Master Plumber Exam Plumbing System Design & Sizing 3

Question 1

What is the primary purpose of an air gap in a plumbing system?

Accepted Answer

To prevent backflow by physical separation

Answer

An air gap is a physical separation between a water outlet and the flood-level rim of a receptor, providing the highest level of backflow protection.

Question 2

Per IPC, what is the minimum diameter of a building sewer serving 1–3 water closets?

Accepted Answer

4 inches

Answer

The IPC requires a building sewer to be at least 4 inches in diameter when water closets are connected.

Question 3

A pressure-reducing valve (PRV) should be installed when street pressure exceeds what threshold per IPC?

Accepted Answer

80 psi

Answer

Per IPC Section 604.8, a PRV is required when static pressure exceeds 80 psi to protect fixtures and appliances.

Question 4

Which pipe sizing approach accounts for velocity limits to prevent erosion and noise in copper water supply piping?

Accepted Answer

Velocity-based sizing limiting flow to 8 ft/s

Answer

Copper supply piping is typically limited to 8 feet per second to prevent erosion-corrosion, noise, and water hammer in the system.

Question 5

In a two-pipe venting system, each wet-vented drain serving fixtures must not exceed what maximum horizontal distance from the vent connection?

Accepted Answer

8 feet

Answer

IPC allows a wet-vented fixture drain to extend up to 8 feet horizontally from the wet vent connection before requiring individual venting.

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