Q.
The Single Stack System is the simplification of the one pipe system. Explain using diagrams the construction of the single stack system and give its advantages as compared to the one pipe system.
(25 marks, 2015 Q4)
A.
[The key difference from one pipe system is the vents of one pipe system is stacked on each other to single pipe at the trunk. This means the vent for individual branch is omitted and instead rely on the trunk which opens out as the Main Vent.
When the sewerage drains to the outlet beneath, the vent on top - stacked, would allow the release of the pressure. Imagine if it is closed, the downward pressure of sewerage would create vacuum, and it would not drain smoothly. For tall buildings with many floors, when the rush of sewerage is concentrated at the same trunk, it might be impossible to drain out instantly at one single time.
For example, during the half-time recess of a World Cup football match, all the flushing of toilet would flood the main trunk. This will overload the capacity of the trunk. Thus, single stack system with modification of more vents is needed for tall buildings.
Otherwise, single stack system is more cost saving (with less branch vents) and serves as good as the one pipe system.
Compare with the diagram below the one pipe system to two pipes system and the single stack system.]
Ref:
[x] Own account.
Slides by Rabia Sultana, available at
https://www.slideshare.net/mobile/RabiaS1/drainage-system-one-pipe