Residential Plumbing Venting
The simplest form of venting a trap or trapped fixtures is an individual vent for each trap.A single vent pipe is connected between the trap of a fixture and the branch connection to the drainage system.With a properly installed individual vent,only the drainage of the fixture served is flowing past the vent.
A common vent installed vertically may be used to protect two fixture traps when the drains connect at the same level on a vertical drain.A typical installations is two horizontal drains connecting together to a vertical drains to a double pattern fitting.The extension of the vertical pipe serves as a vent.The vent may connect at the interconnection of the fixture drains or downstream along the horizontal.A wet vent is a pipe that is wet because it also conveys drainage.
The wet venting concept is based on employing oversized piping to allow for the follow of air above the waste flow.The low probability of simultaneous fixture discharge and the low flow velocity that results from fixtures on the same floor level provide the nessary degree of realiability that there will always be adequate volume within the wet vent pipe to permit required airflow.Wet vents is permitted for both vertical and horizontal branch drains and includes what previously was referred to as stack venting.The vertical wet vent must extend from its connection to the dry vent to the lowest fixture drain connection.
Waste stack vent
A waste stack vent employs a waste stack as a vent for fixtures.The principles of use are based on some of the original research that was done in plumbing. The system has been identified by a variety of names, including vertical wet vent and muti-floor stack venting.
Because the the drainage stack serves as the vent,there are certain limitations placed on the design of the waste stack vent. The system prohibits the connection of water closets and urinals.Only waste can discharge to this vent.
The principal of circuit venting is that the flow of drainage never exceeds a half-full flow condition.The air for venting the fixtures circulates in the top half of the horizontal branch drainpipe.The flow velocity in the horizontal branch is slow and nonturbulent,therby preventing pressure differentials from affecting the connecting fixtures.The connection of the circuit vent must occur between the two most upstream fixture drains.The circuit vent pipe cannot receive the drainage of any soil or waste.The horizontal branch drain is limited to 8% slope.
Combination waste & Vent system
A combination drain and vent system is a means of extending the distance from a trap to its vent for an unimited distance because the vent and drain are literally one. The number of fixtures connecting to a combination drain and vent system is also unlimited,provided that the fixtures are floor drains,sinks,standpipes,drinking fountain or lavatories.The system is useful in areas that cannot accommodate vertical vent risers,such as where island sinks are installed or wher floor drains are located in large open areas.
Air Admittance Valves
Individual vents,branch vents,circuit vents and stack vents may all terminate with a connection to an air admittance valve rather than extend to the open air.Air enters the upper plumbing drainage system when negative pressures develop in the piping system. The device closes by gravity and seals the vent terminal when the internal pressure is equal to or greater than atmospheric pressure.Because an air admittance valve is capable of relieving only negative pressures, at least one stack vent or vent stack vent must extend outdoors.The vent to the open serves as the positive pressure relief for the drainage system.
A trap is a simple method used to keep sewer gases from emanating out of the drainage system.The water seal prevents the sewer gases and aerosal-borne bacteria from entering the living area.A trap is a simple U-shaped piping arrangement that offers minimal resistance to flow.This is the only type trap allowed.All other traps such as bell traps,drum traps,s-traps,and traps with moving parts are prohibited.