The Low Pressure Constant Volume Regulator limits airflow to a set maximum volume (CFM). Its effective pressure range is between 0.1 and 0.4 InWC. The CVR “wing” starts to fly and therefore comes online a little earlier. It provides a little bit of resolution at the low end of the spectrum.
Low Pressure CVRs are available in 3″, 4″ and 5″ sizes with airflow ranges between 6 and 70 CFM.