306A Drainage and Venting Systems 3

Question 1

What is a 'combination waste and vent' system?

Accepted Answer

A system where oversized horizontal waste pipes serve as both drain and vent for floor drains and similar fixtures

Answer

A combination waste and vent system uses oversized horizontal waste pipes that are large enough to flow only partially full, leaving the upper portion of the pipe as an air passage for venting. This is typically limited to floor drains and similar fixtures.

Question 2

When connecting two drainage pipes at a junction, why is a wye and 45-degree bend preferred over a tee?

Accepted Answer

It provides a smoother flow transition and reduces turbulence

Answer

A wye and 45-degree bend provides a gradual directional change that guides waste flow smoothly into the main pipe, reducing turbulence, scouring, and the potential for blockages compared to a tee's abrupt 90-degree entry.

Question 3

What is the maximum offset angle permitted in a soil or waste stack without special venting?

Accepted Answer

45 degrees

Answer

A stack offset up to 45 degrees from vertical does not require special venting because the flow characteristics remain similar to vertical flow. Offsets greater than 45 degrees are treated as horizontal pipes and require separate venting.

Question 4

Why must a vent pipe always rise above the fixture flood level rim before connecting horizontally to the vent stack?

Accepted Answer

To prevent waste water from flowing into the vent during a fixture backup

Answer

The vent must rise above the fixture flood level rim before running horizontally to ensure that waste water cannot enter the vent pipe if the fixture backs up or overflows.

Question 5

What is the minimum grade required for a vent pipe that runs horizontally?

Accepted Answer

1 in 100 back toward the drainage pipe it serves

Answer

Horizontal vent pipes must slope at a minimum of 1 in 100 back toward the drainage pipe to allow any condensation to drain back into the waste system rather than accumulating and blocking the vent.

Red Seal Plumber 306A Practice Test

Red Seal Plumber 306A Practice Test

306A Drainage and Venting Systems 3