From a branch supply line, a line runs out to each fixture (Fig. 8-2). Roughing-in is the process of getting all the pipes installed, capped, and pressure tested before actual fixtures are installed. The rough-in dimensions for
each plumbing fixture should be verified with the fixture manufacturer so that fixture supports can be built in accurately during the proper phase of construction.
It is a good idea to have a shutoff valve to control the flow of water at each vertical pipe (known as a riser), with branches for kitchens and baths and at the runouts to individual fixtures. Additional valves may be installed to isolate one or more fixtures from the water supply system for repair and maintenance. Compression-type globe valves are used for faucets, drain valves, and hose connections.
A dead-end upright branch of pipe located near a fixture is called an air chamber. When a faucet is shut off quickly, the water's movement in the supply pipe drops to zero almost instantly. Without the air chamber, the pressure in the pipe momentarily becomes very high, and produces a sound like banging the pipe with a hammer—appropriately called water hammer—that may damage the system. The air chamber absorbs the shock and prevents water hammer.
Vacuum breakers keep dirty water from flowing back into clean supply pipes. They also isolate water from dishwashers, clothes washers, and boilers from the water supply.
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