Figure 4-20. - Wet-barrel, or California, fire hydrant.
LEARNING OBJECTIVE: Understand disinfection chemicals, methods, and emergencies and their applications. Understand the application of pipe supports and insulation in water-supply systems.
Water mains, wells, filters, storage tanks, and other components of a water-supply system become contaminated during installation and repair. Flushing the system to remove dirt, waste, and surface water is the first step in disinfecting the water system, but it is not a sufficient safeguard. To ensure a safe water supply, you must thoroughly disinfect each unit of the system before it is placed in operation. The chemicals used in disinfecting a water-supply system are the same as those used in disinfecting water; for example, a hypochlorite solution or chlorine gas.
The chlorine dosage required to disinfect a unit depends upon the contact time and the amount of jute, untarred hemp, and organic chlorine-consuming material present. Under average conditions, the following minimum dosages are recommended:
|Unit||Minimum dosage (ppm)|
The volume of water in the unit to be disinfected must be computed before the chlorine dosage can be estimated. Use the formula for finding the volume of a tank (V = r2 h) and divide the volume by 231 to determine the number of gallons (231 cubic inches = 1 gallon). The volume of water in different sizes of pipe is listed below.
|Pipe diameter (inches)||Volume per foot of pipe (gallons)|
The following methods of applying disinfectants should be observed:
Liquid chlorine is applied by portable gas chlorinators. Chlorine cylinders should not be connected directly to mains because water may enter the cylinder and cause severe corrosion and hazardous leakage.Continue Reading