10-09-2013, 04:39 PM
INTRODUCTION TO AIR SUSPENSIONS
AIR SUSPENSIONS[.pdf (Size: 209.11 KB / Downloads: 118)
BASIC AIR SUSPENSION
2-1 What is an air suspension? An air suspension supports the vehicle on the axles with an arrangement
of air bags instead of some type of steel spring, leaf or coil, or some type of torsion spring arrangement.
The air bags are sometimes referred to as air springs or bellows. Suspensions that have steel or torsion
springs that are supplemented by the use of air bags are not considered air suspensions. There are
combination systems that have both air and steel springs. Usually the air suspension components are used
on the rear of the vehicle. Depending on the situation, this type of air suspension will probably have to be
dealt with for leveling purposes.
Normally, the air suspension is just one part of the air system on the vehicle. Most (but not all) vehicles
with an air suspension also have air brakes along with other equipment that may be operated with air. Any
of these other systems can cause problems with the air suspension. Other air systems including the brake
systems in general, will not be discussed in this school. It is important to understand that on vehicles with
air systems, especially with air brakes, manufacturers must follow specific regulations when designing
their air systems. The brake system will always be the main concern for the air system. There will be
safety features installed in the system that make the brake system the main priority for the air system.
AGAIN, I CANNOT STRESS ENOUGH THE IMPORTANCE OF CONTACTING THE VEHICLE,
CHASSIS OR SUSPENSION MANUFACTURER BEFORE ATTEMPTING TO DEAL WITH A
SUSPENSION OR BRAKE ISSUE.
Air bags.
Air bags are simply a rubber bladder that holds air. Air bags are also referred to as air
springs or bellows. The air bags are located between the frame of the vehicle and the vehicle axles. Air
bags are rated for weight and pressure capacities.
Air bag placement and arrangements vary amongst chassis manufacturers. At the very least, there will be
one air bag for each side of each axle in the vehicle. There can be two air bags for each side of the axles
but I have never seen a tag axle with more that one bag per side. Some manufacturers use two air bags for
each side of the drive axle and some use two air bags for each side of the drive and front axles. Space
between air bags for side to side placement also varies. Some place the air bags outboard as far as they can
and some have the bags closer together. When two bags per side are used, one will be in front of the axle
and the other behind the axle. Again, spacing can vary.
HOW THE AIR SUSPENSION FUNCTIONS
Before explaining how the air suspension functions, there are two important things you need to
understand. The first thing is the term “ride height”. Ride height is simply the distance between the frame
of the vehicle and the vehicle axles that the vehicle rides at. Ride height is determined by the vehicle or
chassis manufacturer. Ride height varies between vehicles and manufacturers. Ride height information
must be obtained from the vehicle or chassis manufacturer. The manufacturer will supply the correct
measurements and measuring points on the chassis. An example would be; Ride height should be
seventeen inches measured between the center of the top shock mounting bolt to the center of the bottom
shock mounting bolt. Remember, this is only an example of what the ride height information may be. The
second thing you must understand is that air is highly compressible. What this means is the frame of the
vehicle will move up or down (without adding air to or exhausting air from the air bags) when weight is
removed or added to the vehicle. Although this is true of any suspension, air, spring or torsion, vehicles
with a spring or torsion suspension will remain raised or lowered when weight is removed or added.
Because of the height control valves, vehicles with air suspensions should always remain at the proper ride
height. The ride height for other suspensions will change when weight is added or removed. Also, vehicles
with an air suspension will not “settle” with age as a spring or torsion suspension will.