Tighten the chain mounting bolts until a solid, watertight connection is formed between the main and the base of the machine. Check the depth adjustment on the boring bar, and insert the proper size drill and tap into the holder. Assemble the machine by inserting the boring bar through the cylinder and tightening the cap. Start drilling the hole by applying pressure at the feed yoke while operating the ratchet handle. After the drill penetrates the main, the boring bar turns easily until the tap starts cutting threads. When the tap starts threading the hole, back off of the feed yoke to prevent the threads in the main from stripping. Continue to turn the boring bar until the depth adjustment hits the stop. You have hit the stop when the ratchet handle tightens and it can no longer be tightened without undue force. To remove the tap from the hole, reverse the ratchet and back the boring bar out by turning it counterclockwise. When the boring bar is raised high enough to clear the bottom of the cylinder, close the flop valve. Check to see that the bypass valve is closed. This prevents water from entering the cylinder. The water under pressure from the main is now trapped in the base of the machine, and the boring bar can be removed by unscrewing the machine cap. Remove the drill and tap tool and install a corporation stop of the proper size in the end of the boring bar. Be sure the handle of the corporation stop is in the CLOSED position. Reinstall the boring bar in the cylinder and tighten the cap. Open the bypass valve to allow the water-main pressure into the cylinder, so the flop valve can be opened again. The corporation stop can now be screwed into the main by turning the boring bar. Since the corporation stop was closed before being installed, the only noticeable water leak from the operation is from the water trapped in the cylinder of the machine. Release the water pressure from the cylinder by opening the bypass valve and removing the boring bar. Disengage the chain from the main and remove the machine. Check for leakage around the corporation stop. If the corporation stop leaks, tighten it with an adjustable jaw wrench.

DISTRIBUTION SYSTEM ELEMENTS

The elements of a distribution system include distribution mains, arterial mains, storage reservoirs, and system accessories (including booster stations, valves, hydrants, main-line meters, service connections, and backflow preventers).

Distribution mains are the pipelines that make up the distribution system. Their function is to carry water from the water source or treatment works to users.

Arterial mains are large-size distribution mains. They are interconnected with smaller distribution mains to form a complete gridiron system.

Storage reservoirs are structured to store water. They may serve to equalize the supply or pressure in the distribution system.

System accessories include the following:

Booster stations that pump water from storage or a relatively low-pressure main to the distribution system, or it may serve a portion of the system that is at a higher elevation.

Valves that serve to control the flow of water in the distribution system by isolating areas for repair or by regulating system flow or pressure.

Hydrants that are designed to allow water from the distribution system to be used for fire-fighting purposes.

Main-line meters that serve to record the flow of water in a part of the distribution system.

Service connections that connect either an individual building or other plumbing system to the distribution-system mains.

Backflow preventers that protect the water source from contamination.

SYSTEM LAYOUT AND SIZE

When distribution systems are carefully planned, the pipes are usually laid out in a grid or belt system. A network of large pipes divides the community or base into areas of several blocks each (fig. 4-36). The streets within each area are served by smaller pipes connected to the larger ones. When possible, the network is planned so the whole pipe system consists of loops, and no pipes come to a dead end. In this way, water can flow to any point in the system from two or more directions; hence, the water supply need not be cut off for maintenance work or a break in a pipe.

Older water systems frequently were expanded without planning and developed into a treelike system. This consists of a single main that decreases in size, as it leaves the source and progresses through the area originally served. Smaller pipelines branch off the main and divide again, much like the trunk and branches of a tree. A treelike system is not desirable because the size of the old main limits the expansion of the system needed to meet increasing demands. Also, there are many dead ends in the system where