What Is an Air Hoist?
An air hoist is a hoisting machine that uses an air motor instead of an electric motor to drive the hoist. Unlike electric motors, air hoists do not require concern for ignition or power supply voltage, making them safe for use in areas with ignition risks, such as chemical plants. Powered by compressed air, air hoists are primarily used for transporting lightweight workpieces. They offer adjustable speeds through push buttons, levers, or pull cords and are lighter and smaller than explosion-proof electric hoists of the same capacity.
There are two main types of air hoists: chain-based and wire-based. Generally, the chain type is preferred for heavier workpieces than those suited for the wire type.
Uses of Air Hoists
Since air hoists do not rely on electricity for operation, they are ideal for explosive environments like chemical plants, tunnel construction sites, mine shafts, and steel mills. They excel in production lines needing light workpiece handling or speed. Simple to operate, air hoists only require connecting to a compressed air hose. Compared to electric motors, they are lightweight, compact, and relatively easy to install, making them suitable for temporary or provisional production lines.
For horizontal movement, manual or air motor-driven trolleys transport products, parts, and equipment like luggage and jigs.
Principle of Air Hoists
An air hoist comprises an air motor, brake, reduction gear, control valve, operating equipment, safety devices, and trolley equipment.
1. Air Motor
The air motor, either rotary vane or radial piston type, serves as the driving source. The rotary vane type features a rotor within an eccentrically shaped cylinder, housing several radially movable vanes. The radial piston type incorporates pistons within star-shaped cylinders. Lubrication-free motors, which do not emit oil in the exhaust, require minimal maintenance, operating at compressed air pressures of about 0.4 to 0.6 MPa.
2. Brake
Brakes are essential for holding the load. A combination of an engine brake, leveraging the air motor’s characteristics, and a cone brake, linked to a control valve, provides strong braking force.
3. Reduction Gear
Compact and lightweight planetary differential gears, known for their large reduction ratios, reduce the air motor’s high speed to the winder’s speed.
4. Control Valve
A direct-acting spool valve, operable via a lever or pull string, allows for step-less speed adjustment.
5. Safety Devices
Certain models feature reverse winding prevention and overload stop devices.
Types of Air Hoists
Air hoists come in chain and wire rope variations.
1. Chain Type
Featuring a durable and tough chain, this type uses surface-hardened alloy steel load chains that can be extended.
2. Wire Rope Type
The lightweight wire rope type includes a reverse winding prevention device, automatically stopping the air motor when the rope is fully extended.
How to Choose Air Hoists
Air hoists, being smaller and lighter than electric chain hoists of equivalent capacity, perform well under challenging conditions such as extreme temperatures, high humidity, and explosive atmospheres. They eliminate the risk of motor coil burnout, even after prolonged use or inching. Speed adjustments are made by pressing or releasing a pendant-type pushbutton, allowing control over the hoisting and lowering speeds to match the task. Their mechanical brake construction ensures high durability and reliable braking force.