Air springs contain a column of air in an elastomeric bellow or sleeve to provide suspension, isolation, or actuation. Commonly found in vehicle suspension systems, occasionally in conjunction with a coil spring, they are also used to insulate vibration in machinery and as linear or angular actuators.

Air springs are employed through the use of an air compressor which fills and empties the pliable air bladder. The load is not distributed to the rubber liner, which only serves to contain the gas; the weight is attached to a piston or bead plate, which is directly supported by the air with very little deflection. A self-leveling mechanism is common to keep the air spring's load stable, and occasionally a separate coil spring is incorporated into the design. Also available are electronic air spring systems that can monitor air pressure, filter compressor air (preventing damage to the rubber bellows), and a lock to keep air inside of the spring in case of compressor or air line failure.

Air springs are most common in vehicle suspensions, but can also be used to keep vibrating/rotating machinery from affecting other components. Occasionally used as actuators, air springs can provide linear and angular translation.

Air Spring Composition

 Convoluted air spring; Rolling lobe air spring

• Air fitting: A tapped hole allowing for the spring to be fed from the air compressor
• Nut/bolt/mount: The method for attaching the air spring to the component. Some air springs incorporate a bolt and air fitting combination device.
• Bead plate: Crimped metal plate enclosing the spring and allowing attachment. This is typically forged steel, cast zinc alloy or cast aluminum.
• Bellows: The physical, multi-layer material withholding the compressed gas. Usually made of neoprene or rubber.
• Girdle: Only found in air springs of convoluted design, separating the bellows chambers.

• Bumper: An optional layer of padding protecting the piston from damage if the air spring fails.

• Piston: The component attached to the machinery requiring suspension, which is in turn supported by the enclosed air. The piston housing is typically attached with further hardware.

Selecting Air Springs

Types of Air Springs

Outside of custom fabricated air springs, there are three available types of market-ready air springs.

1. Crimped, convoluted bellows, which attach the bellow to the bead plate by a permanent crimp in the plate. These provide good vibration isolation and linear/angular actuation, but are not for vehicle suspensions.
2. Sleeve bellows, which attach the bellows to the bead plate by an external clamp. This air spring type provides good vibration isolation, but only linear actuation. They are not typical in suspensions.
3. Rolling lobe bellows, which incorporate a piston at one end of the bellows, rather than a bead plate. This is most commonly found in vehicle suspensions, and is generally not recommended for vibration isolation. 

Crimped Bellow; Sleeve Bellow; Rolling Lobe Bellow

Air Spring Specifications

Installation

Though they have comparable capabilities, air springs are much cheaper than pneumatic cylinders and other springs. When deflated, air springs have a small footprint, making them easy to manipulate and connect to machinery.

Maintenance

Air springs tend to have low maintenance routines and some manufacturers state their air springs are maintenance-free (set and forget). Air springs do not require lubrication, nor do they have seals or guides that may become misaligned or damaged like with other springs. Indeed, the bellows of air springs are prone to dry rot, though this could take years to develop. Air springs should be stored in dry, dark areas at room temperature.

Environment

Due to its durability and simplicity, air springs are good for most industrial and commercial applications. Rubber and neoprene are susceptible to dry rot, so dehumidified conditions could shorten the service life of an air spring. Both rubber and neoprene are suitable for use in high/low temperature applications, but have considerably less heat tolerance than metal spring options. While usable up to 65°C, neoprene should not be used below -40°C, and rubber shouldn't be used in sites below -60°C.

Media

The name air spring is a bit of a misnomer, as the bellows of the spring can also accept other types of fluids such as nitrogen, carbon, water, and anti-freeze.

Applications

Air springs are widely utilized. Commonly as actuators in amusement park rides, packaging equipment, clutch systems, conveyor belts and scissor lifts, they also act as vibration insulators in centrifuges, commercial laundry machines, measuring and weighing machinery, and textile looms. While the air spring has impacted many industries like oil, logging, construction and manufacturing, it is most prominent in the automobile industry where the air spring is used in suspensions for vehicle brands like Lincoln, Cadillac, Hummer, and Jeep.  

Air springs outlined in gray

Standards

JASO C613 - Air springs for trucks and buses.

NAVISTAR TMS 1070 - Air springs, suspension component.

Resources

Enidine - Air Spring Technologies

eHow - How Air Bag Suspensions Work

Image Credits:

Firestone Industrial Products | Goodyear | Continental | Jeep