Building Drainage Systems Flashcards
Single stack system
Sanitary fitments are individually connected to the vertical drainage.
Any self siphonage does not affect the trap seal of the others.
Fitments close to the vertical drainage stack
Only for low-rise buildings
Two-pipe system
Separate soil and waste.
Each stack is paired with a vent stack
System avoids foul air going into the waste fitment of the dried trap
Expensive system, difficult to maintain and requires large space installation (4 vertical stacks for flowing air and water for soil and waste water)
One pipe system
All soil and waste water flows into the single soil stack.
A vent stack is provided.
More economical and requires less space.
Loss of trap seal should be prevented.
Air pressure inside the drain pipe
Excessive negative pressure remove water seals, excessive positive pressure may blow the foul air
When is expected the air pressure drop?
Due to the pipe friction between air and the vertical stack
When annular discharged is induced downward air movement?
When water discharges from the branches to the sack and also air entrainment from the top of the drainage sack
When is the effective cross-section area of the stack reduced?
When air passes through the branch connections
When is the air passing through to downstream prevented?
When the annular flow of water forms a water curtain at the base of the vertical sack
When does the air blows through the water curtain and flows to the downstream of the vertical sack?
When the air pressure reaches the threshold
When are cross vents provided?
Every 3-4 floors
