Drainage, Waste & VentQuestion 7 of 120
A 2 in trap arm serves a floor-mounted fixture. The trap weir is at elevation 0. What is the greatest amount the trap arm may fall before it reaches the vent connection?
a.1/2 in
b.1 in
c.1-1/2 in
d.2 in
Explanation
The trap arm may not fall more than one pipe diameter between the trap weir and the vent opening, so a 2 in arm may drop a maximum of 2 in. Any greater fall lets the crown of the arm flood and the fixture becomes self-siphoning. The smaller values correspond to diameters of other pipe sizes, not the 2 in arm in question.
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