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One of the earliest air suspensions was built in the 1800’s. It was made up of goat skin bags with flapper valves. The valve would let air into the bag when the vehicle bounced in one direction and trap air in the bag when the axle tried to move in the opposite direction. This action provided a supply of air to the bag when the vehicle bounced up and cushioned the impact of the bump when the vehicle came back down. That application was for rail train passenger cars. Even then, air was recognized as vastly improving ride quality for vehicles, passengers and cargo. Until the early 70’s air suspensions were generally only applied to special vehicles requiring extra care for cargo, special axle to axle load distribution and liftable axles for heavy dump trucks. At that time, approximately only 3% of all of the vehicles on the highway were equipped with air suspensions. The cost and maintenance requirements restricted the use of air suspensions for many years. During the 70’s and 80’s, technology and the understanding of air suspensions improved greatly. Suspensions that previously required maintenance every 30 days were improved to require visual inspection only and were designed to last many years and thousands of miles without requiring any hands on maintenance at all. From then until now, usage of air suspensions has increased on class 8 trucks and trailers to about 85% and 65% respectively. The use of air on passenger automobiles and on - off highway sports vehicles has also increased dramatically during this time period. Although the cost of an air suspension is still higher than steel or rubber suspensions, the value of the air suspension is recognized to provide an excellent return on investment. This value comes in the form of longer trailer life, decreased damage to equipment and cargo, and improved ride conditions provided for animals and the person towing the trailer. Bolts, rivets, welds, aluminum trailer skins, and lighting connections all benefit from the softer air ride. Air also provides a constant ride height along with a level floor no matter how the load is distributed. In most cases, an air suspended trailer will have an increased value over spring or rubber sprung trailers at trade in time. Suspension Technology Industries, “STI”, used the technology learned during the early development of air suspensions to design an air suspension specifically built for smaller trailers. These trailers normally carry cargo such as horses, automobiles, electronics, living quarters or any of the thousands of uses for bumper pull and goose neck trailers. Most air suspensions will consist of air springs (bags), an axle, a structure to hold the axle that allows up and down movement of the wheel and brackets to attach the suspension to the trailer frame.
STI’s approach to the suspension design was to keep everything as simple as possible. The axle was eliminated and replaced with a 3” x 4” crosstube that does not require additional crossmembers when mounting to the trailer frame. The crosstube is attached directly to the trailer frame and actually adds to the strength of the trailer. Nothing on the suspension projects up into the area above the bottom of the trailer frame. At each end of the crosstube there are rotating shafts with swing arms attached to one end. These swing arms hold the wheel spindle. They are not connected from side to side making the suspension an independent wheel suspension. The shaft is mounted in housings that are attached to the crosstube and rotates in composite bushings. The bushings are very low maintenance and only require greasing at the same time that the wheel ends are given their normal service maintenance. Unlike suspensions that have a separate axle, the swing arms on the STI unit may be removed one side at a time in the event a wheel spindle is damaged. A small but rugged trailing beam is attached to the swing arm shaft with “U” bolts. This beam supports and protects the air spring that provides cushion for the ride. The beam is designed to provide the same ground clearance with or without air in the air spring. The air spring is manufactured like a tire. Fibers are wound to shape and covered with a rubber coating. They are very rugged and normally last for years. Air springs also have a bumper mounted inside that acts as a stop when the system has no air. The trailer can actually be moved short distances when required on the bumpers without causing damage to the suspension.
Wheel end equipment for all capacities is available. The most popular units are the 7k, 8k, and 10k. A full selection of brakes is also available including the electric and hydraulic drum, the hydraulic disc and the STI Cargo-Max hydraulic disc. STI developed hydraulic disc brake wheel end equipment, Cargo-Max, for 10k Model LBS suspensions. The Cargo-Max allows maximum space usage of the inside of the trailer by mounting the disc brakes inside the profile of the tire. In some cases, this allows two 10k axles to be used in place of three 7k axles without compromising inside cargo space and actually gaining cargo space.
In many instances the vehicle towing the smaller trailers does not have an air supply. In this situation, an air supply system with a small compressor is required. The system is very simple and will provide excellent service if installed and maintained properly. A fully charged battery, proper size wire, tight electrical connections, good grounds and periodically draining the air reservoir insures trouble free service. START UP .. Connect trailer to the tow vehicle and raise landing gear ( Jacks ). Remove tire stop blocks.
The light side of the trailer may raise first. This is normal.
SHUT DOWN .. Visually check around the trailer for anything unusual and that the trailer is clear to lower.
GOOD RULES OF THUMB:
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