Drainage and Venting Systems Flashcards
6 cards from real 306A practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Drainage and Venting Systems flashcards as text
What is a 'crown vent'?
Answer: A vent connected at the crown (top bend) of a trap
A crown vent is connected at the crown (topmost point) of a trap. While this was an older practice, it is generally not recommended because water flowing past the vent connection can siphon out the trap seal.
What type of drainage system uses a single pipe for both waste removal and venting with no separate vent pipes?
Answer: Single-stack system (Philadelphia system)
The single-stack system (also called the Philadelphia or Sovent system) uses specially designed fittings and aerator-deaerator units to manage air flow within a single stack, eliminating the need for separate vent pipes.
What is the primary concern when sizing a horizontal storm drain?
Answer: The projected roof area drained and local rainfall intensity
Horizontal storm drains are sized based on the projected horizontal roof area being drained and the local design rainfall intensity, ensuring the pipe can convey peak storm water without surcharging.
What is the minimum slope for a horizontal storm drain 4 inches or larger?
Answer: 1 in 50 (2%)
Horizontal storm drains 4 inches and larger require a minimum slope of 1 in 50 (2%) to maintain adequate flow velocity for carrying storm water and preventing sediment accumulation.
What problem does 'back-pressure' cause in a drainage system?
Answer: Positive pressure that pushes trap seal water out into the fixture
Back-pressure occurs when positive pressure in the drain pushes against the underside of trap seals, potentially forcing sewer gases and contaminated water up through the trap and into the fixture. This commonly occurs at the base of tall stacks.
At the base of a soil stack, why is a stack offset of more than 45 degrees treated differently for venting purposes?
Answer: Because the offset acts like a horizontal drain where hydraulic jump and pressure fluctuations occur
An offset greater than 45 degrees behaves hydraulically like a horizontal pipe. At the transition point, the vertical flow hits the offset and creates a hydraulic jump and significant pressure fluctuations that require independent venting above and below the offset.