Answer:
Auto recirculation valve is used to ensure a minimum flow is maintained through the pump all the time. Recirculation valves are mostly combined with Non Return Valves in the main flow pipe , when flow is established through the discharge line which means that the NRV is open , recirculation valve is closed through a mechanical linkage between the NRV and recirculation valve .
Usually the recirculation valves develops passing through it after a period of time due to wear out in the contact points between the NRV and recirculation linkages.