This Automatic Liquid Flow Regulator Type FRVA regulates the liquid flow automatically for ammonia overfeed systems. It is a well-built, durable piece of machinery that regulates liquid flow..This Automatic Liquid Flow Regulator Type FRVA regulates the flow of liquid to the evaporator and guarantees a steady flow when changed. As a check valve, it also prevents backflow from the evaporator into the liquid line during pressure reversals that happen during hot gas defrost. In many pressure settings, it automatically makes up for differences.