The Bendix+ R-7 modulating valve is used in conjunction with a dual air brake system and spring brake actuators. Typically the R-7 modulating valve performs four functions: 1. Limits hold-off pressure to the spring brake actuators. 2. Provides a quick release of air pressure from the spring cavity of the spring brake actuator allowing a fast application of the spring brake actuators. The valve delivers air to the park brake quick release valve (or relay) and also releases air in the control line to the quick release valve (or relay). 3. Modulates spring brake actuator application should a failure occur in the primary service brake system. 4. Prevents compounding of service and spring forces.