Details Of Installation

Small service pipe connections to street mains are usually made by drilling and then tapping with a pipe thread the street main. A brass corporation cock, a, Fig. 91, to which is connected the service pipe, d, is then screwed into the street main. When the service pipe is made of brass or wrought iron, a short length of lead pipe laid wavy, should be inserted to provide a flexible connection that will not be affected by a subsequent settlement of either the service pipe or the street main.

In some waterworks systems where the pressure is low the street main is drilled and a corporation cock driven instead of being screwed into the main. While this form of corporation cock is extensively used, it is not wholly satisfactory even for low pressure systems, and owing to the great liability of their leaking they should never be used where the street mains are subjected to high pressure. Connections to the water mains are made by an employee of the municipality or water company that owns the system. This is done while the mains are under pressure and is accomplished without the loss of water from the mains. It is made possible by the use of a drilling and tapping machine designed for the purpose.

The largest tap permitted by most water companies is 3/4 inch diameter; hence, when larger sizes of service pipes are required, connections for them must be made to the street main either by inserting a special fitting or by means of a multiple service connection as shown in

Fig. 92. With a moderate sized street main, connections for service pipes over 2 1/2 inches diameter should be made by means of a special fitting; for all smaller sizes of service pipes and for all sizes of service pipes when the water main is extremely large, connections may be made by means of a multiple connection. In calculating the number of branch services for a multiple connection allowance should be made for the greater amount of friction in small pipes. This is no inconsiderable item as the following will show: At the same velocity of flow, doubling the diameter of a pipe increases its capacity four times; but the same head or pressure will produce different velocities in pipes of different sizes or lengths, and doubling the diameter of a pipe when the pressure remains constant, increases the capacity of the pipe about six times, the difference being usually stated to vary as the square root of the fifth power of the diameter. The number of small pipes required to equal the capacity of a large one can be found in the above table of equation of pipes.

Fig. 91

Fig. 92

Table XXXVI - Equation Of Pipes - Standard Steam And Gas Pipes