CET Hydraulic Elevator Systems 2 — Questions and Answers
Question 1: What is the primary purpose of a hydraulic elevator's lowering valve?
- To increase pump pressure during descent
- To control the rate of fluid return to the tank during down travel (Correct answer)
- To prevent the car from moving upward when unloaded
- To regulate motor speed during descent
Correct answer: To control the rate of fluid return to the tank during down travel
The lowering valve meters fluid flow back to the reservoir, controlling descent speed.
Question 2: A hydraulic elevator experiences 'rough ride' during up travel only. The MOST likely cause is:
- Contaminated hydraulic fluid
- Air trapped in the hydraulic cylinder
- A worn pump coupling (Correct answer)
- Low oil level in the reservoir
Correct answer: A worn pump coupling
A worn or damaged pump coupling causes vibration and rough ride specifically during the up direction when the pump is driving the load.
Question 3: What does the term 'telescoping cylinder' refer to in hydraulic elevator design?
- A cylinder that rotates to extend the plunger
- A multi-stage cylinder where inner sections extend sequentially for greater travel (Correct answer)
- A cylinder mounted at an angle to save pit space
- A cylinder with a variable bore diameter
Correct answer: A multi-stage cylinder where inner sections extend sequentially for greater travel
A telescoping cylinder uses nested stages that extend sequentially, allowing longer travel than a single-stage cylinder of the same retracted length.
Question 4: According to ASME A17.1, the maximum pressure above which a hydraulic elevator relief valve must open is:
- 110% of working pressure
- 125% of working pressure (Correct answer)
- 150% of working pressure
- 200% of working pressure
Correct answer: 125% of working pressure
ASME A17.1 requires the relief valve to open at no more than 125% of the system working pressure to protect against overpressure.
Question 5: In a roped hydraulic elevator, what is the mechanical advantage provided by a 2:1 roping ratio?
- The cylinder travels twice as fast as the car
- The car travels twice as far as the cylinder stroke (Correct answer)
- The cylinder pressure is doubled compared to direct-acting
- The pump flow rate is halved
Correct answer: The car travels twice as far as the cylinder stroke
A 2:1 roping ratio means the car travels twice the distance of the cylinder stroke, allowing shorter cylinders for taller rises.
Question 6: What type of hydraulic fluid is recommended for environmentally sensitive installations?
- Petroleum-based ISO VG 46 fluid
- Biodegradable vegetable-based or synthetic ester fluid (Correct answer)
- Water-glycol hydraulic fluid
- Phosphate ester fire-resistant fluid
Correct answer: Biodegradable vegetable-based or synthetic ester fluid
Biodegradable vegetable-based or synthetic ester fluids are used in environmentally sensitive areas because they break down naturally if spilled.
Question 7: A hydraulic elevator pit has an accumulation of hydraulic oil. The FIRST corrective action should be:
- Absorb the oil and continue operation
- Identify and repair the source of the leak before resuming service (Correct answer)
- Add oil to the reservoir to compensate for the loss
- Increase system pressure to push the oil back
Correct answer: Identify and repair the source of the leak before resuming service
The source of the leak must be found and repaired before returning the elevator to service to prevent continued fluid loss and potential fire hazard.
CET Hydraulic Elevator Systems 2
What is the primary purpose of a hydraulic elevator's lowering valve?