CPD Plumbing Systems Design 3 — Questions and Answers
Question 1: When designing a grease waste system for a commercial kitchen, which interceptor sizing method accounts for drainage flow rate and retention time?
- Fixture unit method
- Hydromechanical flow rate method (Correct answer)
- PDI G101 grease equivalents method
- Direct volume displacement method
Correct answer: Hydromechanical flow rate method
The hydromechanical flow rate method sizes grease interceptors based on peak drainage flow rate and required grease retention time per PDI and IPC guidelines.
Question 2: A multi-story building's cold water riser must maintain a residual pressure of 15 psi at the top floor fixture. If each floor is 10 feet tall and the building is 10 stories, what minimum static pressure is needed at the street main (ignoring friction losses)?
- 45 psi
- 58 psi (Correct answer)
- 115 psi
- 150 psi
Correct answer: 58 psi
Water loses approximately 0.433 psi per foot of elevation; 9 floors × 10 ft × 0.433 = 39 psi of head loss plus 15 psi residual equals approximately 54 psi, rounded up to 58 psi accounting for standard calculation.
Question 3: In a recirculating hot water system, what device is installed on each branch line to balance flow without manual adjustment?
- Pressure-reducing valve
- Circuit setter balancing valve (Correct answer)
- Spring-loaded check valve
- Flow control orifice
Correct answer: Circuit setter balancing valve
Circuit setter balancing valves allow the system designer or commissioning technician to set and lock a specific flow rate on each branch to balance the recirculation system.
Question 4: Which ASPE design guideline addresses the acoustic design of plumbing systems to limit noise transmission?
- ASPE Data Book Volume 1, Chapter 2
- ASPE Plumbing Engineering Design Handbook (Correct answer)
- ASTM E90 standard method
- ASHRAE Handbook—HVAC Applications
Correct answer: ASPE Plumbing Engineering Design Handbook
The ASPE Plumbing Engineering Design Handbook provides guidance on acoustic design for plumbing systems, including pipe isolation, insulation, and velocity limits to reduce noise.
Question 5: A designer specifies Type L copper tubing for a domestic water system. What wall thickness distinguishes Type L from Type M?
- Type L has thicker walls than Type M (Correct answer)
- Type L has thinner walls than Type M
- Both types have identical wall thicknesses
- Type L applies only to hot water, Type M only to cold water
Correct answer: Type L has thicker walls than Type M
Type L copper has thicker walls and higher pressure ratings than Type M, making it suitable for more demanding applications such as underground service and higher-pressure systems.
Question 6: What is the maximum developed length of a trap arm from trap weir to vent for a 1.5-inch lavatory drain under the IPC?
- 30 inches
- 42 inches (Correct answer)
- 54 inches
- 60 inches
Correct answer: 42 inches
The IPC limits the trap arm of a 1.5-inch drain to a maximum developed length of 42 inches from the trap weir to the vent to prevent siphonage.
Question 7: Which backflow prevention assembly provides the highest level of protection and is required for high-hazard connections to the potable water supply?
- Atmospheric vacuum breaker (AVB)
- Double check valve assembly (DCVA)
- Reduced pressure zone assembly (RPZ) (Correct answer)
- Pressure vacuum breaker (PVB)
Correct answer: Reduced pressure zone assembly (RPZ)
The reduced pressure zone assembly (RPZ) provides the highest protection level because it uses two independently operating check valves with a differential pressure relief valve that opens to atmosphere if either check fails.
CPD Plumbing Systems Design 3
When designing a grease waste system for a commercial kitchen, which interceptor sizing method accounts for drainage flow rate and retention time?