The basic principle of this system is to collect and convey the waste water through the drain pipes by gravity and then their subsequent emission into the public sewer or domestic septic tank.
Aims of a sanitation/drainage system
- To maintain healthy conditions in the building
- To dispose of waste water as early and quickly as possible
- To avoid entry of foul gases from sewer or septic tank
- To systematically collect and dispose wastes in a fluid form
Design and sizing of sewage collection systems considers population served, commercial and industrial flows, flow peaking characteristics and wet weather flows. Combined sewer systems are designed to transport both storm water runoff and sewage in the same pipe. Besides the projected sewage flow, the size and characteristics of the watershed are the overriding design considerations for combined sewers. Often, combined sewers cannot handle the volume of runoff, resulting in combined sewer overflows and causing water pollution problems in nearby water bodies.
Separate sanitary sewer systems are designed to transport sewage alone. In communities served by separate sanitary sewers, another pipe system is constructed to convey storm water runoff directly to surface waters. Most municipal sewer systems constructed today are separate sewer systems.
Although separate sewer systems are intended to transport only sewage, all sewer systems have some degree of inflow and infiltration of surface water and groundwater, which can lead to sanitary sewer overflows. Inflow and infiltration is highly affected by antecedent moisture conditions, which also represents an important design consideration in these system.
A sewer bed is a piece of land typically used by a municipality for the dumping of raw sewage. Usually raw sewage was brought by truck or drawn by horses to be dumped, but the practice stopped back in the 1940s.
Drain/waste water system fittings
Because they operate at low pressure and rely on gravity to move fluids (and often entrained solids), drain-waste-vent systems use fittings designed to be as smooth as possible on their interior surfaces. The fittings may be “belled” or expanded slightly in diameter, or otherwise shaped to accommodate insertion of pipe or tubing, without forming a sharp interior ridge that might catch debris or accumulate buildup of material and cause clogging. The absence of interior snags also makes it much easier to “snake out” or “rod out” a clogged pipe using long flexible tools made for this purpose.
Underground piping systems for landscaping drainage, or disposal of storm water or groundwater, similarly use gravity flow at low pressure, often with entrained solids. Piping fittings used for these systems bear a strong resemblance to DWV fittings, though often at a larger scale. When high peak flow volumes are involved, the design and construction of these systems are closely inter-related to sewer design.
Fittings for central vacuum systems are very similar to DWV fittings, though usually of thinner and lighter construction, since the weight of the materials conveyed through the system is much less. Vacuum system designs share with DWV designs a concern about eliminating internal ridges, burrs, sharp turns, or other obstructions to smooth flow that might cause build-up of material into pipe blockages.
Sweep Elbow – DWV elbows are usually long radius or sweep types, to reduce flow resistance and solids deposition when the direction of flow is changed. A well-designed system will often employ multiple 45° elbows in preference over 90° elbows (even sweep elbows), to reduce flow disruption as much as possible.
Central vacuum system inlet fittings are intentionally designed with a tighter radius of curvature than any other bends in the system. This is done to ensure that if any vacuumed debris becomes stuck, it will jam right at the inlet, where it is easiest to discover and to remove.
Closet Flange – The closet flange is the drain pipe flange to which a water closet (toilet) is attached. It is a specialized type of flange connection designed to sit flush with the floor, allowing a standard toilet to be installed above it.
Clean-outs – Clean-outs are fittings with removable elements that allow access to drains without requiring removal of plumbing fixtures. They are used for allowing an auger or plumber’s snake to clean out a plugged drain. Clean-outs should be placed in accessible locations at regular intervals throughout a drainage system, often including outside the building, because clean-out augers have limited length. The minimum requirement is typically at the end of each branch in piping, just ahead of each water closet, at the base of each vertical stack, and both inside and outside the building in the building main drain/sewer. Clean-outs normally have screw-on caps or screw-in plugs.
Trap Primers – Trap primers regularly inject water into traps so that “water seals” are maintained, as necessary to keep sewer gases out of buildings. The trap primer must be installed in a readily available place for easy access for adjustments, replacement, and repair. Strictly speaking, a trap primer is a specialized valve, and it is usually connected to a clean water supply, in addition to a DWV system. Because of this dual connection, the design usually must be certified to resist accidental backflow of contaminated water.
Combo-Tee – A combination tee (combo tee) is a tee with a gradually curving center connecting joint. It is used in drain systems to provide a smooth, gradually curving path to reduce the likelihood of clogs, and to ease pushing a plumber’s snake through a drain system. The “combo” is a combination of a wye and a 1/8 bend or 45° elbow.
Sanitary Tee – A sanitary tee is a tee with a curved center section. In drainage systems it is primarily used to connect horizontal drains ( including fixture trap arms) to vertical drains. (It is against all major codes to use a sanitary tee to connect a vertical drain to a horizontal drain.) The center connection is generally connected to the pipe which leads to a trap (the trap arm).
Double sanitary tee (sanitary cross) – Similar to a cross. This fitting differs from a standard cross in that two of the ports have curved inlets. The fitting has been used in the past for connecting the drains of back-to-back fixtures (such as back-to-back bathroom sinks). Some current codes (including the 2006 UPC) prohibit the use of this fitting for that purpose, instead requiring a special “double fixture fitting” (double combination wye).
Wye fitting – A fitting with three openings, a wye is used to create branch lines. It is a type of waste fitting tee which has the side inlet pipe entering at a 45° angle, or an angle other than 90 degrees. A standard waye is a “Y” shaped fitting which allows one pipe to be joined to another at a 45 degree angle.
Wyes are similar to tees except that the branch line is angled to reduce friction and turbulence that could hamper the flow. The connection is typically at a 45-degree angle rather than a 90-degree angle. If a branch turns out further at the end to be perpendicular to the through line, the fitting becomes a “tee wye” (TY). PVDF Corrosive Waste Piping Systems utilize wye fittings that feature a smooth inside diameter without any irregularities, for uninterrupted flow path. These fittings should be able to withstand acids, bases, and solvents. Flame-retardant systems withstand intermittent corrosive fluids up to high temperatures. Polypropylene and PVDF Double Wyes and Double Reducing Wyes come in various sizes and are largely used for this purpose.
A waye branch allows splitting a branch line equally in two directions. The opening sizes can vary for different situations, for instance in situation where a large main line needs to be split into two smaller branches.
Low-priced wyes are often spot-welded together, whereas industrial wyes have a continuous weld at each seam. In long-distance pipeline applications, a true Wye fitting is also engineered for closed system instrumentation pigging configurations or wherever a smooth pipe branch is required.
Double-tapped bushing – A double-tapped bushing is a fitting that has opposing threads on the inside diameter of the bushing.
