Two typical flow control problems are recirculation and warm-up. Because of the large pressure drops involved with high temperature liquids, the fluid may flash.  This erodes both the  valve and the downstream piping.  Additional problems include unacceptable noise and vibration of the piping.

Backpressure Regulators (BPRs)  offer a solution to these problems.  They are installed in the recirculation piping - normally at or near the return vessel.  When there is recirculation flow, the BPR opens, and compresses a calibrated spring.  This protects the complete bypass system against cavitation and flashing.