The Ratio Feature is considered a benefit in hard stop situations & refers to the relationship between the control air pressure to the valve & the delivered air pressure from the valve to the service brake chambers.
During normal stopping a 1:1 ratio exists between the control & delivered air pressures. In a hard stop the ratio momentarily changes to 1:1.5 until valve lap-off occurs and the 1:1 ratio is restored. This change takes place in less then 1/100th of a second.
The preferred application for valves with this feature is controlling tandem axles..
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