ETC ETC Mechanical Systems & Equipment 2 — Questions and Answers
Question 1: What is the purpose of an expansion joint in a piping system?
- To increase pipe diameter at equipment connections
- To allow for thermal expansion and contraction without stressing pipe or equipment (Correct answer)
- To connect pipes of dissimilar materials
- To provide access for pipeline inspection
Correct answer: To allow for thermal expansion and contraction without stressing pipe or equipment
Expansion joints absorb dimensional changes caused by temperature variations, preventing thermal stress and potential failure in piping systems.
Question 2: What does NPSH represent for a centrifugal pump?
- The maximum pressure a pump can develop at shutoff
- The pressure available at the pump inlet above vapor pressure, preventing cavitation (Correct answer)
- The net pump efficiency after mechanical losses
- The minimum pipe diameter required on the pump suction side
Correct answer: The pressure available at the pump inlet above vapor pressure, preventing cavitation
NPSH is the difference between the absolute pressure at the pump suction and the vapor pressure of the liquid, determining whether cavitation will occur.
Question 3: What is the purpose of a pressure reducing valve in a water distribution system?
- To increase pressure for high-rise buildings
- To reduce upstream pressure to a lower regulated downstream pressure (Correct answer)
- To prevent backflow from the building into the main
- To measure system pressure at the service connection
Correct answer: To reduce upstream pressure to a lower regulated downstream pressure
A PRV reduces high upstream water pressure to a safe, regulated level suitable for building fixtures and piping systems.
Question 4: What is the refrigeration cycle's primary purpose in an air conditioning system?
- To generate electrical power for the building
- To transfer heat from the indoor space to the outdoor environment using a refrigerant (Correct answer)
- To dehumidify air by heating it above the dew point
- To filter outdoor air before distributing it through the building
Correct answer: To transfer heat from the indoor space to the outdoor environment using a refrigerant
The refrigeration cycle uses a refrigerant to absorb heat inside the building and reject it outside, cooling the interior space.
Question 5: What does brake horsepower measure for a pump or motor?
- The rated nameplate horsepower from the manufacturer
- The actual power delivered to the pump shaft, accounting for mechanical losses (Correct answer)
- The electrical power drawn by the motor from the supply
- The maximum power before the circuit breaker trips
Correct answer: The actual power delivered to the pump shaft, accounting for mechanical losses
Brake horsepower is the actual mechanical power delivered at the shaft, which is less than motor nameplate power due to mechanical inefficiencies.
Question 6: What is the purpose of a variable air volume (VAV) box in an HVAC system?
- To increase supply air pressure for high floors
- To modulate airflow to individual zones based on thermostat demand (Correct answer)
- To filter supply air for individual rooms
- To recover heat from exhaust air in each zone
Correct answer: To modulate airflow to individual zones based on thermostat demand
A VAV box regulates the volume of conditioned air supplied to a zone by varying the damper position in response to the zone thermostat setpoint.
ETC ETC Mechanical Systems & Equipment 2
What is the purpose of an expansion joint in a piping system?