Early versions of air suspension systems were relatively simple. Air bags replaced the coil springs. The bag was inflated to the correct pressure or height with an outside compressor through a valve on the bag. Changes in technology and use added more components, and control, to the system. But today's air suspension systems all have a basic stock of similar components that vary little from maker to maker. The differences come mainly in controls and ease of installation.
Air bag material has changed little over time. The bag is a composite of rubber and polyurethane, which provides structural integrity, air-tight construction, toughness against light abrasion from road debris and sand, and resistance to salt and chemical corrosion.
The bags come in three basic shapes:
- Double-convoluted bag. This bag is shaped like an hourglass. The design allows for a little more lateral flexibility than the other designs.
- Tapered sleeve. This air bag performs the same as any other but is designed to fit in a tighter area and offers a little more adjustability on ride height.
- Rolling sleeve. This is also a specific-application air bag. The pertinent differences between the two sleeves are really about ride height and spring control, and what's best for the vehicle and the application.
Most air suspension systems now come with an on-board compressor. The compressor is an electric pump feeding air to the bags through a series of compressed air lines. The compressor is generally mounted on the vehicle's frame, or in the trunk. The vast majority of compressors come with an attached drier. The compressor works by drawing outside air into the pump, compressing it and moving it to the bags. Outside air is often laden with moisture, and moisture can wreak havoc in a closed system. The drier uses a substance known as a desiccant to absorb as much moisture from the air as possible before the air is sent through the system.
Simpler compressor systems rely on the compressor itself to maintain, increase or decrease pressure. More advanced systems add an air tank to maintain pressure and provide an even transition between pressures. Compressors can be activated manually or automatically, and controlled solely by the driver, automatically through an electronic system, or a combination of both.