Hydraulics & Controls
1.5 hours
Learning Objectives
- •Describe the major components of a MEWP hydraulic system and how they move the platform
- •Explain the function of upper (platform) and lower (ground) controls and the override relationship between them
- •Identify common control-system safety devices: interlocks, tilt alarms, and emergency stops
- •Describe how to lower a platform safely using the emergency descent / auxiliary power system
Topics Covered
- •Hydraulic system components: reservoir, pump, control valves, hoses, and lift/drive cylinders
- •How hydraulic pressure is converted into platform lift, boom motion, and drive/steer functions
- •Upper controls: the primary controls located in the platform
- •Lower controls: ground controls that can override the upper controls, used mainly for rescue and emergency lowering
- •Foot switch / enable device that must be held for the platform controls to function
- •Interlocks: drive-speed cutback when elevated, pothole-protection bars, and tilt sensors
- •Tilt alarm and overload sensing systems that warn or cut out functions when limits are exceeded
- •Emergency stop buttons at both the upper and lower control stations
- •Emergency descent / auxiliary power: the manual or backup means of lowering a stuck platform
- •Pre-use control function test: testing all functions through their full range before raising the platform
Resources
Self-Check Questions
Question 1: In a MEWP hydraulic system, what component converts hydraulic pressure into the linear force that raises the platform?
- A. The reservoir
- B. The control valve
- C. The lift cylinder(correct)
- D. The pump
Show Explanation
Explanation:
The pump generates flow and the valves direct it, but the lift cylinder is what converts that pressurized fluid into the straight-line pushing force that raises the platform.
Question 2: On a MEWP, what is the relationship between the upper (platform) controls and the lower (ground) controls?
- A. The upper controls always override the lower controls
- B. The lower controls can override the upper controls and are used mainly for rescue and emergency lowering(correct)
- C. The two control stations operate completely independently
- D. Only one control station can be powered at a time, selected with a key
Show Explanation
Explanation:
Ground controls can override the platform controls. This lets someone on the ground lower an incapacitated operator or recover a stuck platform — which is why the ground station must always be kept accessible.
Question 3: What is the purpose of the foot switch (enable device) found on many boom lift platforms?
- A. It sounds the travel alarm
- B. It must be held down for the platform function controls to operate, acting as a dead-man device(correct)
- C. It charges the battery
- D. It locks the turntable rotation
Show Explanation
Explanation:
The foot switch is a dead-man enable device. If the operator releases it, the function controls stop responding — a safeguard against accidental or unintended movement.
Question 4: A MEWP tilt alarm activates while the platform is elevated. What should the operator do?
- A. Continue working but move more slowly
- B. Stop, and lower the platform to bring the machine back within its level limits before doing anything else(correct)
- C. Extend the boom to counterbalance the tilt
- D. Ignore it if the platform feels stable
Show Explanation
Explanation:
A tilt alarm warns that the chassis is out of level beyond the safe limit. The correct response is to stop and carefully lower the platform — never try to "drive out" of a tilt condition with the platform up.
Question 5: What is the emergency descent (auxiliary power) system on a MEWP used for?
- A. Increasing platform drive speed
- B. Lowering the platform when the primary power or hydraulic system fails(correct)
- C. Boosting the platform above its rated height
- D. Charging the battery from the engine
Show Explanation
Explanation:
If the main power or hydraulics fail with the platform up, the emergency descent / auxiliary power system provides a backup means to lower it. Every operator should know where it is and how to use it before going up.
Question 6: When should the operator perform a full control-function test of a MEWP?
- A. Once a month
- B. Only after a repair
- C. Before each use, testing every function through its range while the platform is still low(correct)
- D. Only if the previous operator reported a problem
Show Explanation
Explanation:
A control-function test is part of the pre-use check every shift. Run every function through its full range near the ground so a fault shows up before the operator is elevated and exposed.