CET Hydraulic Elevator Systems 3 — Questions and Answers
Question 1: What is the function of a hydraulic elevator's anti-creep feature?
- Prevents the car from leveling at the floor
- Automatically corrects slow unintended car movement due to internal valve leakage (Correct answer)
- Limits maximum car speed during up travel
- Prevents the pump from starting under load
Correct answer: Automatically corrects slow unintended car movement due to internal valve leakage
The anti-creep circuit detects slow unintended movement and runs the pump briefly to restore the car to floor level.
Question 2: Which component in a hydraulic power unit prevents the pump from operating against a closed system when the car reaches the top landing?
- The relief valve
- The check valve
- The up-limit switch that de-energizes the pump motor (Correct answer)
- The lowering valve solenoid
Correct answer: The up-limit switch that de-energizes the pump motor
The up-limit switch de-energizes the pump motor when the car reaches the top terminal, preventing the relief valve from having to handle continuous full-pressure bypass.
Question 3: Hydraulic oil viscosity MOST directly affects elevator performance by:
- Changing the electrical resistance of solenoid valves
- Altering flow rates through valves, which impacts leveling and ride quality (Correct answer)
- Increasing the mechanical strength of the cylinder
- Reducing motor current draw at low temperatures
Correct answer: Altering flow rates through valves, which impacts leveling and ride quality
Viscosity determines how easily fluid flows through valves and orifices, directly affecting leveling accuracy, speed, and ride quality.
Question 4: When performing a pressure test on a hydraulic elevator, the system pressure is typically held at what level above working pressure?
- 10% above working pressure for 5 minutes
- 50% above working pressure for 24 hours (Correct answer)
- 150% of working pressure for 5 minutes
- Working pressure only, for 1 hour
Correct answer: 50% above working pressure for 24 hours
ASME A17.1 requires a pressure test at 150% of working pressure, held for a specified period to verify cylinder and piping integrity.
Question 5: What is the purpose of a silencer or muffler installed on a hydraulic elevator pump unit?
- To reduce heat generated by the hydraulic fluid
- To dampen pressure pulsations and reduce noise from the pump (Correct answer)
- To filter particulates from the return oil
- To prevent cavitation in the pump inlet
Correct answer: To dampen pressure pulsations and reduce noise from the pump
Hydraulic pump silencers are installed in the pressure line to absorb pulsations that cause noise and vibration in the piping and car.
Question 6: A submersible hydraulic power unit differs from a surface-mounted unit in that:
- The motor is located in the machine room above the elevator
- The entire pump-motor assembly is submerged inside the oil reservoir (Correct answer)
- It uses a different type of hydraulic fluid
- It requires a larger pit depth
Correct answer: The entire pump-motor assembly is submerged inside the oil reservoir
Submersible units place the motor and pump inside the fluid tank, reducing noise and eliminating the need for a separate machine room.
Question 7: In a hydraulic elevator system, what is the role of the check valve located between the pump and the cylinder?
- It allows flow in both directions at controlled rates
- It prevents fluid from returning to the pump when the pump is off, holding the car in position (Correct answer)
- It regulates maximum system pressure
- It filters contaminants from the pressure line
Correct answer: It prevents fluid from returning to the pump when the pump is off, holding the car in position
The check valve allows flow only from pump to cylinder, preventing backflow that would allow the car to descend when the pump stops.
CET Hydraulic Elevator Systems 3
What is the function of a hydraulic elevator's anti-creep feature?