EVT EVT Hydraulic Systems & Aerial Apparatus 1 — Questions and Answers
Question 1: What is the primary function of a hydraulic relief valve in an aerial apparatus system?
- To increase pump pressure
- To prevent system overpressure by diverting excess fluid (Correct answer)
- To filter hydraulic fluid contaminants
- To measure fluid viscosity
Correct answer: To prevent system overpressure by diverting excess fluid
A hydraulic relief valve protects the system by diverting excess fluid back to the reservoir when pressure exceeds a set limit.
Question 2: Which type of hydraulic pump is most commonly used in aerial ladder apparatus due to its ability to deliver constant flow?
- Gear pump
- Vane pump
- Piston pump (Correct answer)
- Centrifugal pump
Correct answer: Piston pump
Piston pumps are preferred in aerial apparatus because they provide high-pressure, constant-flow output needed for reliable aerial operations.
Question 3: According to NFPA 1901, aerial devices must be tested at what percentage above their rated working load?
- 100%
- 125%
- 150% (Correct answer)
- 200%
Correct answer: 150%
NFPA 1901 requires aerial devices to be proof-tested at 150% of their rated working load during annual certification.
Question 4: What condition is indicated when a hydraulic cylinder drifts under load with no control input?
- Normal thermal expansion
- Internal cylinder seal leakage (Correct answer)
- Low hydraulic fluid temperature
- Excessive pump speed
Correct answer: Internal cylinder seal leakage
Cylinder drift under load indicates internal seal leakage, allowing fluid to bypass the piston and causing unintended movement.
Question 5: What is the purpose of a hydraulic accumulator on an aerial apparatus?
- Filter hydraulic fluid
- Store pressurized fluid for emergency operations (Correct answer)
- Cool hydraulic fluid
- Increase pump displacement
Correct answer: Store pressurized fluid for emergency operations
A hydraulic accumulator stores pressurized fluid to provide emergency power for retracting the aerial if the primary pump fails.
Question 6: What does a high hydraulic fluid temperature typically indicate during aerial apparatus operation?
- Proper system function
- Excessive load cycles or restricted flow (Correct answer)
- Correct fluid viscosity
- New pump break-in period
Correct answer: Excessive load cycles or restricted flow
High hydraulic fluid temperature usually signals excessive load cycling, restricted flow, or a failing component causing heat buildup.
EVT EVT Hydraulic Systems & Aerial Apparatus 1
What is the primary function of a hydraulic relief valve in an aerial apparatus system?