Automotive Trucks information on net.

The air suspension systems on which many modern heavy trucks ride is an interesting example of advanced automotive engineering. In many applications, older style leaf springs have been replaced by air bags, which control ride height and compensate for heavy loads. Constant pressure in the bags is maintained by an engine driven air compressor, which replenishes the air supply within the air bags.

At the heart of such systems is air leveling valve, typically actuated by a mechanical linkage. This valve admits more air when the distance between the axle and the frame decreases to less than a permitted minimum dimension. The same valve then exhausts air when the distance between the frame and axle becomes excessive.

In the past, this leveling valve has generally been viewed as the weak link in the air suspension system. The constant fill and exhaust operations is hard on valves and over time, they can wear to the point where there can be significant air leakage. If an excess of leakage occurs, the compressor will operate more frequently and fuel consumption will increase. And should the valve fail, the operation of the entire air suspension system can be compromised.

To address these durability concerns, Barksdale Controls, Los Angeles, Calif., has developed a compact, lightweight air valve designed to withstand the rigors of heavy truck operations. Featuring a rotary design, the Barksdale valves contain only one moving part and relies on lapped surfaces to effect a positive seal. The design is such that the compressed air does not flow across the sealing surfaces, but rather it moves directly through the inside diameter of the seal. Thus, normal contaminants that may exist in the airflow will not cause seal leakage, the company said.

Qualification testing has indicated that the valve is capable of well over 100 million cycles. According to Barksdale, one major Class 8 truck manufacturer that has installed the valve on 19 tractors operating in Canada has reported zero valve failures after 500,000 miles in over-the-road operation.

Valve operation is effected by the relative movement of two circular overlapping ports moving relative to each other. A ramped flow rate develops as the valve opens and closes, with no undesirable full-on/full-off behavior, the company said.

A 3 [degrees] deadband prevents nuisance actuation of the valve during normal suspension travel. Exhaust and fill times are 1.5 to 2.5 times quicker than other systems, the company said.

# posted by Medical Information : 5:03 AM