 2 | ¹⁄₂ |
| 3 | 87 | 3 | 3 | ||
| 4 | 116 | 3 | ¹⁄₂ | 3 | ¹⁄₂ |
| 5 | 145 | 3 | ¹⁄₂ | 3 | ¹⁄₂ |
| 6 | 174 | 4 | 4 | ||