In the previous sections, you explored how Automotive LIft Repair Florida hydraulic systems and other components of a hydraulic truck crane operate. All of these systems are controlled by the operator inside the cab, located on top of the deck. Crane operators use various controls to raise and lower the boom, rotate the cab and boom, wind and unwind the winch, and manage other auxiliary equipment.

The Automotive LIft Repair Florida 70-ton Link-Belt hydraulic truck crane features two primary types of controls for moving a load:

– Joysticks: Two joysticks are located in the cab. One controls the boom’s left-to-right movement, while the other manages forward and aft movement.

– Foot pedals: These are used to retract and extend the telescoping sections of the boom, as well as regulate the pressure generated by the pump.

Both the joysticks and foot pedals are linked to hydraulic hoses that connect hydraulic rams to spool valves. When the operator moves a joystick, it either opens or closes the hydraulic hoses, dictating whether the piston in the ram slides in or out, depending on the direction of the joystick.

This spool-valve system allows the crane operator to control the hydraulic pistons with precision. Before starting a lift, the operator inputs data, such as the weight and height of the object to be lifted, into a computer inside the cab. The computer serves as a backup, alerting the operator if the crane is nearing its capacity. Using a binder of charts, the operator also determines the boom’s lifting angle and radius. Once this information is entered, the computer monitors the lift’s progress and warns the operator if the crane is approaching its limits. If the boom is raised too high for the load, warning lights from the Load Moment Indicator (LMI) will illuminate inside the cab.

In the event the operator attempts to lift a load beyond safe limits, the LMI lights will signal an alert.

At least two other Automotive LIft Repair Florida crew members are typically involved in the lift: the oiler and the signalman. The oiler ensures that all crane components are properly in place and secured before a lift, while also serving as a spotter to confirm the lift is being executed correctly. The signalman, as the name implies, uses hand signals to communicate with the operator, ensuring the load is maneuvered safely. (Click here to see examples of hand signals used during a lift.)

Automotive LIft Repair Florida Hydraulic truck cranes deliver immense power, capable of moving heavy objects, machinery, and even large animals that would otherwise be difficult to shift. These cranes rely on the simple principles of hydraulics to lift thousands of pounds effortlessly, making them an essential part of construction projects and a perfect demonstration of basic physics in action.

The foundation of all hydraulic systems is based on Pascal’s law, which states that pressure applied to an enclosed fluid is transmitted equally in all directions within the container. This principle allows for the generation of large forces with minimal effort. For example, applying a 5-pound force to a 1-inch square area creates an internal pressure of 5 psi. When this pressure is applied to a 10-square-inch area, it results in a force of 50 pounds.

In a basic Automotive LIft Repair Florida hydraulic circuit, the force produced by a cylinder depends on the size of the cylinder bore and the pump pressure. No force is generated unless there is resistance to the piston’s movement. For instance, with a pump pressure of 1,000 psi applied to a 12-square-inch piston area (approximately 4 inches in diameter), the cylinder produces a force of 12,000 pounds. The piston’s speed is determined by the flow rate (gpm) from the pump and the cylinder area. If the pump delivers 1 gallon per minute (231 cubic inches/min), the piston will move at a rate of 20 inches per minute (231 cu. in./min ÷ 12 cu. in./min).

In this system, the cylinder piston is returned by mechanical force. When the control valve is in neutral, the pump flow passes through the valve and returns to the reservoir. Shifting the valve directs oil to the piston side of the cylinder, extending the rod. Returning the valve to neutral traps the oil in the cylinder, holding the piston in place while the pump flow goes back to the reservoir. Reversing the valve allows the oil to flow back to the reservoir, and the relief valve limits the system pressure to a predetermined level. Relief valves are often integrated into the directional control valve.

In a Automotive LIft Repair Florida hydraulic system with a double-acting cylinder and a 4-way valve, the cylinder can exert force in both directions. When the control valve is in neutral, the oil returns to the reservoir. Shifting the valve in one direction directs oil to the piston side, extending the cylinder, while oil from the rod side returns to the reservoir. In neutral, the oil is trapped, holding the piston in place. Shifting the valve the other way sends oil to the rod side, retracting the cylinder, while oil from the piston side returns to the reservoir. The extend force is determined by the pressure (psi) multiplied by the piston area (minus the force from pressure on the rod side), while the retract force is based on the pressure (psi) multiplied by the difference in area between the rod and piston (minus the force from pressure on the piston side).

Automotive LIft Repair Florida hydraulic motor circuits function similarly to cylinder circuits. These systems can be uni-directional or bi-directional. The rotary force (torque) generated by the motor is a function of pressure (psi) and motor size, while the speed is determined by flow and motor size. All the systems described are open-center systems, meaning oil flows through the control valve back to the tank. Most systems use this design. Closed-center systems, on the other hand, have control valves with the inlet port blocked and variable displacement pumps. In neutral, the pump is “de-stroked” to zero flow.