Aerial ladder fire trucks are mainly subdivided into three types: elevated platform fire trucks, ladder fire trucks, and aerial spraying fire trucks. They are all designed for high-altitude rescue operations. Let's take a look at their basic structures first.
Chassis: The chassis is the foundational structure of the entire vehicle. Its primary function is to assemble all the components of the fire truck and provide support.
Power Take-Off (PTO): Also known as the power take-off device, commonly referred to as the PTO. The PTO consists of the power take-off unit, drive shaft, hydraulic pump, and water pump. Depending on the location of the PTO, it can be divided into four types, each installed in different positions based on its purpose:
Side-mounted PTO: Power is taken from the side of the transmission. It has a relatively small output power and is mostly used for short-distance transport.
Countershaft PTO: Power is taken from the second shaft behind the transmission. It is installed behind the transmission and in front of the power take-off unit.
Split-shaft PTO: Power is taken from the drive shaft behind the transmission. It includes a transfer case, which is installed between the drive shafts behind the transmission and mounted between the longitudinal beams of the frame. This PTO configuration is found in sprinkler trucks and some special airport fire trucks.
Sandwich PTO: Also known as a full-power or full-capacity power take-off, it is installed on the first shaft of the transmission, i.e., behind the flywheel housing and in front of the transmission. The output power can reach up to 90%. It is the mainstream configuration for heavy-duty pump trucks and aerial ladder fire trucks.
Frame and Outriggers: The auxiliary frame is an additional frame mounted on top of the main frame. It primarily carries the upper components and provides support during operations to ensure the balance of the entire vehicle. The auxiliary frame includes four outriggers. The outriggers are generally operated by horizontal and vertical hydraulic cylinders for extension and retraction. The cylinders are equipped with bidirectional hydraulic locks for protection. Each outrigger can be adjusted independently to adapt to different terrains. Outriggers are usually equipped with clearance lights for safe nighttime operations.
Luffing Mechanism: The luffing mechanism consists of luffing cylinders and balance valves. Its main function is to raise and lower the boom.
Telescoping Mechanism: The telescoping mechanism is generally composed of telescopic cylinders, balance valves, plate chains, sprockets, and steel wire ropes. Its main function is to achieve the extension and retraction of the lifting boom.
Slewing Mechanism: The slewing mechanism consists of a hydraulic motor, slewing reducer, and slewing gear. Its function is to transmit torque and enable the rotation of the turntable.
Turntable: The turntable assembly plays a pivotal role. The upper part of the turntable carries the boom, luffing mechanism, and control console, while the lower part is mounted on the auxiliary frame.
Electrical Control Unit System: The electrical control unit system is the most complex part but also the most important. The entire system consists of electronic controllers, safety systems, alarm and communication systems, and lighting systems. The entire system controls the electrical, hydraulic, and pneumatic systems to coordinate the operation of the entire vehicle.
Hydraulic System: The hydraulic system uses electro-hydraulic proportional control. It consists of a computer system, electro-hydraulic proportional valves, pressure valves, flow valves, oil tank, oil filter, hydraulic motor, cylinders, oil pipes, and pipeline joints. The operation of the entire vehicle can only be achieved under the control of the computer and electrical system.
Work Platform: The work platform is connected to the front end of the lifting boom, also known as the high-altitude rescue cage. The front of the platform has a movable door that can be opened for rescue operations when approaching the windows of high-rise buildings. The platform is also equipped with a fire monitor that can swing up, down, left, and right for spraying. It also has external supply interfaces for attaching hoses and carrying water guns for rescue operations. The platform is equipped with a sprinkler system.
Control Console: The control console varies depending on the purpose of the fire truck. However, in high-end aerial ladder trucks, it can basically integrate the control consoles of all fire trucks. It includes a lower vehicle control console, pump box control console, turntable control console, and work platform control console. The control console consists of N buttons, N switches, N indicator lights, gauges, display screens, and two control levers.
Leveling Mechanism: The function of the leveling mechanism is to ensure that the work platform remains in a horizontal state at all times. It is divided into two types: automatic leveling and mechanical leveling.
Automatic Leveling Mechanism: The automatic leveling mechanism consists of angle sensors, a control module, leveling cylinders, chains, and sprockets. The system control is an electro-hydraulic proportional closed-loop servo control system. The sensor is installed on the work platform. When a tilt is detected, the tilt signal is automatically transmitted to the control module, which issues a command to the cylinders to work, driving the chains and sprockets to rotate the platform for self-adjustment.
Mechanical Leveling Mechanism: The mechanical leveling mechanism uses a parallelogram lever for follow-up adjustment. It consists of levers, chains, sprockets, and auxiliary supports.
