Waste Piping Networks

With the advent of readily available supplies of water inside the house, water began to be used to flush wastes down the drain. Water pipes from sinks, lavatories, tubs, showers, water closets (toilets), urinals, and floor drains form a network drained by gravity (Fig. 10-1). In order to preserve the gravity flow, large waste pipes must run

Figure 10-1 Waste piping network.

downhill, and normal atmospheric pressure must be maintained throughout the system at all times. Clean-outs are located to facilitate removal of solid wastes from clogged pipes.

Cast iron is used for waste plumbing in both small and large buildings. Cast iron was invented in Germany in 1562 and was first used in the United States in 1813. It is durable and corrosion resistant. Cast iron is hard to cut, and was formerly joined at its hub joints using molten lead. Today, cast-iron pipes use hubless or bell-and-spigot joints and fittings or a neoprene (flexible plastic) sleeve.

Plastic pipes made of ABS or PVC plastic are lightweight and can be assembled in advance. Copper pipes have been used since ancient times. Some building codes also allow galvanized wrought iron or steel pipes.

Engineers size waste plumbing lines according to their location in the system and the total number and types of fixtures they serve. Waste piping is laid out as direct and straight as possible to prevent deposit of solids and clogging. Bends are minimized in number and angled gently, without right angles. Horizontal drains should have a 1 : 100 slope (8 in. per foot) for pipes up to 76 mm (3 in.) in diameter, and a 1:50 slope (4 in. per foot) for pipes larger than 76 mm. These large, sloping drainpipes can gradually drop from a floor through the ceiling below and become a problem for the interior designer.

Cleanouts are distributed throughout the sanitary system between fixtures and the outside sewer connection. They are located a maximum of 15 meters (50 ft) apart in branch lines and building drains up to 10 cm (4 in.). On larger lines, they are located a maximum of 30.5 meters (100 ft) apart. Cleanouts are also required at the base of each stack, at every change of direction greater than 45 degrees, and at the point where the building drain leaves the building. Wherever a cleanout is located, there must be access for maintenance and room to work, which may create problems for the unwary interior designer.

Fixture drains extend from the trap of a plumbing fixture to the junction with the waste or soil stack. Branch drains connect one or more fixtures to soil or waste stacks. A soil stack is the waste pipe that runs from toilets and urinals to the building drain or building sewer. A waste stack is a waste pipe that carries wastes from plumbing fixtures other than toilets and urinals. It is important to admit fresh air into the waste plumbing system, to keep the atmospheric pressure normal and avoid vacuums that could suck wastes back up into fixtures. A fresh-air inlet connects to the building drain and admits fresh air into the drainage system of the building. The building sewer connects the building drain to the public sewer or to a private treatment facility such as a septic tank.

Floor drains are located in areas where floors need to be washed down after food preparation and cooking. They allow floors to be washed or wiped up easily in shower areas, behind bars, and in other places where water may spill.

Interceptors, also known as traps, are intended to block undesirable materials before they get into the waste plumbing. Among the 25 types of interceptors are ones designed to catch hair, grease, plaster, lubricating oil, glass grindings, and industrial materials. Grease traps are the most common. Grease rises to the top of the trap, where it is caught in baffles, preventing it from congealing in piping and slowing down the digestion of sewage. Grease traps are often required by code in restaurant kitchens and other locations.

Sewage ejector pumps are used where fixtures are below the level of the sewer. Drainage from the below-grade fixture flows by gravity into a sump pit or other receptacle and is lifted up into the sewer by the pump. It is best to avoid locating fixtures below sewer level where possible, because if the power fails, the equipment shuts down and the sanitary drains don't work. Sewage ejector pumps should be used only as a last resort.

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