These sizes will be dependent on the location in which it is necessary to install the vacuum producer. In the case of the building ([Fig. 61]) the most desirable location for the vacuum producer will be in the exact center of the building.
With the vacuum producer centrally located the longest run from any riser will be 55 ft. To this we must add:
5 ft. for each long-turn elbow.
10 ft. for each short-turn elbow.
10 ft. for entrance to each long sweep Y branch.
20 ft. for entrance to a tee branch, except at sweeper inlets on risers, where 10 ft. is ample.
In calculating the riser friction for risers under 150 ft. in length the whole capacity of the riser can be assumed as being connected to a point midway of its length.
In the eight-story building ([Fig. 61]) the length of the riser from basement ceiling to eighth floor will be 100 ft. and the length to be figured, 50 ft. The equivalent length of pipe line for any of the risers, with the vacuum producer centrally located, will be:
| From entrance tee into riser | 10 ft. |
| Length of riser, one-half total length | 50 ft. |
| Turn at base of riser | 10 ft. |
| Run in basement | 55 ft. |
| Y branch or elbow | 10 ft. |
| Elbow at separator | 5 ft. |
| Equivalent length | 140 ft. |
Each riser is to serve two sweepers and must pass 140 cu. ft. of free air per minute. This will give a friction loss in a 2¹⁄₂-in. pipe of 2 in. mercury, if 10 in. mercury be maintained at the hose cock and 1-in. hose used; and 1.5 in. mercury if 6 in. mercury be maintained at the hose cock and 1¹⁄₄-in. hose used. Either of these figures are within the limits set for the maximum friction loss and 2¹⁄₂-in. pipe will be the proper size for the risers and their branches in the basement.