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 & the 1:1 ratio is restored. This change takes place in less than 1/100 of a second.
Do not use ratio feature valves on converter dollies, trailer turntable axles or lift axles.
