Hydraulics
1.5 hours
Learning Objectives
- •Describe the basic components of a loader crane hydraulic system
- •Explain how the PTO and pump supply hydraulic power on a truck-mounted crane
- •Identify common hydraulic faults: leaks, contamination, and overheating
- •State the safety hazards of hydraulic fluid under pressure
Topics Covered
- •Power take-off (PTO): draws power from the truck transmission to drive the hydraulic pump
- •Hydraulic pump, reservoir, filter, and fluid: the source side of the system
- •Control valves: direct flow to the boom, slew, extension, and stabilizer cylinders
- •Cylinders and hydraulic motors: convert fluid pressure into boom and slew motion
- •Hoses, fittings, and quick couplers: common leak and failure points
- •Relief valves and holding (counterbalance) valves: limit pressure and hold the load if a hose bursts
- •Common faults: external leaks, fluid contamination, aeration, and overheating
- •Hazards: high-pressure pinhole leaks can inject fluid into skin — never search for leaks by hand
- •Checking fluid level, condition, and temperature as part of the daily inspection
Resources
Self-Check Questions
Question 1: On a truck-mounted loader crane, what is the role of the power take-off (PTO)?
- A. It is a backup braking system for the truck
- B. It draws power from the truck transmission to drive the hydraulic pump(correct)
- C. It is the operator control joystick
- D. It locks the boom for transport
Show Explanation
Explanation:
The PTO taps mechanical power from the truck transmission and uses it to turn the hydraulic pump. If the PTO is not engaged correctly, the crane has no hydraulic power.
Question 2: You suspect a pressurized hydraulic hose has a small leak. How should you locate it?
- A. Run your bare hand along the hose to feel for spray
- B. Use a piece of cardboard or paper, keeping hands and body clear, with the system depressurized when possible(correct)
- C. Look directly at the suspected spot from a few inches away
- D. Wipe the hose with a rag while the system is at full pressure
Show Explanation
Explanation:
A high-pressure pinhole leak can inject hydraulic fluid through skin, causing severe injury. Never search by hand — use cardboard, keep clear, and depressurize the system where possible.
Question 3: What is the function of a holding (counterbalance) valve on a boom cylinder?
- A. It speeds up boom movement
- B. It holds the load in place and prevents the boom from dropping if a hose fails(correct)
- C. It heats the hydraulic fluid in cold weather
- D. It disengages the PTO automatically
Show Explanation
Explanation:
Holding or counterbalance valves keep the cylinder from collapsing if downstream pressure is lost, such as from a burst hose. They are a critical safety feature that prevents sudden uncontrolled load drops.
Question 4: During a daily check you find the hydraulic fluid is milky and foamy. This most likely indicates:
- A. The fluid is fresh and ready to use
- B. Air or water contamination in the system(correct)
- C. The crane has extra lifting capacity
- D. The PTO is over-engaged
Show Explanation
Explanation:
Milky or foamy fluid indicates aeration or water contamination. Contaminated fluid causes spongy, unpredictable control response and accelerates wear; the cause must be found and corrected.
Question 5: Why is hydraulic system overheating a concern on a loader crane?
- A. It improves lifting performance
- B. It degrades the fluid, reduces lubrication, and can cause seal failure and erratic operation(correct)
- C. It only matters in winter
- D. It has no operational effect
Show Explanation
Explanation:
Overheated fluid thins out, loses its lubricating and sealing properties, and breaks down chemically. This leads to seal failure, erratic control, and component damage, so rising temperature should not be ignored.
Question 6: Which of the following is part of a proper daily hydraulic check?
- A. Disassembling the pump to inspect internal gears
- B. Checking fluid level and condition and looking for leaks at hoses, fittings, and cylinders(correct)
- C. Refilling the reservoir with motor oil
- D. Adjusting the relief valve pressure setting
Show Explanation
Explanation:
The daily check is visual and external: verify fluid level and condition and scan hoses, fittings, and cylinders for leaks or damage. Internal repairs and valve adjustments are for qualified technicians, not the daily routine.