306A Drainage and Venting Systems 4

Question 1

What causes self-siphonage in a plumbing trap?

Accepted Answer

The momentum of water leaving the fixture creates a vacuum that pulls the trap seal out

Answer

Self-siphonage occurs when the slug of water leaving the fixture creates negative pressure behind it in the trap arm, pulling the trap seal water out through siphonic action. Proper venting prevents this by admitting air behind the water slug.

Question 2

What is 'induced siphonage' in a drainage system?

Accepted Answer

Trap seal loss caused by the discharge of another fixture on the same branch

Answer

Induced siphonage occurs when a nearby fixture discharges and creates negative pressure in the shared branch drain, pulling the trap seal from an adjacent, non-discharging fixture. Proper branch venting prevents this.

Question 3

What is the fixture unit rating for a shower stall in a residential building?

Accepted Answer

2 fixture units

Answer

A residential shower stall is rated at 2 fixture units, reflecting its drainage flow rate and load on the drainage and venting system.

Question 4

What is the minimum pipe size for a building storm drain?

Accepted Answer

4 inch

Answer

The minimum building storm drain size is 4 inches to handle the volume of rainwater collected from roof areas, ensuring adequate capacity during heavy rainfall.

Question 5

What determines the size of a roof drain leader (rain water leader)?

Accepted Answer

The area of roof being drained and the local rainfall intensity

Answer

Roof drain leaders are sized based on the horizontal roof area being drained and the local rainfall intensity (typically in mm/hour for a 5-minute duration, 10-year return period), ensuring the pipe can handle peak storm flows.

Red Seal Plumber 306A Practice Test

Red Seal Plumber 306A Practice Test

306A Drainage and Venting Systems 4