Some North American tractor manufacturers have suggested an official standard for air brakes on farm trailers and other towed equipment, similar to European air brake standards.
One of the benefits of air brakes is that air is completely replaceable. If air leaks, the compressor can easily produce more, says Brad Stage, an engineer with Mico, a world leader in building brakes for heavy equipment.
“One drawback with an air system is the need to have large tanks and other components to actuate the trailer brakes,” Stage said.
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“This significantly reduces the power-to-space ratio and increases trailer weight.”
If manufacturers do adopt air output as standard, a tractor’s hydraulic brakes would still be used by installing a hydraulic-to-air relay modulation valve, he added.
The valve works by sensing the incoming hydraulic pressure when an operator presses on the tractor’s brakes. This pressure is then converted to an air pressure outlet, which allows the air system mounted on the tractor to modulate air pressure from the tractor to the trailer. Air output pressure is in proportion to hydraulic input pressure. It can be set up so the trailer has slightly more braking pressure than the tractor.
“John Deere came to us about 10 years ago with this idea. Their big four-wheel-drive tractors pull a lot of heavy scrapers and land moving equipment. They have giant disc brakes on air systems for safety. So Mico designed these hydraulic over air relay valves.
“They handle up to 2,000 p.s.i. hydraulic pressure on the input side and 150 p.s.i. air pressure on the output side. To balance the brake bias between tractor and trailer, the hydraulic to air ratio can be adjusted anywhere from a low of 3:1 up to a high of 21:1.”
The valves are built as single, dual or tandem ports, and Mico will sell directly to farmers wanting to upgrade the brake systems on their own trailers. List price is US$1,079. The Mico part number for the single port valve is 03-469-002.
